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  • New Release of Oracle Berkeley DB

    - by Eric Jensen
    We are pleased to announce that a new release of Oracle Berkeley DB, version 11.2.5.2.28, is available today. Our latest release includes yet more value added features for SQLite users, as well as several performance enhancements and new customer-requested features to the key-value pair API.  We continue to provide technology leadership, features and performance for SQLite applications.  This release introduces additional features that are not available in native SQLite, and adds functionality allowing customers to create richer, more scalable, more concurrent applications using the Berkeley DB SQL API. This release is compelling to Oracle’s customers and partners because it: delivers a complete, embeddable SQL92 database as a library under 1MB size drop-in API compatible with SQLite version 3 no-oversight, zero-touch database administration industrial quality, battle tested Berkeley DB B-TREE for concurrent transactional data storage New Features Include: MVCC support for even higher concurrency direct SQL support for HA/replication transactionally protected Sequence number generation functions lower memory requirements, shared memory regions and faster/smaller memory on startup easier B-TREE page size configuration with new ''db_tuner" utility New Key-Value API Features Include: HEAP access method for constrained disk-space applications (key-value API) faster QUEUE access method operations for highly concurrent applications -- up 2-3X faster! (key-value API) new X/open compliant XA resource manager, easily integrated with Oracle Tuxedo (key-value API) additional HA/replication management and communication options (key-value API) and a lot more! BDB is hands-down the best edge, mobile, and embedded database available to developers. Downloads available today on the Berkeley DB download pageProduct Documentation

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  • How can I better implement A star algorithm with a very large set of nodes?

    - by Stephen
    I'm making a game with nodejs in which many enemies must converge on the player as the player moves around a relatively open space (right now it is an open field with few obstacles, but eventually there may be some small buildings in the field with 1 or 2 rooms). It's a multiplayer game using websockets, so the server needs to keep track of enemies and players. I found this javascript A* library which I've modified to be used on the server as a nodejs module. The library utilizes a Binary Heap to track the nodes for the algorithm, so it should be pretty fast (and indeed, with a small grid, say 100x100 it is lightning fast). The problem is that my game is not really tile-based. As the player moves around the map, he is moving on a more or less 1-to-1 per-pixel coordinate system (the player can move in 8 directions, 1 or 2 pixels at a time). In preliminary tests, on an 800x600 field, the path-finding can take anywhere from 400 to 1000 ms. Multiply that by 10 enemies and the game starts to get pretty choppy. I have already set it up so that each enemy will only do a path-finding call once per second or even as slow as once every 2 seconds (they have to keep updating their path because the players can move freely). But even with this long interval, there are noticeable lag spikes or chops every couple of seconds as the enemies update their paths. I'm willing to approach the problem of path-finding differently, if there's another option. I'm assuming that the real problem is the enormous grid (800x600). It also occurs to me that maybe the large arrays are to blame, as I've read that V8 has trouble with large arrays.

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  • Did the developers of Java conciously abandon RAII?

    - by JoelFan
    As a long-time C# programmer, I have recently come to learn more about the advantages of Resource Acquisition Is Initialization (RAII). In particular, I have discovered that the C# idiom: using (my dbConn = new DbConnection(connStr) { // do stuff with dbConn } has the C++ equivalent: { DbConnection dbConn(connStr); // do stuff with dbConn } meaning that remembering to enclose the use of resources like DbConnection in a using block is unnecessary in C++ ! This seems to a major advantage of C++. This is even more convincing when you consider a class that has an instance member of type DbConnection, for example class Foo { DbConnection dbConn; // ... } In C# I would need to have Foo implement IDisposable as such: class Foo : IDisposable { DbConnection dbConn; public void Dispose() { dbConn.Dispose(); } } and what's worse, every user of Foo would need to remember to enclose Foo in a using block, like: using (var foo = new Foo()) { // do stuff with "foo" } Now looking at C# and its Java roots I am wondering... did the developers of Java fully appreciate what they were giving up when they abandoned the stack in favor of the heap, thus abandoning RAII? (Similarly, did Stroustrup fully appreciate the significance of RAII?)

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  • Firefox on wine crashes on startup on Ubuntu

    - by Iam Zesh
    First, let's explain why I want Firefox under wine, and not the Firefox that is shipped out of the box with Ubuntu. I want to use Firefox under wine because I want to use the Widevine addon, which is "at this time not available for linux". Here is what I did so far to install and use Firefox on wine. On Ubuntu 12.04 LTS, I just installed wine like that: sudo apt-get update; sudo apt-get install wine Then I downloaded the windows installer for Firefox from the mozilla website. I ran the Firefox Setup 25.0.exe file with wine but at the end of the install process when launching Firefox, I got a window notifying me that the program at crashed. I ran Firefox from the command line with wine, to get an idea of what could have went wrong: wine /home/myUser/.wine/drive_c/Program\ Files/Mozilla\ Firefox/firefox.exe fixme:heap:HeapSetInformation (nil) 1 (nil) 0 fixme:process:SetProcessDEPPolicy (1): stub fixme:iphlpapi:NotifyAddrChange (Handle 0x368e8fc, overlapped 0x368e8e0): stub fixme:winsock:WSCGetProviderPath ({e70f1aa0-ab8b-11cf-8ca3-00805f48a192} 0x44fe6f8 0x44fe6b8 0x44fe6e4) Stub! fixme:advapi:RegisterTraceGuidsW (0x1b0e290, 0x39ead80, {509962e0-406b-46f4-99ba-5a009f8d2225}, 3, 0x3974d00, (null), (null), 0x39eadb0,): stub fixme:winsock:WSCGetProviderPath ({e70f1aa0-ab8b-11cf-8ca3-00805f48a192} 0x44fe6f8 0x44fe6b8 0x44fe6e4) Stub! fixme:winsock:WSCGetProviderPath ({11058240-be47-11cf-95c8-00805f48a192} 0x44fe6f8 0x44fe6b8 0x44fe6e4) Stub! fixme:winsock:WSCGetProviderPath ({11058241-be47-11cf-95c8-00805f48a192} 0x44fe6f8 0x44fe6b8 0x44fe6e4) Stub! fixme:winsock:WSCGetProviderPath ({11058241-be47-11cf-95c8-00805f48a192} 0x44fe6f8 0x44fe6b8 0x44fe6e4) Stub! fixme:ntdll:NtLockFile I/O completion on lock not implemented yet fixme:advapi:SetNamedSecurityInfoW L"C:\\users\\myUser\\Application Data\\Mozilla\\Firefox\\Profiles\\cn4oy6kh.default\\extensions.ini" 1 536870916 (nil) (nil) 0x13d40c (nil) fixme:imm:ImmReleaseContext (0x20022, 0x13e850): stub fixme:win:EnumDisplayDevicesW ((null),0,0x32ee18,0x00000000), stub! fixme:shell:ApplicationAssociationRegistration_QueryCurrentDefault (0x143b50)->(L"webcal", 1, 1, 0x32c7a0) fixme:shell:ApplicationAssociationRegistration_QueryCurrentDefault (0x143b50)->(L"ircs", 1, 1, 0x32c7a0) fixme:shell:ApplicationAssociationRegistration_QueryCurrentDefault (0x143b50)->(L"mailto", 1, 1, 0x32c7a0) fixme:shell:ApplicationAssociationRegistration_QueryCurrentDefault (0x143b50)->(L"irc", 1, 1, 0x32c7a0) fixme:alsa:AudioSessionControl_SetGroupingParam (0x153050)->({7b0a93ee-05e7-4576-9cc5-64fdf201f303}, (null)) - stub fixme:alsa:AudioSessionControl_SetGroupingParam (0x153050)->({00000000-0000-0000-0000-000000000000}, (null)) - stub fixme:alsa:AudioSessionControl_UnregisterAudioSessionNotification (0x153050)->(0x6311880) - stub wine: Call from 0x7b839cf2 to unimplemented function dwmapi.dll.DwmGetCompositionTimingInfo, aborting fixme:dbghelp:elf_search_auxv can't find symbol in module Unfortunately I don't know what to do from there on...

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  • Why is Quicksort called "Quicksort"?

    - by Darrel Hoffman
    The point of this question is not to debate the merits of this over any other sorting algorithm - certainly there are many other questions that do this. This question is about the name. Why is Quicksort called "Quicksort"? Sure, it's "quick", most of the time, but not always. The possibility of degenerating to O(N^2) is well known. There are various modifications to Quicksort that mitigate this problem, but the ones which bring the worst case down to a guaranteed O(n log n) aren't generally called Quicksort anymore. (e.g. Introsort). I just wonder why of all the well-known sorting algorithms, this is the only one deserving of the name "quick", which describes not how the algorithm works, but how fast it (usually) is. Mergesort is called that because it merges the data. Heapsort is called that because it uses a heap. Introsort gets its name from "Introspective", since it monitors its own performance to decide when to switch from Quicksort to Heapsort. Similarly for all the slower ones - Bubblesort, Insertion sort, Selection sort, etc. They're all named for how they work. The only other exception I can think of is "Bogosort", which is really just a joke that nobody ever actually uses in practice. Why isn't Quicksort called something more descriptive, like "Partition sort" or "Pivot sort", which describe what it actually does? It's not even a case of "got here first". Mergesort was developed 15 years before Quicksort. (1945 and 1960 respectively according to Wikipedia) I guess this is really more of a history question than a programming one. I'm just curious how it got the name - was it just good marketing?

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  • Is NAN suitable for communicating that an invalid parameter was involved in a calculation?

    - by Arman
    I am currently working on a numerical processing system that will be deployed in a performance-critical environment. It takes inputs in the form of numerical arrays (these use the eigen library, but for the purpose of this question that's perhaps immaterial), and performs some range of numerical computations (matrix products, concatenations, etc.) to produce outputs. All arrays are allocated statically and their sizes are known at compile time. However, some of the inputs may be invalid. In these exceptional cases, we still want the code to be computed and we still want outputs not "polluted" by invalid values to be used. To give an example, let's take the following trivial example (this is pseudo-code): Matrix a = {1, 2, NAN, 4}; // this is the "input" matrix Scalar b = 2; Matrix output = b * a; // this results in {2, 4, NAN, 8} The idea here is that 2, 4 and 8 are usable values, but the NAN should signal to the receipient of the data that that entry was involved in an operation that involved an invalid value, and should be discarded (this will be detected via a std::isfinite(value) check before the value is used). Is this a sound way of communicating and propagating unusable values, given that performance is critical and heap allocation is not an option (and neither are other resource-consuming constructs such as boost::optional or pointers)? Are there better ways of doing this? At this point I'm quite happy with the current setup but I was hoping to get some fresh ideas or productive criticism of the current implementation.

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  • [Kubuntu 14.04][Eclipse] (ADT) crashes at button OK from Project properties

    - by nouseforname
    Since i upgraded to kubuntu 14.04, my Eclipse crashes at different situations. Mostly i can "simulate" it when going to project properties and press ok. Then it always crashes. My system: DISTRIB_ID=Ubuntu DISTRIB_RELEASE=14.04 DISTRIB_CODENAME=trusty DISTRIB_DESCRIPTION="Ubuntu 14.04.1 LTS" My Java: java version "1.8.0_05" Java(TM) SE Runtime Environment (build 1.8.0_05-b13) Java HotSpot(TM) 64-Bit Server VM (build 25.5-b02, mixed mode) My ADT Version: Android Development Toolkit Version: 23.0.0.1245622 I already tried to add this in adt-bundle-linux-x86_64/eclipse/configuration/configuration.ini org.eclipse.swt.browser.DefaultType=mozilla -Dorg.eclipse.swt.browser.DefaultType=mozilla Error: # # A fatal error has been detected by the Java Runtime Environment: # # SIGSEGV (0xb) at pc=0x00007fe049eb1718, pid=5964, tid=140601811232512 # # JRE version: Java(TM) SE Runtime Environment (8.0_05-b13) (build 1.8.0_05-b13) # Java VM: Java HotSpot(TM) 64-Bit Server VM (25.5-b02 mixed mode linux-amd64 compressed oops) # Problematic frame: # C [libgobject-2.0.so.0+0x19718] g_object_get_qdata+0x18 # # Core dump written. Default location: /home/maddin/core or core.5964 # # An error report file with more information is saved as: # /home/maddin/hs_err_pid5964.log Compiled method (nm) 28866 4166 n 0 org.eclipse.swt.internal.gtk.OS::_g_object_get_qdata (native) total in heap [0x00007fe051da6790,0x00007fe051da6af0] = 864 relocation [0x00007fe051da68b0,0x00007fe051da68f8] = 72 main code [0x00007fe051da6900,0x00007fe051da6ae8] = 488 oops [0x00007fe051da6ae8,0x00007fe051da6af0] = 8 # # If you would like to submit a bug report, please visit: # http://bugreport.sun.com/bugreport/crash.jsp # The crash happened outside the Java Virtual Machine in native code. # See problematic frame for where to report the bug. # Now, as soon as i change SystemSettings - Application Apperance - GTK - GTKn-Design to something else but "oxygen-gtk" this crash doesn't happen anymore. But the application appearance also is ugly. Beside that i get a lot of errors/warnings like that: (SWT:6148): GLib-GObject-CRITICAL **: g_closure_add_invalidate_notifier: assertion 'closure->n_inotifiers < CLOSURE_MAX_N_INOTIFIERS' failed or other GTK warnings from the particular design, not having theme-engine. Which actually doesn't cause any crahs it seems so far. So i have 3 options: accept crashes accept warnings (maybe the best choice) accept ugly design What can i do to solve this issue without changing the design settings?

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  • Space-efficient data structures for broad-phase collision detection

    - by Marian Ivanov
    As far as I know, these are three types of data structures that can be used for collision detection broadphase: Unsorted arrays: Check every object againist every object - O(n^2) time; O(log n) space. It's so slow, it's useless if n isn't really small. for (i=1;i<objects;i++){ for(j=0;j<i;j++) narrowPhase(i,j); }; Sorted arrays: Sort the objects, so that you get O(n^(2-1/k)) for k dimensions O(n^1.5) for 2d and O(n^1.67) for 3d and O(n) space. Assuming the space is 2D and sortedArray is sorted so that if the object begins in sortedArray[i] and another object ends at sortedArray[i-1]; they don't collide Heaps of stacks: Divide the objects between a heap of stacks, so that you only have to check the bucket, its children and its parents - O(n log n) time, but O(n^2) space. This is probably the most frequently used approach. Is there a way of having O(n log n) time with less space? When is it more efficient to use sorted arrays over heaps and vice versa?

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  • Did something just get borked with glibc/perl/irssi?

    - by Wayne Werner
    I was using irssi about 30 minutes ago now on Ubuntu server 12.04. Everything was perfectly fine and then all of the sudden something happened (my guess is a power failure). The box was restarted. When I logged back in and ran irssi, I got the following: *** glibc detected *** irssi: double free or corruption (out): 0x0000000002085a40 *** ======= Backtrace: ========= /lib/x86_64-linux-gnu/libc.so.6(+0x7e626)[0x7ffc01d87626] irssi(config_node_set_str+0x98)[0x491768] irssi[0x491f12] irssi[0x491e61] irssi(config_parse+0x52)[0x492112] irssi[0x48ab81] irssi(settings_init+0xd1)[0x48bf81] irssi(core_init+0x79)[0x47a849] irssi(main+0xd8)[0x4167e8] /lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xed)[0x7ffc01d2a76d] irssi[0x416b41] ======= Memory map: ======== 00400000-004d0000 r-xp 00000000 08:01 1319015 /usr/bin/irssi 006cf000-006d0000 r--p 000cf000 08:01 1319015 /usr/bin/irssi 006d0000-006dc000 rw-p 000d0000 08:01 1319015 /usr/bin/irssi 006dc000-006dd000 rw-p 00000000 00:00 0 02078000-02099000 rw-p 00000000 00:00 0 [heap] 7ffc0025b000-7ffc00270000 r-xp 00000000 08:01 655404 /lib/x86_64-linux-gnu/libgcc_s.so.1 7ffc00270000-7ffc0046f000 ---p 00015000 08:01 655404 /lib/x86_64-linux-gnu/libgcc_s.so.1 7ffc0046f000-7ffc00470000 r--p 00014000 08:01 655404 /lib/x86_64-linux-gnu/libgcc_s.so.1 7ffc00470000-7ffc00471000 rw-p 00015000 08:01 655404 /lib/x86_64-linux-gnu/libgcc_s.so.1 7ffc00471000-7ffc0073a000 r--p 00000000 08:01 1320172 /usr/lib/locale/locale-archive 7ffc0073a000-7ffc00746000 r-xp 00000000 08:01 655391 /lib/x86_64-linux-gnu/libnss_files-2.15.so 7ffc00746000-7ffc00945000 ---p 0000c000 08:01 655391 /lib/x86_64-linux-gnu/libnss_files-2.15.so 7ffc00945000-7ffc00946000 r--p 0000b000 08:01 655391 /lib/x86_64-linux-gnu/libnss_files-2.15.so 7ffc00946000-7ffc00947000 rw-p 0000c000 08:01 655391 /lib/x86_64-linux-gnu/libnss_files-2.15.so 7ffc00947000-7ffc00951000 r-xp 00000000 08:01 655392 /lib/x86_64-linux-gnu/libnss_nis-2.15.so 7ffc00951000-7ffc00b51000 ---p 0000a000 08:01 655392 /lib/x86_64-linux-gnu/libnss_nis-2.15.so Followed by many more lines. Is there anything I can do to fix this?

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  • Vector with Constant-Time Remove - still a Vector?

    - by Darrel Hoffman
    One of the drawbacks of most common implementations of the Vector class (or ArrayList, etc. Basically any array-backed expandable list class) is that their remove() operation generally operates in linear time - if you remove an element, you must shift all elements after it one space back to keep the data contiguous. But what if you're using a Vector just to be a list-of-things, where the order of the things is irrelevant? In this case removal can be accomplished in a few simple steps: Swap element to be removed with the last element in the array Reduce size field by 1. (No need to re-allocate the array, as the deleted item is now beyond the size field and thus not "in" the list any more. The next add() will just overwrite it.) (optional) Delete last element to free up its memory. (Not needed in garbage-collected languages.) This is clearly now a constant-time operation, since only performs a single swap regardless of size. The downside is of course that it changes the order of the data, but if you don't care about the order, that's not a problem. Could this still be called a Vector? Or is it something different? It has some things in common with "Set" classes in that the order is irrelevant, but unlike a Set it can store duplicate values. (Also most Set classes I know of are backed by a tree or hash map rather than an array.) It also bears some similarity to Heap classes, although without the log(N) percolate steps since we don't care about the order.

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  • CheckMemoryAllocationGame Sample

    - by Michael B. McLaughlin
    Many times I’ve found myself wondering how much GC memory some operation allocates. This is primarily in the context of XNA games due to the desire to avoid generating garbage and thus triggering a GC collection. Many times I’ve written simple programs to check allocations. I did it again recently. It occurred to me that many XNA developers find themselves asking this question from time to time. So I cleaned up my sample and published it on my website. Feel free to download it and put it to use. It’s rather thoroughly commented. The location where you insert the code you wish to check is in the Update method found in Game1.cs. The default that I put in is a line of code that generates a new Guid using Guid.NewGuid (which, if you’re curious, does not create any heap allocations). Read all of the comments in the Update method (at the very least) to make sure that your code is measured properly. It’s important to make sure that you meaningfully reference any thing you create after the second call to get the memory or else (in Release configuration at least) you will likely get incorrect results. Anyway, it should make sense when you read the comments and if not, feel free to post a comment here or ask me on Twitter. You can find my utilities and code samples page here: http://www.bobtacoindustries.com/developers/utils/Default.aspx To download CheckMemoryAllocationGame’s source code directly: http://www.bobtacoindustries.com/developers/utils/CheckMemoryAllocationGame.zip (If you’re looking to do this outside of the context of an XNA game, the measurement code in the Update method can easily be adapted into, e.g., a C# Windows Console application. In the past I mostly did that, actually. But I didn’t feel like adding references to all the XNA assemblies this time and… anyway, if you want you can easily convert it to a console application. If there’s any demand for it, I’ll do it myself and update this post when I get a chance.)

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  • Which web site gives the most accurate indication of a programmer's capabilities?

    - by Jerry Coffin
    If you were hiring programmers, and could choose between one of (say) the top 100 coders on topcoder.com, or one of the top 100 on stackoverflow.com, which would you choose? At least to me, it would appear that topcoder.com gives a more objective evaluation of pure ability to solve problems and write code. At the same time, despite obvious technical capabilities, this person may lack any hint of social skills -- he may be purely a "lone coder", with little or no ability to help/work with others, may lack mentoring ability to help transfer his technical skills to others, etc. On the other hand, stackoverflow.com would at least appear to give a much better indication of peers' opinion of the coder in question, and the degree to which his presence and useful and helpful to others on the "team". At the same time, the scoring system is such that somebody who just throws up a lot of mediocre (or even poor answers) will almost inevitably accumulate a positive total of "reputation" points -- a single up-vote (perhaps just out of courtesy) will counteract the effects of no fewer than 5 down-votes, and others are discouraged (to some degree) from down-voting because they have to sacrifice their own reputation points to do so. At the same time, somebody who makes little or no technical contribution seems unlikely to accumulate a reputation that lands them (even close to) the top of the heap, so to speak. So, which provides a more useful indication of the degree to which this particular coder is likely to be useful to your organization? If you could choose between them, which set of coders would you rather have working on your team?

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  • Oh snap! My RPi was upgraded to 512MB! Woo-hoo!

    - by hinkmond
    I ordered a Raspberry Pi Model B (256MB) over 4 months ago on backorder. When it finally came I saw it was upgraded to the new half a gig model! Woot! But, all was not perfect. Gary C. told me the shipped configuration of the new RPi models didn't have the right firmware for 512MB, and I had to upgrade the start.elf in the /boot directory to recognize all of the 512MB RAM. I did a "free" command, and sure enough saw only 240MB. Sadness. But, Gary gave me a copy of his start.elf which worked after some trail and error. For anyone ordering the new RPi Model B w/512MB, here are the steps to get you going with full 512MB RAM: sudo apt-get update --fix-missing sudo apt-get upgrade --fix-missing # NOTE: This step takes at least a couple hours on a # fast network wget https://raw.github.com/raspberrypi/firmware/\ 164b0fe2b3b56081c7510df93bc1440aebe45f7e/boot/\ arm496_start.elf sudo mv /boot/start.elf /boot/orig-start.elf sudo mv arm496_start.elf /boot/start.elf sudo reboot free total used free shared buffers cached Mem: 497768 210596 287172 0 16892 169624 -/+ buffers/cache: 24080 473688 Swap: 102396 0 102396 So of course this means... (drumroll) there is now 498MB available for the Java Embedded heap! java -Xmx400m -version java version "1.7.0_06" Java(TM) SE Embedded Runtime Environment (build 1.7.0_06-b24, headless) Java HotSpot(TM) Embedded Client VM (build 23.2-b09, mixed mode) Yeah, baby! Hinkmond

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  • Dealing with numerous, simultaneous sounds in unity

    - by luxchar
    I've written a custom class that creates a fixed number of audio sources. When a new sound is played, it goes through the class, which creates a queue of sounds that will be played during that frame. The sounds that are closer to the camera are given preference. If new sounds arrive in the next frame, I have a complex set of rules that determines how to replace the old ones. Ideally, "big" or "important" sounds should not be replaced by small ones. Sound replacement is necessary since the game can be fast-paced at times, and should try to play new sounds by replacing old ones. Otherwise, there can be "silent" moments when an old sound is about to stop playing and isn't replaced right away by a new sound. The drawback of replacing old sounds right away is that there is a harsh transition from the old sound clip to the new one. But I wonder if I could just remove that management logic altogether, and create audio sources on the fly for new sounds. I could give "important" sounds more priority (closer to 0 in the corresponding property) as opposed to less important ones, and let Unity take care of culling out sound effects that exceed the channel limit. The only drawback is that it requires many heap allocations. I wonder what strategy people use here?

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  • Impact of Server Failure on Coherence Request Processing

    - by jpurdy
    Requests against a given cache server may be temporarily blocked for several seconds following the failure of other cluster members. This may cause issues for applications that can not tolerate multi-second response times even during failover processing (ignoring for the moment that in practice there are a variety of issues that make such absolute guarantees challenging even when there are no server failures). In general, Coherence is designed around the principle that failures in one member should not affect the rest of the cluster if at all possible. However, it's obvious that if that failed member was managing a piece of state that another member depends on, the second member will need to wait until a new member assumes responsibility for managing that state. This transfer of responsibility is (as of Coherence 3.7) performed by the primary service thread for each cache service. The finest possible granularity for transferring responsibility is a single partition. So the question becomes how to minimize the time spent processing each partition. Here are some optimizations that may reduce this period: Reduce the size of each partition (by increasing the partition count) Increase the number of JVMs across the cluster (increasing the total number of primary service threads) Increase the number of CPUs across the cluster (making sure that each JVM has a CPU core when needed) Re-evaluate the set of configured indexes (as these will need to be rebuilt when a partition moves) Make sure that the backing map is as fast as possible (in most cases this means running on-heap) Make sure that the cluster is running on hardware with fast CPU cores (since the partition processing is single-threaded) As always, proper testing is required to make sure that configuration changes have the desired effect (and also to quantify that effect).

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  • When and how does one become a good programmer these days? [closed]

    - by YoungMoney
    I mean, good enough to make software people want and get paid for it. Maybe even good enough to launch a company or something. I'm also concerned that I'm not applying the finer points of my algorithms/data structures/software design knowledge. Background: I'm 20 and have been struggling with programming for about two years now, trying to become a software engineer. I started with a few university courses that I did quite poorly in. I learned how to make websites with HTML/JavaScript and PHP/MySQL, but feel like I know very relevant theory for making good databases - how does something like Facebook serve hundreds of millions of people? What would be smart ways to store data? I don't know. Now I'm doing some android application development, but again I have no idea about good Java design theory (I use static variables like they're going out of fashion) and feel more like I'm gluing stuff together and letting Eclipse slowly autocomplete my project. In short, I'm not sure if I'm becoming a legitimate software developer or just "doing what's cool". At least I've taken some data structures and Algorithms courses and plan to take more in the next years. But I'm having a really tough time applying this stuff to my fun little apps that I'm building. Every language higher level than C++ seems to have its own quicksort function already built-in, for example. Similarly, I can't remember ever needing to implement a linked-list, heap, binary tree, or or worry about pointers and memory management. But maybe this is a good thing so that I focus on other things? I'm not too sure what those other things are though. Hopefully something more than building another photo sharing app. Anyways that's it for me, I look forward to your responses!

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  • Where can these be posted besides the Python Cookbook?

    - by Noctis Skytower
    Whitespace Assembler #! /usr/bin/env python """Assembler.py Compiles a program from "Assembly" folder into "Program" folder. Can be executed directly by double-click or on the command line. Give name of *.WSA file without extension (example: stack_calc).""" ################################################################################ __author__ = 'Stephen "Zero" Chappell <[email protected]>' __date__ = '14 March 2010' __version__ = '$Revision: 3 $' ################################################################################ import string from Interpreter import INS, MNEMONIC ################################################################################ def parse(code): program = [] process_virtual(program, code) process_control(program) return tuple(program) def process_virtual(program, code): for line, text in enumerate(code.split('\n')): if not text or text[0] == '#': continue if text.startswith('part '): parse_part(program, line, text[5:]) elif text.startswith(' '): parse_code(program, line, text[5:]) else: syntax_error(line) def syntax_error(line): raise SyntaxError('Line ' + str(line + 1)) ################################################################################ def process_control(program): parts = get_parts(program) names = dict(pair for pair in zip(parts, generate_index())) correct_control(program, names) def get_parts(program): parts = [] for ins in program: if isinstance(ins, tuple): ins, arg = ins if ins == INS.PART: if arg in parts: raise NameError('Part definition was found twice: ' + arg) parts.append(arg) return parts def generate_index(): index = 1 while True: yield index index *= -1 if index > 0: index += 1 def correct_control(program, names): for index, ins in enumerate(program): if isinstance(ins, tuple): ins, arg = ins if ins in HAS_LABEL: if arg not in names: raise NameError('Part definition was never found: ' + arg) program[index] = (ins, names[arg]) ################################################################################ def parse_part(program, line, text): if not valid_label(text): syntax_error(line) program.append((INS.PART, text)) def valid_label(text): if not between_quotes(text): return False label = text[1:-1] if not valid_name(label): return False return True def between_quotes(text): if len(text) < 3: return False if text.count('"') != 2: return False if text[0] != '"' or text[-1] != '"': return False return True def valid_name(label): valid_characters = string.ascii_letters + string.digits + '_' valid_set = frozenset(valid_characters) label_set = frozenset(label) if len(label_set - valid_set) != 0: return False return True ################################################################################ from Interpreter import HAS_LABEL, Program NO_ARGS = Program.NO_ARGS HAS_ARG = Program.HAS_ARG TWO_WAY = tuple(set(NO_ARGS) & set(HAS_ARG)) ################################################################################ def parse_code(program, line, text): for ins, word in enumerate(MNEMONIC): if text.startswith(word): check_code(program, line, text[len(word):], ins) break else: syntax_error(line) def check_code(program, line, text, ins): if ins in TWO_WAY: if text: number = parse_number(line, text) program.append((ins, number)) else: program.append(ins) elif ins in HAS_LABEL: text = parse_label(line, text) program.append((ins, text)) elif ins in HAS_ARG: number = parse_number(line, text) program.append((ins, number)) elif ins in NO_ARGS: if text: syntax_error(line) program.append(ins) else: syntax_error(line) def parse_label(line, text): if not text or text[0] != ' ': syntax_error(line) text = text[1:] if not valid_label(text): syntax_error(line) return text ################################################################################ def parse_number(line, text): if not valid_number(text): syntax_error(line) return int(text) def valid_number(text): if len(text) < 2: return False if text[0] != ' ': return False text = text[1:] if '+' in text and '-' in text: return False if '+' in text: if text.count('+') != 1: return False if text[0] != '+': return False text = text[1:] if not text: return False if '-' in text: if text.count('-') != 1: return False if text[0] != '-': return False text = text[1:] if not text: return False valid_set = frozenset(string.digits) value_set = frozenset(text) if len(value_set - valid_set) != 0: return False return True ################################################################################ ################################################################################ from Interpreter import partition_number VMC_2_TRI = { (INS.PUSH, True): (0, 0), (INS.COPY, False): (0, 2, 0), (INS.COPY, True): (0, 1, 0), (INS.SWAP, False): (0, 2, 1), (INS.AWAY, False): (0, 2, 2), (INS.AWAY, True): (0, 1, 2), (INS.ADD, False): (1, 0, 0, 0), (INS.SUB, False): (1, 0, 0, 1), (INS.MUL, False): (1, 0, 0, 2), (INS.DIV, False): (1, 0, 1, 0), (INS.MOD, False): (1, 0, 1, 1), (INS.SET, False): (1, 1, 0), (INS.GET, False): (1, 1, 1), (INS.PART, True): (2, 0, 0), (INS.CALL, True): (2, 0, 1), (INS.GOTO, True): (2, 0, 2), (INS.ZERO, True): (2, 1, 0), (INS.LESS, True): (2, 1, 1), (INS.BACK, False): (2, 1, 2), (INS.EXIT, False): (2, 2, 2), (INS.OCHR, False): (1, 2, 0, 0), (INS.OINT, False): (1, 2, 0, 1), (INS.ICHR, False): (1, 2, 1, 0), (INS.IINT, False): (1, 2, 1, 1) } ################################################################################ def to_trinary(program): trinary_code = [] for ins in program: if isinstance(ins, tuple): ins, arg = ins trinary_code.extend(VMC_2_TRI[(ins, True)]) trinary_code.extend(from_number(arg)) else: trinary_code.extend(VMC_2_TRI[(ins, False)]) return tuple(trinary_code) def from_number(arg): code = [int(arg < 0)] if arg: for bit in reversed(list(partition_number(abs(arg), 2))): code.append(bit) return code + [2] return code + [0, 2] to_ws = lambda trinary: ''.join(' \t\n'[index] for index in trinary) def compile_wsa(source): program = parse(source) trinary = to_trinary(program) ws_code = to_ws(trinary) return ws_code ################################################################################ ################################################################################ import os import sys import time import traceback def main(): name, source, command_line, error = get_source() if not error: start = time.clock() try: ws_code = compile_wsa(source) except: print('ERROR: File could not be compiled.\n') traceback.print_exc() error = True else: path = os.path.join('Programs', name + '.ws') try: open(path, 'w').write(ws_code) except IOError as err: print(err) error = True else: div, mod = divmod((time.clock() - start) * 1000, 1) args = int(div), '{:.3}'.format(mod)[1:] print('DONE: Comipled in {}{} ms'.format(*args)) handle_close(error, command_line) def get_source(): if len(sys.argv) > 1: command_line = True name = sys.argv[1] else: command_line = False try: name = input('Source File: ') except: return None, None, False, True print() path = os.path.join('Assembly', name + '.wsa') try: return name, open(path).read(), command_line, False except IOError as err: print(err) return None, None, command_line, True def handle_close(error, command_line): if error: usage = 'Usage: {} <assembly>'.format(os.path.basename(sys.argv[0])) print('\n{}\n{}'.format('-' * len(usage), usage)) if not command_line: time.sleep(10) ################################################################################ if __name__ == '__main__': main() Whitespace Helpers #! /usr/bin/env python """Helpers.py Includes a function to encode Python strings into my WSA format. Has a "PRINT_LINE" function that can be copied to a WSA program. Contains a "PRINT" function and documentation as an explanation.""" ################################################################################ __author__ = 'Stephen "Zero" Chappell <[email protected]>' __date__ = '14 March 2010' __version__ = '$Revision: 1 $' ################################################################################ def encode_string(string, addr): print(' push', addr) print(' push', len(string)) print(' set') addr += 1 for offset, character in enumerate(string): print(' push', addr + offset) print(' push', ord(character)) print(' set') ################################################################################ # Prints a string with newline. # push addr # call "PRINT_LINE" """ part "PRINT_LINE" call "PRINT" push 10 ochr back """ ################################################################################ # def print(array): # if len(array) <= 0: # return # offset = 1 # while len(array) - offset >= 0: # ptr = array.ptr + offset # putch(array[ptr]) # offset += 1 """ part "PRINT" # Line 1-2 copy get less "__PRINT_RET_1" copy get zero "__PRINT_RET_1" # Line 3 push 1 # Line 4 part "__PRINT_LOOP" copy copy 2 get swap sub less "__PRINT_RET_2" # Line 5 copy 1 copy 1 add # Line 6 get ochr # Line 7 push 1 add goto "__PRINT_LOOP" part "__PRINT_RET_2" away part "__PRINT_RET_1" away back """ Whitespace Interpreter #! /usr/bin/env python """Interpreter.py Runs programs in "Programs" and creates *.WSO files when needed. Can be executed directly by double-click or on the command line. If run on command line, add "ASM" flag to dump program assembly.""" ################################################################################ __author__ = 'Stephen "Zero" Chappell <[email protected]>' __date__ = '14 March 2010' __version__ = '$Revision: 4 $' ################################################################################ def test_file(path): disassemble(parse(trinary(load(path))), True) ################################################################################ load = lambda ws: ''.join(c for r in open(ws) for c in r if c in ' \t\n') trinary = lambda ws: tuple(' \t\n'.index(c) for c in ws) ################################################################################ def enum(names): names = names.replace(',', ' ').split() space = dict((reversed(pair) for pair in enumerate(names)), __slots__=()) return type('enum', (object,), space)() INS = enum('''\ PUSH, COPY, SWAP, AWAY, \ ADD, SUB, MUL, DIV, MOD, \ SET, GET, \ PART, CALL, GOTO, ZERO, LESS, BACK, EXIT, \ OCHR, OINT, ICHR, IINT''') ################################################################################ def parse(code): ins = iter(code).__next__ program = [] while True: try: imp = ins() except StopIteration: return tuple(program) if imp == 0: # [Space] parse_stack(ins, program) elif imp == 1: # [Tab] imp = ins() if imp == 0: # [Tab][Space] parse_math(ins, program) elif imp == 1: # [Tab][Tab] parse_heap(ins, program) else: # [Tab][Line] parse_io(ins, program) else: # [Line] parse_flow(ins, program) def parse_number(ins): sign = ins() if sign == 2: raise StopIteration() buffer = '' code = ins() if code == 2: raise StopIteration() while code != 2: buffer += str(code) code = ins() if sign == 1: return int(buffer, 2) * -1 return int(buffer, 2) ################################################################################ def parse_stack(ins, program): code = ins() if code == 0: # [Space] number = parse_number(ins) program.append((INS.PUSH, number)) elif code == 1: # [Tab] code = ins() number = parse_number(ins) if code == 0: # [Tab][Space] program.append((INS.COPY, number)) elif code == 1: # [Tab][Tab] raise StopIteration() else: # [Tab][Line] program.append((INS.AWAY, number)) else: # [Line] code = ins() if code == 0: # [Line][Space] program.append(INS.COPY) elif code == 1: # [Line][Tab] program.append(INS.SWAP) else: # [Line][Line] program.append(INS.AWAY) def parse_math(ins, program): code = ins() if code == 0: # [Space] code = ins() if code == 0: # [Space][Space] program.append(INS.ADD) elif code == 1: # [Space][Tab] program.append(INS.SUB) else: # [Space][Line] program.append(INS.MUL) elif code == 1: # [Tab] code = ins() if code == 0: # [Tab][Space] program.append(INS.DIV) elif code == 1: # [Tab][Tab] program.append(INS.MOD) else: # [Tab][Line] raise StopIteration() else: # [Line] raise StopIteration() def parse_heap(ins, program): code = ins() if code == 0: # [Space] program.append(INS.SET) elif code == 1: # [Tab] program.append(INS.GET) else: # [Line] raise StopIteration() def parse_io(ins, program): code = ins() if code == 0: # [Space] code = ins() if code == 0: # [Space][Space] program.append(INS.OCHR) elif code == 1: # [Space][Tab] program.append(INS.OINT) else: # [Space][Line] raise StopIteration() elif code == 1: # [Tab] code = ins() if code == 0: # [Tab][Space] program.append(INS.ICHR) elif code == 1: # [Tab][Tab] program.append(INS.IINT) else: # [Tab][Line] raise StopIteration() else: # [Line] raise StopIteration() def parse_flow(ins, program): code = ins() if code == 0: # [Space] code = ins() label = parse_number(ins) if code == 0: # [Space][Space] program.append((INS.PART, label)) elif code == 1: # [Space][Tab] program.append((INS.CALL, label)) else: # [Space][Line] program.append((INS.GOTO, label)) elif code == 1: # [Tab] code = ins() if code == 0: # [Tab][Space] label = parse_number(ins) program.append((INS.ZERO, label)) elif code == 1: # [Tab][Tab] label = parse_number(ins) program.append((INS.LESS, label)) else: # [Tab][Line] program.append(INS.BACK) else: # [Line] code = ins() if code == 2: # [Line][Line] program.append(INS.EXIT) else: # [Line][Space] or [Line][Tab] raise StopIteration() ################################################################################ MNEMONIC = '\ push copy swap away add sub mul div mod set get part \ call goto zero less back exit ochr oint ichr iint'.split() HAS_ARG = [getattr(INS, name) for name in 'PUSH COPY AWAY PART CALL GOTO ZERO LESS'.split()] HAS_LABEL = [getattr(INS, name) for name in 'PART CALL GOTO ZERO LESS'.split()] def disassemble(program, names=False): if names: names = create_names(program) for ins in program: if isinstance(ins, tuple): ins, arg = ins assert ins in HAS_ARG has_arg = True else: assert INS.PUSH <= ins <= INS.IINT has_arg = False if ins == INS.PART: if names: print(MNEMONIC[ins], '"' + names[arg] + '"') else: print(MNEMONIC[ins], arg) elif has_arg and ins in HAS_ARG: if ins in HAS_LABEL and names: assert arg in names print(' ' + MNEMONIC[ins], '"' + names[arg] + '"') else: print(' ' + MNEMONIC[ins], arg) else: print(' ' + MNEMONIC[ins]) ################################################################################ def create_names(program): names = {} number = 1 for ins in program: if isinstance(ins, tuple) and ins[0] == INS.PART: label = ins[1] assert label not in names names[label] = number_to_name(number) number += 1 return names def number_to_name(number): name = '' for offset in reversed(list(partition_number(number, 27))): if offset: name += chr(ord('A') + offset - 1) else: name += '_' return name def partition_number(number, base): div, mod = divmod(number, base) yield mod while div: div, mod = divmod(div, base) yield mod ################################################################################ CODE = (' \t\n', ' \n ', ' \t \t\n', ' \n\t', ' \n\n', ' \t\n \t\n', '\t ', '\t \t', '\t \n', '\t \t ', '\t \t\t', '\t\t ', '\t\t\t', '\n \t\n', '\n \t \t\n', '\n \n \t\n', '\n\t \t\n', '\n\t\t \t\n', '\n\t\n', '\n\n\n', '\t\n ', '\t\n \t', '\t\n\t ', '\t\n\t\t') EXAMPLE = ''.join(CODE) ################################################################################ NOTES = '''\ STACK ===== push number copy copy number swap away away number MATH ==== add sub mul div mod HEAP ==== set get FLOW ==== part label call label goto label zero label less label back exit I/O === ochr oint ichr iint''' ################################################################################ ################################################################################ class Stack: def __init__(self): self.__data = [] # Stack Operators def push(self, number): self.__data.append(number) def copy(self, number=None): if number is None: self.__data.append(self.__data[-1]) else: size = len(self.__data) index = size - number - 1 assert 0 <= index < size self.__data.append(self.__data[index]) def swap(self): self.__data[-2], self.__data[-1] = self.__data[-1], self.__data[-2] def away(self, number=None): if number is None: self.__data.pop() else: size = len(self.__data) index = size - number - 1 assert 0 <= index < size del self.__data[index:-1] # Math Operators def add(self): suffix = self.__data.pop() prefix = self.__data.pop() self.__data.append(prefix + suffix) def sub(self): suffix = self.__data.pop() prefix = self.__data.pop() self.__data.append(prefix - suffix) def mul(self): suffix = self.__data.pop() prefix = self.__data.pop() self.__data.append(prefix * suffix) def div(self): suffix = self.__data.pop() prefix = self.__data.pop() self.__data.append(prefix // suffix) def mod(self): suffix = self.__data.pop() prefix = self.__data.pop() self.__data.append(prefix % suffix) # Program Operator def pop(self): return self.__data.pop() ################################################################################ class Heap: def __init__(self): self.__data = {} def set_(self, addr, item): if item: self.__data[addr] = item elif addr in self.__data: del self.__data[addr] def get_(self, addr): return self.__data.get(addr, 0) ################################################################################ import os import zlib import msvcrt import pickle import string class CleanExit(Exception): pass NOP = lambda arg: None DEBUG_WHITESPACE = False ################################################################################ class Program: NO_ARGS = INS.COPY, INS.SWAP, INS.AWAY, INS.ADD, \ INS.SUB, INS.MUL, INS.DIV, INS.MOD, \ INS.SET, INS.GET, INS.BACK, INS.EXIT, \ INS.OCHR, INS.OINT, INS.ICHR, INS.IINT HAS_ARG = INS.PUSH, INS.COPY, INS.AWAY, INS.PART, \ INS.CALL, INS.GOTO, INS.ZERO, INS.LESS def __init__(self, code): self.__data = code self.__validate() self.__build_jump() self.__check_jump() self.__setup_exec() def __setup_exec(self): self.__iptr = 0 self.__stck = stack = Stack() self.__heap = Heap() self.__cast = [] self.__meth = (stack.push, stack.copy, stack.swap, stack.away, stack.add, stack.sub, stack.mul, stack.div, stack.mod, self.__set, self.__get, NOP, self.__call, self.__goto, self.__zero, self.__less, self.__back, self.__exit, self.__ochr, self.__oint, self.__ichr, self.__iint) def step(self): ins = self.__data[self.__iptr] self.__iptr += 1 if isinstance(ins, tuple): self.__meth[ins[0]](ins[1]) else: self.__meth[ins]() def run(self): while True: ins = self.__data[self.__iptr] self.__iptr += 1 if isinstance(ins, tuple): self.__meth[ins[0]](ins[1]) else: self.__meth[ins]() def __oint(self): for digit in str(self.__stck.pop()): msvcrt.putwch(digit) def __ichr(self): addr = self.__stck.pop() # Input Routine while msvcrt.kbhit(): msvcrt.getwch() while True: char = msvcrt.getwch() if char in '\x00\xE0': msvcrt.getwch() elif char in string.printable: char = char.replace('\r', '\n') msvcrt.putwch(char) break item = ord(char) # Storing Number self.__heap.set_(addr, item) def __iint(self): addr = self.__stck.pop() # Input Routine while msvcrt.kbhit(): msvcrt.getwch() buff = '' char = msvcrt.getwch() while char != '\r' or not buff: if char in '\x00\xE0': msvcrt.getwch() elif char in '+-' and not buff: msvcrt.putwch(char) buff += char elif '0' <= char <= '9': msvcrt.putwch(char) buff += char elif char == '\b': if buff: buff = buff[:-1] msvcrt.putwch(char) msvcrt.putwch(' ') msvcrt.putwch(char) char = msvcrt.getwch() msvcrt.putwch(char) msvcrt.putwch('\n') item = int(buff) # Storing Number self.__heap.set_(addr, item) def __goto(self, label): self.__iptr = self.__jump[label] def __zero(self, label): if self.__stck.pop() == 0: self.__iptr = self.__jump[label] def __less(self, label): if self.__stck.pop() < 0: self.__iptr = self.__jump[label] def __exit(self): self.__setup_exec() raise CleanExit() def __set(self): item = self.__stck.pop() addr = self.__stck.po

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  • top tweets WebLogic Partner Community – June 2012

    - by JuergenKress
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  • Beware Sneaky Reads with Unique Indexes

    - by Paul White NZ
    A few days ago, Sandra Mueller (twitter | blog) asked a question using twitter’s #sqlhelp hash tag: “Might SQL Server retrieve (out-of-row) LOB data from a table, even if the column isn’t referenced in the query?” Leaving aside trivial cases (like selecting a computed column that does reference the LOB data), one might be tempted to say that no, SQL Server does not read data you haven’t asked for.  In general, that’s quite correct; however there are cases where SQL Server might sneakily retrieve a LOB column… Example Table Here’s a T-SQL script to create that table and populate it with 1,000 rows: CREATE TABLE dbo.LOBtest ( pk INTEGER IDENTITY NOT NULL, some_value INTEGER NULL, lob_data VARCHAR(MAX) NULL, another_column CHAR(5) NULL, CONSTRAINT [PK dbo.LOBtest pk] PRIMARY KEY CLUSTERED (pk ASC) ); GO DECLARE @Data VARCHAR(MAX); SET @Data = REPLICATE(CONVERT(VARCHAR(MAX), 'x'), 65540);   WITH Numbers (n) AS ( SELECT ROW_NUMBER() OVER (ORDER BY (SELECT 0)) FROM master.sys.columns C1, master.sys.columns C2 ) INSERT LOBtest WITH (TABLOCKX) ( some_value, lob_data ) SELECT TOP (1000) N.n, @Data FROM Numbers N WHERE N.n <= 1000; Test 1: A Simple Update Let’s run a query to subtract one from every value in the some_value column: UPDATE dbo.LOBtest WITH (TABLOCKX) SET some_value = some_value - 1; As you might expect, modifying this integer column in 1,000 rows doesn’t take very long, or use many resources.  The STATITICS IO and TIME output shows a total of 9 logical reads, and 25ms elapsed time.  The query plan is also very simple: Looking at the Clustered Index Scan, we can see that SQL Server only retrieves the pk and some_value columns during the scan: The pk column is needed by the Clustered Index Update operator to uniquely identify the row that is being changed.  The some_value column is used by the Compute Scalar to calculate the new value.  (In case you are wondering what the Top operator is for, it is used to enforce SET ROWCOUNT). Test 2: Simple Update with an Index Now let’s create a nonclustered index keyed on the some_value column, with lob_data as an included column: CREATE NONCLUSTERED INDEX [IX dbo.LOBtest some_value (lob_data)] ON dbo.LOBtest (some_value) INCLUDE ( lob_data ) WITH ( FILLFACTOR = 100, MAXDOP = 1, SORT_IN_TEMPDB = ON ); This is not a useful index for our simple update query; imagine that someone else created it for a different purpose.  Let’s run our update query again: UPDATE dbo.LOBtest WITH (TABLOCKX) SET some_value = some_value - 1; We find that it now requires 4,014 logical reads and the elapsed query time has increased to around 100ms.  The extra logical reads (4 per row) are an expected consequence of maintaining the nonclustered index. The query plan is very similar to before (click to enlarge): The Clustered Index Update operator picks up the extra work of maintaining the nonclustered index. The new Compute Scalar operators detect whether the value in the some_value column has actually been changed by the update.  SQL Server may be able to skip maintaining the nonclustered index if the value hasn’t changed (see my previous post on non-updating updates for details).  Our simple query does change the value of some_data in every row, so this optimization doesn’t add any value in this specific case. The output list of columns from the Clustered Index Scan hasn’t changed from the one shown previously: SQL Server still just reads the pk and some_data columns.  Cool. Overall then, adding the nonclustered index hasn’t had any startling effects, and the LOB column data still isn’t being read from the table.  Let’s see what happens if we make the nonclustered index unique. Test 3: Simple Update with a Unique Index Here’s the script to create a new unique index, and drop the old one: CREATE UNIQUE NONCLUSTERED INDEX [UQ dbo.LOBtest some_value (lob_data)] ON dbo.LOBtest (some_value) INCLUDE ( lob_data ) WITH ( FILLFACTOR = 100, MAXDOP = 1, SORT_IN_TEMPDB = ON ); GO DROP INDEX [IX dbo.LOBtest some_value (lob_data)] ON dbo.LOBtest; Remember that SQL Server only enforces uniqueness on index keys (the some_data column).  The lob_data column is simply stored at the leaf-level of the non-clustered index.  With that in mind, we might expect this change to make very little difference.  Let’s see: UPDATE dbo.LOBtest WITH (TABLOCKX) SET some_value = some_value - 1; Whoa!  Now look at the elapsed time and logical reads: Scan count 1, logical reads 2016, physical reads 0, read-ahead reads 0, lob logical reads 36015, lob physical reads 0, lob read-ahead reads 15992.   CPU time = 172 ms, elapsed time = 16172 ms. Even with all the data and index pages in memory, the query took over 16 seconds to update just 1,000 rows, performing over 52,000 LOB logical reads (nearly 16,000 of those using read-ahead). Why on earth is SQL Server reading LOB data in a query that only updates a single integer column? The Query Plan The query plan for test 3 looks a bit more complex than before: In fact, the bottom level is exactly the same as we saw with the non-unique index.  The top level has heaps of new stuff though, which I’ll come to in a moment. You might be expecting to find that the Clustered Index Scan is now reading the lob_data column (for some reason).  After all, we need to explain where all the LOB logical reads are coming from.  Sadly, when we look at the properties of the Clustered Index Scan, we see exactly the same as before: SQL Server is still only reading the pk and some_value columns – so what’s doing the LOB reads? Updates that Sneakily Read Data We have to go as far as the Clustered Index Update operator before we see LOB data in the output list: [Expr1020] is a bit flag added by an earlier Compute Scalar.  It is set true if the some_value column has not been changed (part of the non-updating updates optimization I mentioned earlier). The Clustered Index Update operator adds two new columns: the lob_data column, and some_value_OLD.  The some_value_OLD column, as the name suggests, is the pre-update value of the some_value column.  At this point, the clustered index has already been updated with the new value, but we haven’t touched the nonclustered index yet. An interesting observation here is that the Clustered Index Update operator can read a column into the data flow as part of its update operation.  SQL Server could have read the LOB data as part of the initial Clustered Index Scan, but that would mean carrying the data through all the operations that occur prior to the Clustered Index Update.  The server knows it will have to go back to the clustered index row to update it, so it delays reading the LOB data until then.  Sneaky! Why the LOB Data Is Needed This is all very interesting (I hope), but why is SQL Server reading the LOB data?  For that matter, why does it need to pass the pre-update value of the some_value column out of the Clustered Index Update? The answer relates to the top row of the query plan for test 3.  I’ll reproduce it here for convenience: Notice that this is a wide (per-index) update plan.  SQL Server used a narrow (per-row) update plan in test 2, where the Clustered Index Update took care of maintaining the nonclustered index too.  I’ll talk more about this difference shortly. The Split/Sort/Collapse combination is an optimization, which aims to make per-index update plans more efficient.  It does this by breaking each update into a delete/insert pair, reordering the operations, removing any redundant operations, and finally applying the net effect of all the changes to the nonclustered index. Imagine we had a unique index which currently holds three rows with the values 1, 2, and 3.  If we run a query that adds 1 to each row value, we would end up with values 2, 3, and 4.  The net effect of all the changes is the same as if we simply deleted the value 1, and added a new value 4. By applying net changes, SQL Server can also avoid false unique-key violations.  If we tried to immediately update the value 1 to a 2, it would conflict with the existing value 2 (which would soon be updated to 3 of course) and the query would fail.  You might argue that SQL Server could avoid the uniqueness violation by starting with the highest value (3) and working down.  That’s fine, but it’s not possible to generalize this logic to work with every possible update query. SQL Server has to use a wide update plan if it sees any risk of false uniqueness violations.  It’s worth noting that the logic SQL Server uses to detect whether these violations are possible has definite limits.  As a result, you will often receive a wide update plan, even when you can see that no violations are possible. Another benefit of this optimization is that it includes a sort on the index key as part of its work.  Processing the index changes in index key order promotes sequential I/O against the nonclustered index. A side-effect of all this is that the net changes might include one or more inserts.  In order to insert a new row in the index, SQL Server obviously needs all the columns – the key column and the included LOB column.  This is the reason SQL Server reads the LOB data as part of the Clustered Index Update. In addition, the some_value_OLD column is required by the Split operator (it turns updates into delete/insert pairs).  In order to generate the correct index key delete operation, it needs the old key value. The irony is that in this case the Split/Sort/Collapse optimization is anything but.  Reading all that LOB data is extremely expensive, so it is sad that the current version of SQL Server has no way to avoid it. Finally, for completeness, I should mention that the Filter operator is there to filter out the non-updating updates. Beating the Set-Based Update with a Cursor One situation where SQL Server can see that false unique-key violations aren’t possible is where it can guarantee that only one row is being updated.  Armed with this knowledge, we can write a cursor (or the WHILE-loop equivalent) that updates one row at a time, and so avoids reading the LOB data: SET NOCOUNT ON; SET STATISTICS XML, IO, TIME OFF;   DECLARE @PK INTEGER, @StartTime DATETIME; SET @StartTime = GETUTCDATE();   DECLARE curUpdate CURSOR LOCAL FORWARD_ONLY KEYSET SCROLL_LOCKS FOR SELECT L.pk FROM LOBtest L ORDER BY L.pk ASC;   OPEN curUpdate;   WHILE (1 = 1) BEGIN FETCH NEXT FROM curUpdate INTO @PK;   IF @@FETCH_STATUS = -1 BREAK; IF @@FETCH_STATUS = -2 CONTINUE;   UPDATE dbo.LOBtest SET some_value = some_value - 1 WHERE CURRENT OF curUpdate; END;   CLOSE curUpdate; DEALLOCATE curUpdate;   SELECT DATEDIFF(MILLISECOND, @StartTime, GETUTCDATE()); That completes the update in 1280 milliseconds (remember test 3 took over 16 seconds!) I used the WHERE CURRENT OF syntax there and a KEYSET cursor, just for the fun of it.  One could just as well use a WHERE clause that specified the primary key value instead. Clustered Indexes A clustered index is the ultimate index with included columns: all non-key columns are included columns in a clustered index.  Let’s re-create the test table and data with an updatable primary key, and without any non-clustered indexes: IF OBJECT_ID(N'dbo.LOBtest', N'U') IS NOT NULL DROP TABLE dbo.LOBtest; GO CREATE TABLE dbo.LOBtest ( pk INTEGER NOT NULL, some_value INTEGER NULL, lob_data VARCHAR(MAX) NULL, another_column CHAR(5) NULL, CONSTRAINT [PK dbo.LOBtest pk] PRIMARY KEY CLUSTERED (pk ASC) ); GO DECLARE @Data VARCHAR(MAX); SET @Data = REPLICATE(CONVERT(VARCHAR(MAX), 'x'), 65540);   WITH Numbers (n) AS ( SELECT ROW_NUMBER() OVER (ORDER BY (SELECT 0)) FROM master.sys.columns C1, master.sys.columns C2 ) INSERT LOBtest WITH (TABLOCKX) ( pk, some_value, lob_data ) SELECT TOP (1000) N.n, N.n, @Data FROM Numbers N WHERE N.n <= 1000; Now here’s a query to modify the cluster keys: UPDATE dbo.LOBtest SET pk = pk + 1; The query plan is: As you can see, the Split/Sort/Collapse optimization is present, and we also gain an Eager Table Spool, for Halloween protection.  In addition, SQL Server now has no choice but to read the LOB data in the Clustered Index Scan: The performance is not great, as you might expect (even though there is no non-clustered index to maintain): Table 'LOBtest'. Scan count 1, logical reads 2011, physical reads 0, read-ahead reads 0, lob logical reads 36015, lob physical reads 0, lob read-ahead reads 15992.   Table 'Worktable'. Scan count 1, logical reads 2040, physical reads 0, read-ahead reads 0, lob logical reads 34000, lob physical reads 0, lob read-ahead reads 8000.   SQL Server Execution Times: CPU time = 483 ms, elapsed time = 17884 ms. Notice how the LOB data is read twice: once from the Clustered Index Scan, and again from the work table in tempdb used by the Eager Spool. If you try the same test with a non-unique clustered index (rather than a primary key), you’ll get a much more efficient plan that just passes the cluster key (including uniqueifier) around (no LOB data or other non-key columns): A unique non-clustered index (on a heap) works well too: Both those queries complete in a few tens of milliseconds, with no LOB reads, and just a few thousand logical reads.  (In fact the heap is rather more efficient). There are lots more fun combinations to try that I don’t have space for here. Final Thoughts The behaviour shown in this post is not limited to LOB data by any means.  If the conditions are met, any unique index that has included columns can produce similar behaviour – something to bear in mind when adding large INCLUDE columns to achieve covering queries, perhaps. Paul White Email: [email protected] Twitter: @PaulWhiteNZ

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  • Understanding C# async / await (1) Compilation

    - by Dixin
    Now the async / await keywords are in C#. Just like the async and ! in F#, this new C# feature provides great convenience. There are many nice documents talking about how to use async / await in specific scenarios, like using async methods in ASP.NET 4.5 and in ASP.NET MVC 4, etc. In this article we will look at the real code working behind the syntax sugar. According to MSDN: The async modifier indicates that the method, lambda expression, or anonymous method that it modifies is asynchronous. Since lambda expression / anonymous method will be compiled to normal method, we will focus on normal async method. Preparation First of all, Some helper methods need to make up. internal class HelperMethods { internal static int Method(int arg0, int arg1) { // Do some IO. WebClient client = new WebClient(); Enumerable.Repeat("http://weblogs.asp.net/dixin", 10) .Select(client.DownloadString).ToArray(); int result = arg0 + arg1; return result; } internal static Task<int> MethodTask(int arg0, int arg1) { Task<int> task = new Task<int>(() => Method(arg0, arg1)); task.Start(); // Hot task (started task) should always be returned. return task; } internal static void Before() { } internal static void Continuation1(int arg) { } internal static void Continuation2(int arg) { } } Here Method() is a long running method doing some IO. Then MethodTask() wraps it into a Task and return that Task. Nothing special here. Await something in async method Since MethodTask() returns Task, let’s try to await it: internal class AsyncMethods { internal static async Task<int> MethodAsync(int arg0, int arg1) { int result = await HelperMethods.MethodTask(arg0, arg1); return result; } } Because we used await in the method, async must be put on the method. Now we get the first async method. According to the naming convenience, it is called MethodAsync. Of course a async method can be awaited. So we have a CallMethodAsync() to call MethodAsync(): internal class AsyncMethods { internal static async Task<int> CallMethodAsync(int arg0, int arg1) { int result = await MethodAsync(arg0, arg1); return result; } } After compilation, MethodAsync() and CallMethodAsync() becomes the same logic. This is the code of MethodAsyc(): internal class CompiledAsyncMethods { [DebuggerStepThrough] [AsyncStateMachine(typeof(MethodAsyncStateMachine))] // async internal static /*async*/ Task<int> MethodAsync(int arg0, int arg1) { MethodAsyncStateMachine methodAsyncStateMachine = new MethodAsyncStateMachine() { Arg0 = arg0, Arg1 = arg1, Builder = AsyncTaskMethodBuilder<int>.Create(), State = -1 }; methodAsyncStateMachine.Builder.Start(ref methodAsyncStateMachine); return methodAsyncStateMachine.Builder.Task; } } It just creates and starts a state machine MethodAsyncStateMachine: [CompilerGenerated] [StructLayout(LayoutKind.Auto)] internal struct MethodAsyncStateMachine : IAsyncStateMachine { public int State; public AsyncTaskMethodBuilder<int> Builder; public int Arg0; public int Arg1; public int Result; private TaskAwaiter<int> awaitor; void IAsyncStateMachine.MoveNext() { try { if (this.State != 0) { this.awaitor = HelperMethods.MethodTask(this.Arg0, this.Arg1).GetAwaiter(); if (!this.awaitor.IsCompleted) { this.State = 0; this.Builder.AwaitUnsafeOnCompleted(ref this.awaitor, ref this); return; } } else { this.State = -1; } this.Result = this.awaitor.GetResult(); } catch (Exception exception) { this.State = -2; this.Builder.SetException(exception); return; } this.State = -2; this.Builder.SetResult(this.Result); } [DebuggerHidden] void IAsyncStateMachine.SetStateMachine(IAsyncStateMachine param0) { this.Builder.SetStateMachine(param0); } } The generated code has been cleaned up so it is readable and can be compiled. Several things can be observed here: The async modifier is gone, which shows, unlike other modifiers (e.g. static), there is no such IL/CLR level “async” stuff. It becomes a AsyncStateMachineAttribute. This is similar to the compilation of extension method. The generated state machine is very similar to the state machine of C# yield syntax sugar. The local variables (arg0, arg1, result) are compiled to fields of the state machine. The real code (await HelperMethods.MethodTask(arg0, arg1)) is compiled into MoveNext(): HelperMethods.MethodTask(this.Arg0, this.Arg1).GetAwaiter(). CallMethodAsync() will create and start its own state machine CallMethodAsyncStateMachine: internal class CompiledAsyncMethods { [DebuggerStepThrough] [AsyncStateMachine(typeof(CallMethodAsyncStateMachine))] // async internal static /*async*/ Task<int> CallMethodAsync(int arg0, int arg1) { CallMethodAsyncStateMachine callMethodAsyncStateMachine = new CallMethodAsyncStateMachine() { Arg0 = arg0, Arg1 = arg1, Builder = AsyncTaskMethodBuilder<int>.Create(), State = -1 }; callMethodAsyncStateMachine.Builder.Start(ref callMethodAsyncStateMachine); return callMethodAsyncStateMachine.Builder.Task; } } CallMethodAsyncStateMachine has the same logic as MethodAsyncStateMachine above. The detail of the state machine will be discussed soon. Now it is clear that: async /await is a C# level syntax sugar. There is no difference to await a async method or a normal method. A method returning Task will be awaitable. State machine and continuation To demonstrate more details in the state machine, a more complex method is created: internal class AsyncMethods { internal static async Task<int> MultiCallMethodAsync(int arg0, int arg1, int arg2, int arg3) { HelperMethods.Before(); int resultOfAwait1 = await MethodAsync(arg0, arg1); HelperMethods.Continuation1(resultOfAwait1); int resultOfAwait2 = await MethodAsync(arg2, arg3); HelperMethods.Continuation2(resultOfAwait2); int resultToReturn = resultOfAwait1 + resultOfAwait2; return resultToReturn; } } In this method: There are multiple awaits. There are code before the awaits, and continuation code after each await After compilation, this multi-await method becomes the same as above single-await methods: internal class CompiledAsyncMethods { [DebuggerStepThrough] [AsyncStateMachine(typeof(MultiCallMethodAsyncStateMachine))] // async internal static /*async*/ Task<int> MultiCallMethodAsync(int arg0, int arg1, int arg2, int arg3) { MultiCallMethodAsyncStateMachine multiCallMethodAsyncStateMachine = new MultiCallMethodAsyncStateMachine() { Arg0 = arg0, Arg1 = arg1, Arg2 = arg2, Arg3 = arg3, Builder = AsyncTaskMethodBuilder<int>.Create(), State = -1 }; multiCallMethodAsyncStateMachine.Builder.Start(ref multiCallMethodAsyncStateMachine); return multiCallMethodAsyncStateMachine.Builder.Task; } } It creates and starts one single state machine, MultiCallMethodAsyncStateMachine: [CompilerGenerated] [StructLayout(LayoutKind.Auto)] internal struct MultiCallMethodAsyncStateMachine : IAsyncStateMachine { public int State; public AsyncTaskMethodBuilder<int> Builder; public int Arg0; public int Arg1; public int Arg2; public int Arg3; public int ResultOfAwait1; public int ResultOfAwait2; public int ResultToReturn; private TaskAwaiter<int> awaiter; void IAsyncStateMachine.MoveNext() { try { switch (this.State) { case -1: HelperMethods.Before(); this.awaiter = AsyncMethods.MethodAsync(this.Arg0, this.Arg1).GetAwaiter(); if (!this.awaiter.IsCompleted) { this.State = 0; this.Builder.AwaitUnsafeOnCompleted(ref this.awaiter, ref this); } break; case 0: this.ResultOfAwait1 = this.awaiter.GetResult(); HelperMethods.Continuation1(this.ResultOfAwait1); this.awaiter = AsyncMethods.MethodAsync(this.Arg2, this.Arg3).GetAwaiter(); if (!this.awaiter.IsCompleted) { this.State = 1; this.Builder.AwaitUnsafeOnCompleted(ref this.awaiter, ref this); } break; case 1: this.ResultOfAwait2 = this.awaiter.GetResult(); HelperMethods.Continuation2(this.ResultOfAwait2); this.ResultToReturn = this.ResultOfAwait1 + this.ResultOfAwait2; this.State = -2; this.Builder.SetResult(this.ResultToReturn); break; } } catch (Exception exception) { this.State = -2; this.Builder.SetException(exception); } } [DebuggerHidden] void IAsyncStateMachine.SetStateMachine(IAsyncStateMachine stateMachine) { this.Builder.SetStateMachine(stateMachine); } } The above code is already cleaned up, but there are still a lot of things. More clean up can be done, and the state machine can be very simple: [CompilerGenerated] [StructLayout(LayoutKind.Auto)] internal struct MultiCallMethodAsyncStateMachine : IAsyncStateMachine { // State: // -1: Begin // 0: 1st await is done // 1: 2nd await is done // ... // -2: End public int State; public TaskCompletionSource<int> ResultToReturn; // int resultToReturn ... public int Arg0; // int Arg0 public int Arg1; // int arg1 public int Arg2; // int arg2 public int Arg3; // int arg3 public int ResultOfAwait1; // int resultOfAwait1 ... public int ResultOfAwait2; // int resultOfAwait2 ... private Task<int> currentTaskToAwait; /// <summary> /// Moves the state machine to its next state. /// </summary> void IAsyncStateMachine.MoveNext() { try { switch (this.State) { // Orginal code is splitted by "case"s: // case -1: // HelperMethods.Before(); // MethodAsync(Arg0, arg1); // case 0: // int resultOfAwait1 = await ... // HelperMethods.Continuation1(resultOfAwait1); // MethodAsync(arg2, arg3); // case 1: // int resultOfAwait2 = await ... // HelperMethods.Continuation2(resultOfAwait2); // int resultToReturn = resultOfAwait1 + resultOfAwait2; // return resultToReturn; case -1: // -1 is begin. HelperMethods.Before(); // Code before 1st await. this.currentTaskToAwait = AsyncMethods.MethodAsync(this.Arg0, this.Arg1); // 1st task to await // When this.currentTaskToAwait is done, run this.MoveNext() and go to case 0. this.State = 0; IAsyncStateMachine this1 = this; // Cannot use "this" in lambda so create a local variable. this.currentTaskToAwait.ContinueWith(_ => this1.MoveNext()); // Callback break; case 0: // Now 1st await is done. this.ResultOfAwait1 = this.currentTaskToAwait.Result; // Get 1st await's result. HelperMethods.Continuation1(this.ResultOfAwait1); // Code after 1st await and before 2nd await. this.currentTaskToAwait = AsyncMethods.MethodAsync(this.Arg2, this.Arg3); // 2nd task to await // When this.currentTaskToAwait is done, run this.MoveNext() and go to case 1. this.State = 1; IAsyncStateMachine this2 = this; // Cannot use "this" in lambda so create a local variable. this.currentTaskToAwait.ContinueWith(_ => this2.MoveNext()); // Callback break; case 1: // Now 2nd await is done. this.ResultOfAwait2 = this.currentTaskToAwait.Result; // Get 2nd await's result. HelperMethods.Continuation2(this.ResultOfAwait2); // Code after 2nd await. int resultToReturn = this.ResultOfAwait1 + this.ResultOfAwait2; // Code after 2nd await. // End with resultToReturn. this.State = -2; // -2 is end. this.ResultToReturn.SetResult(resultToReturn); break; } } catch (Exception exception) { // End with exception. this.State = -2; // -2 is end. this.ResultToReturn.SetException(exception); } } /// <summary> /// Configures the state machine with a heap-allocated replica. /// </summary> /// <param name="stateMachine">The heap-allocated replica.</param> [DebuggerHidden] void IAsyncStateMachine.SetStateMachine(IAsyncStateMachine stateMachine) { // No core logic. } } Only Task and TaskCompletionSource are involved in this version. And MultiCallMethodAsync() can be simplified to: [DebuggerStepThrough] [AsyncStateMachine(typeof(MultiCallMethodAsyncStateMachine))] // async internal static /*async*/ Task<int> MultiCallMethodAsync_(int arg0, int arg1, int arg2, int arg3) { MultiCallMethodAsyncStateMachine multiCallMethodAsyncStateMachine = new MultiCallMethodAsyncStateMachine() { Arg0 = arg0, Arg1 = arg1, Arg2 = arg2, Arg3 = arg3, ResultToReturn = new TaskCompletionSource<int>(), // -1: Begin // 0: 1st await is done // 1: 2nd await is done // ... // -2: End State = -1 }; (multiCallMethodAsyncStateMachine as IAsyncStateMachine).MoveNext(); // Original code are in this method. return multiCallMethodAsyncStateMachine.ResultToReturn.Task; } Now the whole state machine becomes very clear - it is about callback: Original code are split into pieces by “await”s, and each piece is put into each “case” in the state machine. Here the 2 awaits split the code into 3 pieces, so there are 3 “case”s. The “piece”s are chained by callback, that is done by Builder.AwaitUnsafeOnCompleted(callback), or currentTaskToAwait.ContinueWith(callback) in the simplified code. A previous “piece” will end with a Task (which is to be awaited), when the task is done, it will callback the next “piece”. The state machine’s state works with the “case”s to ensure the code “piece”s executes one after another. Callback Since it is about callback, the simplification  can go even further – the entire state machine can be completely purged. Now MultiCallMethodAsync() becomes: internal static Task<int> MultiCallMethodAsync(int arg0, int arg1, int arg2, int arg3) { TaskCompletionSource<int> taskCompletionSource = new TaskCompletionSource<int>(); try { // Oringinal code begins. HelperMethods.Before(); MethodAsync(arg0, arg1).ContinueWith(await1 => { int resultOfAwait1 = await1.Result; HelperMethods.Continuation1(resultOfAwait1); MethodAsync(arg2, arg3).ContinueWith(await2 => { int resultOfAwait2 = await2.Result; HelperMethods.Continuation2(resultOfAwait2); int resultToReturn = resultOfAwait1 + resultOfAwait2; // Oringinal code ends. taskCompletionSource.SetResult(resultToReturn); }); }); } catch (Exception exception) { taskCompletionSource.SetException(exception); } return taskCompletionSource.Task; } Please compare with the original async / await code: HelperMethods.Before(); int resultOfAwait1 = await MethodAsync(arg0, arg1); HelperMethods.Continuation1(resultOfAwait1); int resultOfAwait2 = await MethodAsync(arg2, arg3); HelperMethods.Continuation2(resultOfAwait2); int resultToReturn = resultOfAwait1 + resultOfAwait2; return resultToReturn; Yeah that is the magic of C# async / await: Await is literally pretending to wait. In a await expression, a Task object will be return immediately so that caller is not blocked. The continuation code is compiled as that Task’s callback code. When that task is done, continuation code will execute. Please notice that many details inside the state machine are omitted for simplicity, like context caring, etc. If you want to have a detailed picture, please do check out the source code of AsyncTaskMethodBuilder and TaskAwaiter.

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  • Understanding C# async / await (1) Compilation

    - by Dixin
    Now the async / await keywords are in C#. Just like the async and ! in F#, this new C# feature provides great convenience. There are many nice documents talking about how to use async / await in specific scenarios, like using async methods in ASP.NET 4.5 and in ASP.NET MVC 4, etc. In this article we will look at the real code working behind the syntax sugar. According to MSDN: The async modifier indicates that the method, lambda expression, or anonymous method that it modifies is asynchronous. Since lambda expression / anonymous method will be compiled to normal method, we will focus on normal async method. Preparation First of all, Some helper methods need to make up. internal class HelperMethods { internal static int Method(int arg0, int arg1) { // Do some IO. WebClient client = new WebClient(); Enumerable.Repeat("http://weblogs.asp.net/dixin", 10) .Select(client.DownloadString).ToArray(); int result = arg0 + arg1; return result; } internal static Task<int> MethodTask(int arg0, int arg1) { Task<int> task = new Task<int>(() => Method(arg0, arg1)); task.Start(); // Hot task (started task) should always be returned. return task; } internal static void Before() { } internal static void Continuation1(int arg) { } internal static void Continuation2(int arg) { } } Here Method() is a long running method doing some IO. Then MethodTask() wraps it into a Task and return that Task. Nothing special here. Await something in async method Since MethodTask() returns Task, let’s try to await it: internal class AsyncMethods { internal static async Task<int> MethodAsync(int arg0, int arg1) { int result = await HelperMethods.MethodTask(arg0, arg1); return result; } } Because we used await in the method, async must be put on the method. Now we get the first async method. According to the naming convenience, it is named MethodAsync. Of course a async method can be awaited. So we have a CallMethodAsync() to call MethodAsync(): internal class AsyncMethods { internal static async Task<int> CallMethodAsync(int arg0, int arg1) { int result = await MethodAsync(arg0, arg1); return result; } } After compilation, MethodAsync() and CallMethodAsync() becomes the same logic. This is the code of MethodAsyc(): internal class CompiledAsyncMethods { [DebuggerStepThrough] [AsyncStateMachine(typeof(MethodAsyncStateMachine))] // async internal static /*async*/ Task<int> MethodAsync(int arg0, int arg1) { MethodAsyncStateMachine methodAsyncStateMachine = new MethodAsyncStateMachine() { Arg0 = arg0, Arg1 = arg1, Builder = AsyncTaskMethodBuilder<int>.Create(), State = -1 }; methodAsyncStateMachine.Builder.Start(ref methodAsyncStateMachine); return methodAsyncStateMachine.Builder.Task; } } It just creates and starts a state machine, MethodAsyncStateMachine: [CompilerGenerated] [StructLayout(LayoutKind.Auto)] internal struct MethodAsyncStateMachine : IAsyncStateMachine { public int State; public AsyncTaskMethodBuilder<int> Builder; public int Arg0; public int Arg1; public int Result; private TaskAwaiter<int> awaitor; void IAsyncStateMachine.MoveNext() { try { if (this.State != 0) { this.awaitor = HelperMethods.MethodTask(this.Arg0, this.Arg1).GetAwaiter(); if (!this.awaitor.IsCompleted) { this.State = 0; this.Builder.AwaitUnsafeOnCompleted(ref this.awaitor, ref this); return; } } else { this.State = -1; } this.Result = this.awaitor.GetResult(); } catch (Exception exception) { this.State = -2; this.Builder.SetException(exception); return; } this.State = -2; this.Builder.SetResult(this.Result); } [DebuggerHidden] void IAsyncStateMachine.SetStateMachine(IAsyncStateMachine param0) { this.Builder.SetStateMachine(param0); } } The generated code has been refactored, so it is readable and can be compiled. Several things can be observed here: The async modifier is gone, which shows, unlike other modifiers (e.g. static), there is no such IL/CLR level “async” stuff. It becomes a AsyncStateMachineAttribute. This is similar to the compilation of extension method. The generated state machine is very similar to the state machine of C# yield syntax sugar. The local variables (arg0, arg1, result) are compiled to fields of the state machine. The real code (await HelperMethods.MethodTask(arg0, arg1)) is compiled into MoveNext(): HelperMethods.MethodTask(this.Arg0, this.Arg1).GetAwaiter(). CallMethodAsync() will create and start its own state machine CallMethodAsyncStateMachine: internal class CompiledAsyncMethods { [DebuggerStepThrough] [AsyncStateMachine(typeof(CallMethodAsyncStateMachine))] // async internal static /*async*/ Task<int> CallMethodAsync(int arg0, int arg1) { CallMethodAsyncStateMachine callMethodAsyncStateMachine = new CallMethodAsyncStateMachine() { Arg0 = arg0, Arg1 = arg1, Builder = AsyncTaskMethodBuilder<int>.Create(), State = -1 }; callMethodAsyncStateMachine.Builder.Start(ref callMethodAsyncStateMachine); return callMethodAsyncStateMachine.Builder.Task; } } CallMethodAsyncStateMachine has the same logic as MethodAsyncStateMachine above. The detail of the state machine will be discussed soon. Now it is clear that: async /await is a C# language level syntax sugar. There is no difference to await a async method or a normal method. As long as a method returns Task, it is awaitable. State machine and continuation To demonstrate more details in the state machine, a more complex method is created: internal class AsyncMethods { internal static async Task<int> MultiCallMethodAsync(int arg0, int arg1, int arg2, int arg3) { HelperMethods.Before(); int resultOfAwait1 = await MethodAsync(arg0, arg1); HelperMethods.Continuation1(resultOfAwait1); int resultOfAwait2 = await MethodAsync(arg2, arg3); HelperMethods.Continuation2(resultOfAwait2); int resultToReturn = resultOfAwait1 + resultOfAwait2; return resultToReturn; } } In this method: There are multiple awaits. There are code before the awaits, and continuation code after each await After compilation, this multi-await method becomes the same as above single-await methods: internal class CompiledAsyncMethods { [DebuggerStepThrough] [AsyncStateMachine(typeof(MultiCallMethodAsyncStateMachine))] // async internal static /*async*/ Task<int> MultiCallMethodAsync(int arg0, int arg1, int arg2, int arg3) { MultiCallMethodAsyncStateMachine multiCallMethodAsyncStateMachine = new MultiCallMethodAsyncStateMachine() { Arg0 = arg0, Arg1 = arg1, Arg2 = arg2, Arg3 = arg3, Builder = AsyncTaskMethodBuilder<int>.Create(), State = -1 }; multiCallMethodAsyncStateMachine.Builder.Start(ref multiCallMethodAsyncStateMachine); return multiCallMethodAsyncStateMachine.Builder.Task; } } It creates and starts one single state machine, MultiCallMethodAsyncStateMachine: [CompilerGenerated] [StructLayout(LayoutKind.Auto)] internal struct MultiCallMethodAsyncStateMachine : IAsyncStateMachine { public int State; public AsyncTaskMethodBuilder<int> Builder; public int Arg0; public int Arg1; public int Arg2; public int Arg3; public int ResultOfAwait1; public int ResultOfAwait2; public int ResultToReturn; private TaskAwaiter<int> awaiter; void IAsyncStateMachine.MoveNext() { try { switch (this.State) { case -1: HelperMethods.Before(); this.awaiter = AsyncMethods.MethodAsync(this.Arg0, this.Arg1).GetAwaiter(); if (!this.awaiter.IsCompleted) { this.State = 0; this.Builder.AwaitUnsafeOnCompleted(ref this.awaiter, ref this); } break; case 0: this.ResultOfAwait1 = this.awaiter.GetResult(); HelperMethods.Continuation1(this.ResultOfAwait1); this.awaiter = AsyncMethods.MethodAsync(this.Arg2, this.Arg3).GetAwaiter(); if (!this.awaiter.IsCompleted) { this.State = 1; this.Builder.AwaitUnsafeOnCompleted(ref this.awaiter, ref this); } break; case 1: this.ResultOfAwait2 = this.awaiter.GetResult(); HelperMethods.Continuation2(this.ResultOfAwait2); this.ResultToReturn = this.ResultOfAwait1 + this.ResultOfAwait2; this.State = -2; this.Builder.SetResult(this.ResultToReturn); break; } } catch (Exception exception) { this.State = -2; this.Builder.SetException(exception); } } [DebuggerHidden] void IAsyncStateMachine.SetStateMachine(IAsyncStateMachine stateMachine) { this.Builder.SetStateMachine(stateMachine); } } Once again, the above state machine code is already refactored, but it still has a lot of things. More clean up can be done if we only keep the core logic, and the state machine can become very simple: [CompilerGenerated] [StructLayout(LayoutKind.Auto)] internal struct MultiCallMethodAsyncStateMachine : IAsyncStateMachine { // State: // -1: Begin // 0: 1st await is done // 1: 2nd await is done // ... // -2: End public int State; public TaskCompletionSource<int> ResultToReturn; // int resultToReturn ... public int Arg0; // int Arg0 public int Arg1; // int arg1 public int Arg2; // int arg2 public int Arg3; // int arg3 public int ResultOfAwait1; // int resultOfAwait1 ... public int ResultOfAwait2; // int resultOfAwait2 ... private Task<int> currentTaskToAwait; /// <summary> /// Moves the state machine to its next state. /// </summary> public void MoveNext() // IAsyncStateMachine member. { try { switch (this.State) { // Original code is split by "await"s into "case"s: // case -1: // HelperMethods.Before(); // MethodAsync(Arg0, arg1); // case 0: // int resultOfAwait1 = await ... // HelperMethods.Continuation1(resultOfAwait1); // MethodAsync(arg2, arg3); // case 1: // int resultOfAwait2 = await ... // HelperMethods.Continuation2(resultOfAwait2); // int resultToReturn = resultOfAwait1 + resultOfAwait2; // return resultToReturn; case -1: // -1 is begin. HelperMethods.Before(); // Code before 1st await. this.currentTaskToAwait = AsyncMethods.MethodAsync(this.Arg0, this.Arg1); // 1st task to await // When this.currentTaskToAwait is done, run this.MoveNext() and go to case 0. this.State = 0; MultiCallMethodAsyncStateMachine that1 = this; // Cannot use "this" in lambda so create a local variable. this.currentTaskToAwait.ContinueWith(_ => that1.MoveNext()); break; case 0: // Now 1st await is done. this.ResultOfAwait1 = this.currentTaskToAwait.Result; // Get 1st await's result. HelperMethods.Continuation1(this.ResultOfAwait1); // Code after 1st await and before 2nd await. this.currentTaskToAwait = AsyncMethods.MethodAsync(this.Arg2, this.Arg3); // 2nd task to await // When this.currentTaskToAwait is done, run this.MoveNext() and go to case 1. this.State = 1; MultiCallMethodAsyncStateMachine that2 = this; this.currentTaskToAwait.ContinueWith(_ => that2.MoveNext()); break; case 1: // Now 2nd await is done. this.ResultOfAwait2 = this.currentTaskToAwait.Result; // Get 2nd await's result. HelperMethods.Continuation2(this.ResultOfAwait2); // Code after 2nd await. int resultToReturn = this.ResultOfAwait1 + this.ResultOfAwait2; // Code after 2nd await. // End with resultToReturn. this.State = -2; // -2 is end. this.ResultToReturn.SetResult(resultToReturn); break; } } catch (Exception exception) { // End with exception. this.State = -2; // -2 is end. this.ResultToReturn.SetException(exception); } } /// <summary> /// Configures the state machine with a heap-allocated replica. /// </summary> /// <param name="stateMachine">The heap-allocated replica.</param> [DebuggerHidden] public void SetStateMachine(IAsyncStateMachine stateMachine) // IAsyncStateMachine member. { // No core logic. } } Only Task and TaskCompletionSource are involved in this version. And MultiCallMethodAsync() can be simplified to: [DebuggerStepThrough] [AsyncStateMachine(typeof(MultiCallMethodAsyncStateMachine))] // async internal static /*async*/ Task<int> MultiCallMethodAsync(int arg0, int arg1, int arg2, int arg3) { MultiCallMethodAsyncStateMachine multiCallMethodAsyncStateMachine = new MultiCallMethodAsyncStateMachine() { Arg0 = arg0, Arg1 = arg1, Arg2 = arg2, Arg3 = arg3, ResultToReturn = new TaskCompletionSource<int>(), // -1: Begin // 0: 1st await is done // 1: 2nd await is done // ... // -2: End State = -1 }; multiCallMethodAsyncStateMachine.MoveNext(); // Original code are moved into this method. return multiCallMethodAsyncStateMachine.ResultToReturn.Task; } Now the whole state machine becomes very clean - it is about callback: Original code are split into pieces by “await”s, and each piece is put into each “case” in the state machine. Here the 2 awaits split the code into 3 pieces, so there are 3 “case”s. The “piece”s are chained by callback, that is done by Builder.AwaitUnsafeOnCompleted(callback), or currentTaskToAwait.ContinueWith(callback) in the simplified code. A previous “piece” will end with a Task (which is to be awaited), when the task is done, it will callback the next “piece”. The state machine’s state works with the “case”s to ensure the code “piece”s executes one after another. Callback If we focus on the point of callback, the simplification  can go even further – the entire state machine can be completely purged, and we can just keep the code inside MoveNext(). Now MultiCallMethodAsync() becomes: internal static Task<int> MultiCallMethodAsync(int arg0, int arg1, int arg2, int arg3) { TaskCompletionSource<int> taskCompletionSource = new TaskCompletionSource<int>(); try { // Oringinal code begins. HelperMethods.Before(); MethodAsync(arg0, arg1).ContinueWith(await1 => { int resultOfAwait1 = await1.Result; HelperMethods.Continuation1(resultOfAwait1); MethodAsync(arg2, arg3).ContinueWith(await2 => { int resultOfAwait2 = await2.Result; HelperMethods.Continuation2(resultOfAwait2); int resultToReturn = resultOfAwait1 + resultOfAwait2; // Oringinal code ends. taskCompletionSource.SetResult(resultToReturn); }); }); } catch (Exception exception) { taskCompletionSource.SetException(exception); } return taskCompletionSource.Task; } Please compare with the original async / await code: HelperMethods.Before(); int resultOfAwait1 = await MethodAsync(arg0, arg1); HelperMethods.Continuation1(resultOfAwait1); int resultOfAwait2 = await MethodAsync(arg2, arg3); HelperMethods.Continuation2(resultOfAwait2); int resultToReturn = resultOfAwait1 + resultOfAwait2; return resultToReturn; Yeah that is the magic of C# async / await: Await is not to wait. In a await expression, a Task object will be return immediately so that execution is not blocked. The continuation code is compiled as that Task’s callback code. When that task is done, continuation code will execute. Please notice that many details inside the state machine are omitted for simplicity, like context caring, etc. If you want to have a detailed picture, please do check out the source code of AsyncTaskMethodBuilder and TaskAwaiter.

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  • sybase bcp import fails

    - by chromeplatedbanana
    We're trying to export some tables from our production database to our test database using bcp. The bcp export seems to work fine, but the import always fails with a data type error (see below). We tested on our test database exporting the table content to a file, then importing it in again immediately, but that failed too. e.g., bcp TABLENAME out ~/tempfile -S servername -U username generates a file as expected. If we use -c option then the number of lines is as expected. However, bcp TABLENAME in ~/tempfile -S servername -U username fails with CTLIB Message: - L0/0D/S0/N0/0/0: blk_int(): blk_layer: CT library error: Cannot find an equivalent CS_TYPE for this TDS data type 49 blk_init failed. We get this whenever we try to copy into TABLENAME, whether from the production or test table dump file. I don't understand why export and import for the same TABLENAME is generating a data type error. What am I doing wrong here? Thanks

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  • Need HP recovery partition info

    - by ggambett
    I'm configuring a new HP Pavillion DV4 with a 320 GB disk. I made the recovery DVDs, then did a couple other things (including deleting the recovery partition), and finally decided to restore the system. Unfortunately, the recovery process fails; the three DVDs are read (the recovery program says "Reformatting the Windows partition" and "Copying files required to restore the hard drive") but after it finishes reading the 3rd, and the progress bar reaches 100%, it fails with error 0xe0f00013 - Googling it didn't return anything at all. I'm afraid this may be because I deleted the partitions. So, I'm kindly asking for one of the following, in order of preference, from a HP Pavillion DV4 with a 320 GB hard disk or a similar enough one : 1) A dump of the MBR 2) The type and size of all the partitions in a "new" system so I can try to make a partition table resembling the original one. BTW, I thought the recovery DVDs were supposed to work even if the entire disk was wiped - isn't that the case? Thanks!

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  • VMWare workstation: from command line, how to start a VM in service mode (run in background)?

    - by GenEric35
    Hi, I have tried the vmrun and vmware.exe executables, but both of them start the vmware GUI when starting the VM. What I want to do is start the VM without starting the VMWare GUI. The reason I am doing this is after a few hours of idle, the guest OS becomes sluggish. It has lots of RAM but the only way I found to keep it's responsiveness optimal is to shutdown(dumps the memory) and the start; a restart of the guest OS doesnt dump the memory so I need to be able to do a stop of the VM, and then a start. So far the command I use are: C:\Program Files (x86)\VMware\VMware Workstationvmrun stop F:\VirtualMachines\R2\R2.vmx C:\Program Files (x86)\VMware\VMware Workstationvmrun start F:\VirtualMachines\R2\R2.vmx But the start command actually starts the VMWare Workstation GUI, which I don't need. I'm looking for a solution to start the VM without the VMWare Wokstation GUI, or a solution to what is causing the VM to become sluggish after a few hours of running idle.

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  • PSExec on Windows 2008 R2 Failing "Network name cannot be found"

    - by Adam Frisby
    Hi, We've got a bunch of remote admin scripts which rely on psexec and they do not appear to be working over the network on our new 2008 hosts. An error dump is below: C:\Users\<user>\Desktop\PsTools> psexec \\<host IP> -u Administrator -p <pass> <cmd> PsExec v1.97 - Execute processes remotely Copyright (C) 2001-2009 Mark Russinovich Sysinternals - www.sysinternals.com Couldn't access <host IP>: The network name cannot be found. Make sure that the default admin$ share is enabled on <host IP>. We've tried both the machine name and the IP address in with the same results. The same command has worked previously with our Win2K3 hosts - so we're presuming it is some form of security change between the 2003 and 2008R2. Anyone have any clues?

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