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  • Java Non-Blocking HTTP Server

    - by Marcus
    I have written an application using embedded Jetty that makes network calls to other services. I presume that the serving threads are idle whilst waiting for the network calls to complete. Is there any way to have a worker thread that switches between requests to perform work that can be done at the current time and then when the network calls return also handle that? A request would be returned when all work has been completed for it. I know this is a common paradigm, and I have used it for non-blocking TCP networking, but I'm unsure as to how to achieve this on a Java HTTP server whilst also waiting on external results. Any links or explanations are appreciated. Thanks

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  • My C# program running as Windows Service is blocking Windows XP from hibernation

    - by sherpa
    I have Windows Service written in C#. It starts two threads, one is pooling a Web Service, second is waiting on a Monitor object for a new job to arrive. Besides that, the main thread acts as a WCF service host using NetNamedPipeBinding. It lets the client application to register a callback and then sends notifications back. The problem I have is that when this Windows Service is running, I cannot hibernate or Standby my computer which is running on Windows XP, SP3. When I set Windows to hibernate or standby, nothing happens. Then, at the moment when I go to Service Manager and stop the service, the system hibernation starts immediately. The service class extending the ServiceBase has properties like CanHandlePowerEvent, CanPauseAndContinue, etc. set to true... That didn't make any difference. The question is: what can be blocking the Hibernation/Standby from proceeding? What should I take care about to avoid it?

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  • Java blocking socket returning incomplete ByteBuffer

    - by evandro-carrenho
    I have a socketChannel configured as blocking, but when reading byte buffers of 5K from this socket, I get an incomplete buffer sometimes. ByteBuffer messageBody = ByteBuffer.allocate(5*1024); messageBody.mark(); messageBody.order(ByteOrder.BIG_ENDIAN); int msgByteCount = channel.read(messageBody); Ocasionally, messageBody is not completely filled and channel.read() does not return -1 or an exception, but the actual number of bytes read (which is less than 5k). Has anyone experienced a similar problem?

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  • Force blocking read after EAGAIN?

    - by Daniel Trebbien
    I have a file descriptor that is open for reading which may be non-blocking. What I need to do is simply read all data until reaching EOF and write that data to a writable file descriptor. As the process that performs this copying is not "aware" of anything that is going on around it, I don't think that I can do something useful while waiting for data, and I don't want to use a while loop (while errno is not EAGAIN) because I think that it would be wasteful. Is there a way to block or otherwise suspend execution of the copying process until data becomes available?

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  • Sleeping a thread blocking stdin

    - by Sid
    Hey, I'm running a function which evaluates commands passed in using stdin and another function which runs a bunch of jobs. I need to make the latter function sleep at regular intervals but that seems to be blocking the stdin. Any advice on how to resolve this would be appreciated. The source code for the functions is def runJobs(comps, jobQueue, numRunning, limit, lock): while len(jobQueue) >= 0: print(len(jobQueue)); if len(jobQueue) > 0: comp, tasks = find_computer(comps, 0); #do something time.sleep(5); def manageStdin(): print "Global Stdin Begins Now" for line in fileinput.input(): try: print(eval(line)); except Exception, e: print e; --Thanks

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  • Can single-buffer blocking WSASend deliver partial data?

    - by CodeAngry
    I've pretty much always used send() with sockets and now I'm moving onto the WSA functions. With send(), I have a sendall() helper that ensured all data is delivered even if it didn't happen in one try and a partial send occurred on first call. So, instead of learning the hard way or over-complicating code when I don't have to, decided to ask you: Can a blocking WSASend() send partial data or does it send everything before it returns or fails? Or should I check the bytes sent vs. expected to send and keep at it until everything is delivered? ANSWER: Overlapped WSASend() does not send partial data but if it does, it means the connection has terminated. I've never encountered the case yet.

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  • Algorithm for querying linearly through a non-linear list of questions

    - by JoshLeaves
    For a multiplayers trivia game, I need to supply my users with a new quizz in a desired subject (Science, Maths, Litt. and such) at the start of every game. I've generated about 5K quizzes for each subject and filled my database with them. So my 'Quizzes' database looks like this: |ID |Subject |Question +-----+------------+---------------------------------- | 23 |Science | What's water? | 42 |Maths | What's 2+2? | 99 |Litt. | Who wrote "Pride and Prejudice"? | 123 |Litt. | Who wrote "On The Road"? | 146 |Maths | What's 2*2? | 599 |Science | You know what's cool? |1042 |Maths | What's the Fibonacci Sequence? |1056 |Maths | What's 42? And so on... (Much more detailed/complex but I'll keep the exemple simple) As you can see, due to technical constraints (MongoDB), my IDs are not linear but I can use them as an increasing suite. So far, my algorithm to ensure two users get a new quizz when they play together is the following: // Take the last played quizzes by P1 and P2 var q_one = player_one.getLastPlayedQuizz('Maths'); var q_two = player_two.getLastPlayedQuizz('Maths'); // If both of them never played in the subject, return first quizz in the list if ((q_one == NULL) && (q_two == NULL)) return QuizzDB.findOne({subject: 'Maths'}); // If one of them never played, play the next quizz for the other player // This quizz is found by asking for the first quizz in the desired subject where // the ID is greater than the last played quizz's ID (if the last played quizz ID // is 42, this will return 146 following the above example database) if (q_one == NULL) return QuizzDB.findOne({subject: 'Maths', ID > q_two}); if (q_two == NULL) return QuizzDB.findOne({subject: 'Maths', ID > q_one}); // And if both of them have a lastPlayedQuizz, we return the next quizz for the // player whose lastPlayedQuizz got the higher ID if (q_one > q_two) return QuizzDB.findOne({subject: 'Maths', ID > q_one}); else return QuizzDB.findOne({subject: 'Maths', ID > q_two}); Now here comes the real problem: Once I get to the end of my database (let's say, P1's last played quizz in 'Maths' is 1056, P2's is 146 and P3 is 1042), following my algorithm, P1's ID is the highest so I ask for the next question in 'Maths' where ID is superior to 1056. There is nothing, so I roll back to the beginning of my quizz list (with a random skipper to avoid having the first question always show up). P1 and P2's last played will then be 42 and they will start fresh from the beginning of the list. However, if P1 (42) plays against P3 (1042), the resulting ID will be 1056...which P1 already played two games ago. Basically, players who just "rolled back" to the beginning of the list will be brought back to the end of the list by players who still haven't rolled back. The rollback WILL happen in the end, but it'll take time and there'll be a "bottleneck" at the beginning and at the end. Thus my question: What would be the best algorith to avoid this bottleneck and ensure players don't get stuck endlessly on the same quizzes? Also bear in mind that I've got some technical constraints: I can't get a random question in a subject (ie: no "QuizzDB.findOne({subject: 'Maths'}).skip(random());"). It's cool to skip on one to twenty records, but the MongoDB documentation warns against skipping too many documents. I would like to avoid building an array of every quizz played by each player and find the next non-played in the database with a $nin. Thanks for your help

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  • How to resize / enlarge / grow a non-LVM ext4 partition

    - by Mischa
    I have already searched the forums, but couldnt find a good suitable answer: I have an Ubuntu Server 10.04 as KVM Host and a guest system, that also runs 10.04. The host system uses LVM and there are three logical volumes, which are provided to the guest as virtual block devices - one for /, one for /home and one for swap. The guest had been partitioned without LVM. I have already enlarged the logical volume in the host system - the guest successfully sees the bigger virtual disk. However, this virtual disk contains one "good old" partition, which still has the old small size. The output of fdisk -l is me@produktion:/$ LC_ALL=en_US sudo fdisk -l Disk /dev/vda: 32.2 GB, 32212254720 bytes 255 heads, 63 sectors/track, 3916 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk identifier: 0x000c8ce7 Device Boot Start End Blocks Id System /dev/vda1 * 1 3917 31455232 83 Linux Disk /dev/vdb: 2147 MB, 2147483648 bytes 244 heads, 47 sectors/track, 365 cylinders Units = cylinders of 11468 * 512 = 5871616 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk identifier: 0x000f2bf7 Device Boot Start End Blocks Id System /dev/vdb1 1 366 2095104 82 Linux swap / Solaris Partition 1 has different physical/logical beginnings (non-Linux?): phys=(0, 32, 33) logical=(0, 43, 28) Partition 1 has different physical/logical endings: phys=(260, 243, 47) logical=(365, 136, 44) Disk /dev/vdc: 225.5 GB, 225485783040 bytes 255 heads, 63 sectors/track, 27413 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk identifier: 0x00027f25 Device Boot Start End Blocks Id System /dev/vdc1 1 9138 73398272 83 Linux The output of parted print all is Model: Virtio Block Device (virtblk) Disk /dev/vda: 32.2GB Sector size (logical/physical): 512B/512B Partition Table: msdos Number Start End Size Type File system Flags 1 1049kB 32.2GB 32.2GB primary ext4 boot Model: Virtio Block Device (virtblk) Disk /dev/vdb: 2147MB Sector size (logical/physical): 512B/512B Partition Table: msdos Number Start End Size Type File system Flags 1 1049kB 2146MB 2145MB primary linux-swap(v1) Model: Virtio Block Device (virtblk) Disk /dev/vdc: 225GB Sector size (logical/physical): 512B/512B Partition Table: msdos Number Start End Size Type File system Flags 1 1049kB 75.2GB 75.2GB primary ext4 What I want to achieve is to simply grow or resize the partition /dev/vdc1 so that it uses the whole space provided by the virtual block device /dev/vdc. The problem is, that when I try to do that with parted, it complains: (parted) select /dev/vdc Using /dev/vdc (parted) print Model: Virtio Block Device (virtblk) Disk /dev/vdc: 225GB Sector size (logical/physical): 512B/512B Partition Table: msdos Number Start End Size Type File system Flags 1 1049kB 75.2GB 75.2GB primary ext4 (parted) resize 1 WARNING: you are attempting to use parted to operate on (resize) a file system. parted's file system manipulation code is not as robust as what you'll find in dedicated, file-system-specific packages like e2fsprogs. We recommend you use parted only to manipulate partition tables, whenever possible. Support for performing most operations on most types of file systems will be removed in an upcoming release. Start? [1049kB]? End? [75.2GB]? 224GB Error: File system has an incompatible feature enabled. Compatible features are has_journal, dir_index, filetype, sparse_super and large_file. Use tune2fs or debugfs to remove features. So what can I do? This is a headless production system. What is a safe way to grow this partition? I CAN unmount it, though - so this is not the problem.

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  • OBI10g will be Non-Qualifying for OPN Specialisation in September 2013

    - by Mike.Hallett(at)Oracle-BI&EPM
    aboteste 12.00 Just to alert you, that OPN Specialisation is software version-specific: so as we bring out new product versions, so the specialisation crtiteria and exam needs to keep updated to the new version. Specifically for our analytics partners, be aware that your “OBI10g Specialisation” credentials will be Non-Qualifying for OPN Specialisation in September 2013. Therefore to keep your profile up to date please start now to take the latest OBI11g exams and apply to OPN to upgrade to “OBI11g Specialisation”. Find out more about the new version OBI11g Exams to update your OPN Specialisation @ OPN Exam for OBI Suite 11g is Now LIVE, and more generally the Update on BI & EPM Specializations and Knowledge Zones. aboteste 12.00 Normal 0 false false false EN-GB X-NONE X-NONE MicrosoftInternetExplorer4 /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-qformat:yes; mso-style-parent:""; mso-padding-alt:0cm 5.4pt 0cm 5.4pt; mso-para-margin-top:0cm; mso-para-margin-right:0cm; mso-para-margin-bottom:10.0pt; mso-para-margin-left:0cm; line-height:115%; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:"Times New Roman"; mso-bidi-theme-font:minor-bidi; mso-fareast-language:EN-US;} And to help you pass, see the Oracle Business Intelligence Foundation Suite 11 Essentials Exam Study Guide. Also check the documents on OPN for Frequently Asked Questions for Product Version Specialization and the latest Specializations Catalog. Normal 0 false false false EN-GB X-NONE X-NONE MicrosoftInternetExplorer4 /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-qformat:yes; mso-style-parent:""; mso-padding-alt:0cm 5.4pt 0cm 5.4pt; mso-para-margin-top:0cm; mso-para-margin-right:0cm; mso-para-margin-bottom:10.0pt; mso-para-margin-left:0cm; line-height:115%; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:"Times New Roman"; mso-bidi-theme-font:minor-bidi; mso-fareast-language:EN-US;}

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  • Determine duplicate record for duplicate and non-duplicate records

    - by gibboo
    I have a files containing both duplicate and non-duplicate records. The file is already sorted by a key. I want to determine those records that are duplicate and records that are non-duplicate. If duplicate the record is moved to a duplicate file and if non-duplicate that will be moved to valid file. I am using COBOL, and occurence of records for duplicate and non-duplicate is more than twice.

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  • Is Gmail Being Blocked by my ISP?

    - by james
    I asked this over at superuser but they weren't able to help, so I was hoping the sysadmins here will be able to advise as to what's wrong. Although the issue here is with a PC and not a server it still deals with networking so I hope it's not too irrelevant. The Issue: I have a desktop on which I cannot access Gmail and also youtube sign in (I believe since youtube is owned by google they both use the same sign in system). On other computers that uses the same connection via a wireless router I can access both gmail and youtube sign in just fine. On this computer which doesn't have a wireless card and so I have to connect via Ethernet cable (connected to a USB converter since the Ethernet port doesn't work anymore) I can access all sites and services including things like aol and hotmail. But only when it comes to gmail, do I get complete and utter throttling. I even turned off my AV ad Firewall momentarily and no luck. The gmail log in page starts to load and by mid point it just stays there loading and loading and loading... never ends. I tried everything, I reset the modem and router multiple times. I reinstalled my operating system from a vista to a windows 7 hoping that a complete reinstall would solve the issue, but no luck. And yes, I am going to call my ISP but not to solve this issue, but to cancel them. I want to upgrade to cable from DSL anyway. I didn't mention my ISP because I'm not sure if that is within the rules (if it's okay some one let me know and I will). P.S. All this happened one day, before that gmail was perfectly accessible in this computer. I can't remember anything special happening on that day prior to this. The only thing I can think of is, my ISP or Google itself is blocking this computer based on it's mac address, but I don't know if that's even done. Additional info: PC: Windows 7 Ultimate 32 bit Connection Type: DSL Connecting Medium: Ethernet cable via USB converter EDIT: I should mention I can access gmail and youtube just fine through a IP proxy service.

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  • Is Gmail Being Blocked by my ISP?

    - by james
    EDIT: I thought I pinpointed the problem. Just now I tried to go to the firefox addons page which uses https and gmail also uses https. So I thought I am unable to load https pages on this computer. So I went to a bank site which uses https but that loads just fine. Sigh.... I asked this over at superuser but they weren't able to help, so I was hoping the sysadmins here will be able to advise as to what's wrong. Although the issue here is with a PC and not a server it still deals with networking so I hope it's not too irrelevant. The Issue: I have a desktop on which I cannot access Gmail and also youtube sign in (I believe since youtube is owned by google they both use the same sign in system). On other computers that uses the same connection via a wireless router I can access both gmail and youtube sign in just fine. On this computer which doesn't have a wireless card and so I have to connect via Ethernet cable (connected to a USB converter since the Ethernet port doesn't work anymore) I can access all sites and services including things like aol and hotmail. But only when it comes to gmail, do I get complete and utter throttling. I even turned off my AV ad Firewall momentarily and no luck. The gmail log in page starts to load and by mid point it just stays there loading and loading and loading... never ends. I tried everything, I reset the modem and router multiple times. I reinstalled my operating system from a vista to a windows 7 hoping that a complete reinstall would solve the issue, but no luck. And yes, I am going to call my ISP but not to solve this issue, but to cancel them. I want to upgrade to cable from DSL anyway. I didn't mention my ISP because I'm not sure if that is within the rules (if it's okay some one let me know and I will). P.S. All this happened one day, before that gmail was perfectly accessible in this computer. I can't remember anything special happening on that day prior to this. The only thing I can think of is, my ISP or Google itself is blocking this computer based on it's mac address, but I don't know if that's even done. Additional info: PC: Windows 7 Ultimate 32 bit Connection Type: DSL Connecting Medium: Ethernet cable via USB converter I should mention I can access gmail and youtube just fine through a IP proxy service.

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  • Apache VirtualHost Blockhole (Eats All Requests on All Ports on an IP)

    - by Synetech inc.
    I’m exhausted. I just spent the last two hours chasing a goose that I have been after on-and-off for the past year. Here is the goal, put as succinctly as possible. Step 1: HOSTS File: 127.0.0.5 NastyAdServer.com 127.0.0.5 xssServer.com 127.0.0.5 SQLInjector.com 127.0.0.5 PornAds.com 127.0.0.5 OtherBadSites.com … Step 2: Apache httpd.conf <VirtualHost 127.0.0.5:80> ServerName adkiller DocumentRoot adkiller RewriteEngine On RewriteRule (\.(gif|jpg|png|jpeg)$) /p.png [L] RewriteRule (.*) /ad.htm [L] </VirtualHost> So basically what happens is that the HOSTS file redirects designated domains to the localhost, but to a specific loopback IP address. Apache listens for any requests on this address and serves either a transparent pixel graphic, or else an empty HTML file. Thus, any page or graphic on any of the bad sites is replaced with nothing (in other words an ad/malware/porn/etc. blocker). This works great as is (and has been for me for years now). The problem is that these bad things are no longer limited to just HTTP traffic. For example: <script src="http://NastyAdServer.com:99"> or <iframe src="https://PornAds.com/ad.html"> or a Trojan using ftp://spammaster.com/[email protected];[email protected];[email protected] or an app “phoning home” with private info in a crafted ICMP packet by pinging CardStealer.ru:99 Handling HTTPS is a relatively minor bump. I can create a separate VirtualHost just like the one above, replacing port 80 with 443, and adding in SSL directives. This leaves the other ports to be dealt with. I tried using * for the port, but then I get overlap errors. I tried redirecting all request to the HTTPS server and visa-versa but neither worked; either the SSL requests wouldn’t redirect correctly or else the HTTP requests gave the You’re speaking plain HTTP to an SSL-enabled server port… error. Further, I cannot figure out a way to test if other ports are being successfully redirected (I could try using a browser, but what about FTP, ICMP, etc.?) I realize that I could just use a port-blocker (eg ProtoWall, PeerBlock, etc.), but there’s two issues with that. First, I am blocking domains with this method, not IP addresses, so to use a port-blocker, I would have to get each and every domain’s IP, and update theme frequently. Second, using this method, I can have Apache keep logs of all the ad/malware/spam/etc. requests for future analysis (my current AdKiller logs are already 466MB right now). I appreciate any help in successfully setting up an Apache VirtualHost blackhole. Thanks.

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  • Technical non-terminating condition in a loop

    - by Snarfblam
    Most of us know that a loop should not have a non-terminating condition. For example, this C# loop has a non-terminating condition: any even value of i. This is an obvious logic error. void CountByTwosStartingAt(byte i) { // If i is even, it never exceeds 254 for(; i < 255; i += 2) { Console.WriteLine(i); } } Sometimes there are edge cases that are extremely unlikeley, but technically constitute non-exiting conditions (stack overflows and out-of-memory errors aside). Suppose you have a function that counts the number of sequential zeros in a stream: int CountZeros(Stream s) { int total = 0; while(s.ReadByte() == 0) total++; return total; } Now, suppose you feed it this thing: class InfiniteEmptyStream:Stream { // ... Other members ... public override int Read(byte[] buffer, int offset, int count) { Array.Clear(buffer, offset, count); // Output zeros return count; // Never returns -1 (end of stream) } } Or more realistically, maybe a stream that returns data from external hardware, which in certain cases might return lots of zeros (such as a game controller sitting on your desk). Either way we have an infinite loop. This particular non-terminating condition stands out, but sometimes they don't. A completely real-world example as in an app I'm writing. An endless stream of zeros will be deserialized into infinite "empty" objects (until the collection class or GC throws an exception because I've exceeded two billion items). But this would be a completely unexpected circumstance (considering my data source). How important is it to have absolutely no non-terminating conditions? How much does this affect "robustness?" Does it matter if they are only "theoretically" non-terminating (is it okay if an exception represents an implicit terminating condition)? Does it matter whether the app is commercial? If it is publicly distributed? Does it matter if the problematic code is in no way accessible through a public interface/API? Edit: One of the primary concerns I have is unforseen logic errors that can create the non-terminating condition. If, as a rule, you ensure there are no non-terminating conditions, you can identify or handle these logic errors more gracefully, but is it worth it? And when? This is a concern orthogonal to trust.

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  • Non-Dom Element Event Binding with jQuery

    - by Rick Strahl
    Yesterday I had a short discussion with Dave Reed on Twitter regarding setting up fake ‘events’ on objects that are hookable. jQuery makes it real easy to bind events on DOM elements and with a little bit of extra work (that I didn’t know about) you can also set up binding to non-DOM element ‘event’ bindings. Assume for a second that you have a simple JavaScript object like this: var item = { sku: "wwhelp" , foo: function() { alert('orginal foo function'); } }; and you want to be notified when the foo function is called. You can use jQuery to bind the handler like this: $(item).bind("foo", function () { alert('foo Hook called'); } ); Binding alone won’t actually cause the handler to be triggered so when you call: item.foo(); you only get the ‘original’ message. In order to fire both the original handler and the bound event hook you have to use the .trigger() function: $(item).trigger("foo"); Now if you do the following complete sequence: var item = { sku: "wwhelp" , foo: function() { alert('orginal foo function'); } }; $(item).bind("foo", function () { alert('foo hook called'); } ); $(item).trigger("foo"); You’ll see the ‘hook’ message first followed by the ‘original’ message fired in succession. In other words, using this mechanism you can hook standard object functions and chain events to them in a way similar to the way you can do with DOM elements. The main difference is that the ‘event’ has to be explicitly triggered in order for this to happen rather than just calling the method directly. .trigger() relies on some internal logic that checks for event bindings on the object (attached via an expando property) which .trigger() searches for in its bound event list. Once the ‘event’ is found it’s called prior to execution of the original function. This is pretty useful as it allows you to create standard JavaScript objects that can act as event handlers and are effectively hookable without having to explicitly override event definitions with JavaScript function handlers. You get all the benefits of jQuery’s event methods including the ability to hook up multiple events to the same handler function and the ability to uniquely identify each specific event instance with post fix string names (ie. .bind("MyEvent.MyName") and .unbind("MyEvent.MyName") to bind MyEvent). Watch out for an .unbind() Bug Note that there appears to be a bug with .unbind() in jQuery that doesn’t reliably unbind an event and results in a elem.removeEventListener is not a function error. The following code demonstrates: var item = { sku: "wwhelp", foo: function () { alert('orginal foo function'); } }; $(item).bind("foo.first", function () { alert('foo hook called'); }); $(item).bind("foo.second", function () { alert('foo hook2 called'); }); $(item).trigger("foo"); setTimeout(function () { $(item).unbind("foo"); // $(item).unbind("foo.first"); // $(item).unbind("foo.second"); $(item).trigger("foo"); }, 3000); The setTimeout call delays the unbinding and is supposed to remove the event binding on the foo function. It fails both with the foo only value (both if assigned only as “foo” or “foo.first/second” as well as when removing both of the postfixed event handlers explicitly. Oddly the following that removes only one of the two handlers works: setTimeout(function () { //$(item).unbind("foo"); $(item).unbind("foo.first"); // $(item).unbind("foo.second"); $(item).trigger("foo"); }, 3000); this actually works which is weird as the code in unbind tries to unbind using a DOM method that doesn’t exist. <shrug> A partial workaround for unbinding all ‘foo’ events is the following: setTimeout(function () { $.event.special.foo = { teardown: function () { alert('teardown'); return true; } }; $(item).unbind("foo"); $(item).trigger("foo"); }, 3000); which is a bit cryptic to say the least but it seems to work more reliably. I can’t take credit for any of this – thanks to Dave Reed and Damien Edwards who pointed out some of these behaviors. I didn’t find any good descriptions of the process so thought it’d be good to write it down here. Hope some of you find this helpful.© Rick Strahl, West Wind Technologies, 2005-2010Posted in jQuery  

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  • Some non-generic collections

    - by Simon Cooper
    Although the collections classes introduced in .NET 2, 3.5 and 4 cover most scenarios, there are still some .NET 1 collections that don't have generic counterparts. In this post, I'll be examining what they do, why you might use them, and some things you'll need to bear in mind when doing so. BitArray System.Collections.BitArray is conceptually the same as a List<bool>, but whereas List<bool> stores each boolean in a single byte (as that's what the backing bool[] does), BitArray uses a single bit to store each value, and uses various bitmasks to access each bit individually. This means that BitArray is eight times smaller than a List<bool>. Furthermore, BitArray has some useful functions for bitmasks, like And, Xor and Not, and it's not limited to 32 or 64 bits; a BitArray can hold as many bits as you need. However, it's not all roses and kittens. There are some fundamental limitations you have to bear in mind when using BitArray: It's a non-generic collection. The enumerator returns object (a boxed boolean), rather than an unboxed bool. This means that if you do this: foreach (bool b in bitArray) { ... } Every single boolean value will be boxed, then unboxed. And if you do this: foreach (var b in bitArray) { ... } you'll have to manually unbox b on every iteration, as it'll come out of the enumerator an object. Instead, you should manually iterate over the collection using a for loop: for (int i=0; i<bitArray.Length; i++) { bool b = bitArray[i]; ... } Following on from that, if you want to use BitArray in the context of an IEnumerable<bool>, ICollection<bool> or IList<bool>, you'll need to write a wrapper class, or use the Enumerable.Cast<bool> extension method (although Cast would box and unbox every value you get out of it). There is no Add or Remove method. You specify the number of bits you need in the constructor, and that's what you get. You can change the length yourself using the Length property setter though. It doesn't implement IList. Although not really important if you're writing a generic wrapper around it, it is something to bear in mind if you're using it with pre-generic code. However, if you use BitArray carefully, it can provide significant gains over a List<bool> for functionality and efficiency of space. OrderedDictionary System.Collections.Specialized.OrderedDictionary does exactly what you would expect - it's an IDictionary that maintains items in the order they are added. It does this by storing key/value pairs in a Hashtable (to get O(1) key lookup) and an ArrayList (to maintain the order). You can access values by key or index, and insert or remove items at a particular index. The enumerator returns items in index order. However, the Keys and Values properties return ICollection, not IList, as you might expect; CopyTo doesn't maintain the same ordering, as it copies from the backing Hashtable, not ArrayList; and any operations that insert or remove items from the middle of the collection are O(n), just like a normal list. In short; don't use this class. If you need some sort of ordered dictionary, it would be better to write your own generic dictionary combining a Dictionary<TKey, TValue> and List<KeyValuePair<TKey, TValue>> or List<TKey> for your specific situation. ListDictionary and HybridDictionary To look at why you might want to use ListDictionary or HybridDictionary, we need to examine the performance of these dictionaries compared to Hashtable and Dictionary<object, object>. For this test, I added n items to each collection, then randomly accessed n/2 items: So, what's going on here? Well, ListDictionary is implemented as a linked list of key/value pairs; all operations on the dictionary require an O(n) search through the list. However, for small n, the constant factor that big-o notation doesn't measure is much lower than the hashing overhead of Hashtable or Dictionary. HybridDictionary combines a Hashtable and ListDictionary; for small n, it uses a backing ListDictionary, but switches to a Hashtable when it gets to 9 items (you can see the point it switches from a ListDictionary to Hashtable in the graph). Apart from that, it's got very similar performance to Hashtable. So why would you want to use either of these? In short, you wouldn't. Any gain in performance by using ListDictionary over Dictionary<TKey, TValue> would be offset by the generic dictionary not having to cast or box the items you store, something the graphs above don't measure. Only if the performance of the dictionary is vital, the dictionary will hold less than 30 items, and you don't need type safety, would you use ListDictionary over the generic Dictionary. And even then, there's probably more useful performance gains you can make elsewhere.

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  • IntelliSense for Razor Hosting in non-Web Applications

    - by Rick Strahl
    When I posted my Razor Hosting article a couple of weeks ago I got a number of questions on how to get IntelliSense to work inside of Visual Studio while editing your templates. The answer to this question is mainly dependent on how Visual Studio recognizes assemblies, so a little background is required. If you open a template just on its own as a standalone file by clicking on it say in Explorer, Visual Studio will open up with the template in the editor, but you won’t get any IntelliSense on any of your related assemblies that you might be using by default. It’ll give Intellisense on base System namespace, but not on your imported assembly types. This makes sense: Visual Studio has no idea what the assembly associations for the single file are. There are two options available to you to make IntelliSense work for templates: Add the templates as included files to your non-Web project Add a BIN folder to your template’s folder and add all assemblies required there Including Templates in your Host Project By including templates into your Razor hosting project, Visual Studio will pick up the project’s assembly references and make IntelliSense available for any of the custom types in your project and on your templates. To see this work I moved the \Templates folder from the samples from the Debug\Bin folder into the project root and included the templates in the WinForm sample project. Here’s what this looks like in Visual Studio after the templates have been included:   Notice that I take my original example and type cast the Context object to the specific type that it actually represents – namely CustomContext – by using a simple code block: @{ CustomContext Model = Context as CustomContext; } After that assignment my Model local variable is in scope and IntelliSense works as expected. Note that you also will need to add any namespaces with the using command in this case: @using RazorHostingWinForm which has to be defined at the very top of a Razor document. BTW, while you can only pass in a single Context 'parameter’ to the template with the default template I’ve provided realize that you can also assign a complex object to Context. For example you could have a container object that references a variety of other objects which you can then cast to the appropriate types as needed: @{ ContextContainer container = Context as ContextContainer; CustomContext Model = container.Model; CustomDAO DAO = container.DAO; } and so forth. IntelliSense for your Custom Template Notice also that you can get IntelliSense for the top level template by specifying an inherits tag at the top of the document: @inherits RazorHosting.RazorTemplateFolderHost By specifying the above you can then get IntelliSense on your base template’s properties. For example, in my base template there are Request and Response objects. This is very useful especially if you end up creating custom templates that include your custom business objects as you can get effectively see full IntelliSense from the ‘page’ level down. For Html Help Builder for example, I’d have a Help object on the page and assuming I have the references available I can see all the way into that Help object without even having to do anything fancy. Note that the @inherits key is a GREAT and easy way to override the base template you normally specify as the default template. It allows you to create a custom template and as long as it inherits from the base template it’ll work properly. Since the last post I’ve also made some changes in the base template that allow hooking up some simple initialization logic so it gets much more easy to create custom templates and hook up custom objects with an IntializeTemplate() hook function that gets called with the Context and a Configuration object. These objects are objects you can pass in at runtime from your host application and then assign to custom properties on your template. For example the default implementation for RazorTemplateFolderHost does this: public override void InitializeTemplate(object context, object configurationData) { // Pick up configuration data and stuff into Request object RazorFolderHostTemplateConfiguration config = configurationData as RazorFolderHostTemplateConfiguration; this.Request.TemplatePath = config.TemplatePath; this.Request.TemplateRelativePath = config.TemplateRelativePath; // Just use the entire ConfigData as the model, but in theory // configData could contain many objects or values to set on // template properties this.Model = config.ConfigData as TModel; } to set up a strongly typed Model and the Request object. You can do much more complex hookups here of course and create complex base template pages that contain all the objects that you need in your code with strong typing. Adding a Bin folder to your Template’s Root Path Including templates in your host project works if you own the project and you’re the only one modifying the templates. However, if you are distributing the Razor engine as a templating/scripting solution as part of your application or development tool the original project is likely not available and so that approach is not practical. Another option you have is to add a Bin folder and add all the related assemblies into it. You can also add a Web.Config file with assembly references for any GAC’d assembly references that need to be associated with the templates. Between the web.config and bin folder Visual Studio can figure out how to provide IntelliSense. The Bin folder should contain: The RazorHosting.dll Your host project’s EXE or DLL – renamed to .dll if it’s an .exe Any external (bin folder) dependent assemblies Note that you most likely also want a reference to the host project if it contains references that are going to be used in templates. Visual Studio doesn’t recognize an EXE reference so you have to rename the EXE to DLL to make it work. Apparently the binary signature of EXE and DLL files are identical and it just works – learn something new everyday… For GAC assembly references you can add a web.config file to your template root. The Web.config file then should contain any full assembly references to GAC components: <configuration> <system.web> <compilation debug="true"> <assemblies> <add assembly="System.Web.Mvc, Version=3.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" /> <add assembly="System.Web, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" /> <add assembly="System.Web.Extensions, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" /> </assemblies> </compilation> </system.web> </configuration> And with that you should get full IntelliSense. Note that if you add a BIN folder and you also have the templates in your Visual Studio project Visual Studio will complain about reference conflicts as it’s effectively seeing both the project references and the ones in the bin folder. So it’s probably a good idea to use one or the other but not both at the same time :-) Seeing IntelliSense in your Razor templates is a big help for users of your templates. If you’re shipping an application level scripting solution especially it’ll be real useful for your template consumers/users to be able to get some quick help on creating customized templates – after all that’s what templates are all about – easy customization. Making sure that everything is referenced in your bin folder and web.config is a good idea and it’s great to see that Visual Studio (and presumably WebMatrix/Visual Web Developer as well) will be able to pick up your custom IntelliSense in Razor templates.© Rick Strahl, West Wind Technologies, 2005-2011Posted in Razor  

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  • Movement prediction for non-shooters

    - by ShadowChaser
    I'm working on an isometric 2D game with moderate-scale multiplayer, approximately 20-30 players connected at once to a persistent server. I've had some difficulty getting a good movement prediction implementation in place. Physics/Movement The game doesn't have a true physics implementation, but uses the basic principles to implement movement. Rather than continually polling input, state changes (ie/ mouse down/up/move events) are used to change the state of the character entity the player is controlling. The player's direction (ie/ north-east) is combined with a constant speed and turned into a true 3D vector - the entity's velocity. In the main game loop, "Update" is called before "Draw". The update logic triggers a "physics update task" that tracks all entities with a non-zero velocity uses very basic integration to change the entities position. For example: entity.Position += entity.Velocity.Scale(ElapsedTime.Seconds) (where "Seconds" is a floating point value, but the same approach would work for millisecond integer values). The key point is that no interpolation is used for movement - the rudimentary physics engine has no concept of a "previous state" or "current state", only a position and velocity. State Change and Update Packets When the velocity of the character entity the player is controlling changes, a "move avatar" packet is sent to the server containing the entity's action type (stand, walk, run), direction (north-east), and current position. This is different from how 3D first person games work. In a 3D game the velocity (direction) can change frame to frame as the player moves around. Sending every state change would effectively transmit a packet per frame, which would be too expensive. Instead, 3D games seem to ignore state changes and send "state update" packets on a fixed interval - say, every 80-150ms. Since speed and direction updates occur much less frequently in my game, I can get away with sending every state change. Although all of the physics simulations occur at the same speed and are deterministic, latency is still an issue. For that reason, I send out routine position update packets (similar to a 3D game) but much less frequently - right now every 250ms, but I suspect with good prediction I can easily boost it towards 500ms. The biggest problem is that I've now deviated from the norm - all other documentation, guides, and samples online send routine updates and interpolate between the two states. It seems incompatible with my architecture, and I need to come up with a better movement prediction algorithm that is closer to a (very basic) "networked physics" architecture. The server then receives the packet and determines the players speed from it's movement type based on a script (Is the player able to run? Get the player's running speed). Once it has the speed, it combines it with the direction to get a vector - the entity's velocity. Some cheat detection and basic validation occurs, and the entity on the server side is updated with the current velocity, direction, and position. Basic throttling is also performed to prevent players from flooding the server with movement requests. After updating its own entity, the server broadcasts an "avatar position update" packet to all other players within range. The position update packet is used to update the client side physics simulations (world state) of the remote clients and perform prediction and lag compensation. Prediction and Lag Compensation As mentioned above, clients are authoritative for their own position. Except in cases of cheating or anomalies, the client's avatar will never be repositioned by the server. No extrapolation ("move now and correct later") is required for the client's avatar - what the player sees is correct. However, some sort of extrapolation or interpolation is required for all remote entities that are moving. Some sort of prediction and/or lag-compensation is clearly required within the client's local simulation / physics engine. Problems I've been struggling with various algorithms, and have a number of questions and problems: Should I be extrapolating, interpolating, or both? My "gut feeling" is that I should be using pure extrapolation based on velocity. State change is received by the client, client computes a "predicted" velocity that compensates for lag, and the regular physics system does the rest. However, it feels at odds to all other sample code and articles - they all seem to store a number of states and perform interpolation without a physics engine. When a packet arrives, I've tried interpolating the packet's position with the packet's velocity over a fixed time period (say, 200ms). I then take the difference between the interpolated position and the current "error" position to compute a new vector and place that on the entity instead of the velocity that was sent. However, the assumption is that another packet will arrive in that time interval, and it's incredibly difficult to "guess" when the next packet will arrive - especially since they don't all arrive on fixed intervals (ie/ state changes as well). Is the concept fundamentally flawed, or is it correct but needs some fixes / adjustments? What happens when a remote player stops? I can immediately stop the entity, but it will be positioned in the "wrong" spot until it moves again. If I estimate a vector or try to interpolate, I have an issue because I don't store the previous state - the physics engine has no way to say "you need to stop after you reach position X". It simply understands a velocity, nothing more complex. I'm reluctant to add the "packet movement state" information to the entities or physics engine, since it violates basic design principles and bleeds network code across the rest of the game engine. What should happen when entities collide? There are three scenarios - the controlling player collides locally, two entities collide on the server during a position update, or a remote entity update collides on the local client. In all cases I'm uncertain how to handle the collision - aside from cheating, both states are "correct" but at different time periods. In the case of a remote entity it doesn't make sense to draw it walking through a wall, so I perform collision detection on the local client and cause it to "stop". Based on point #2 above, I might compute a "corrected vector" that continually tries to move the entity "through the wall" which will never succeed - the remote avatar is stuck there until the error gets too high and it "snaps" into position. How do games work around this?

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  • how to continuously send data without blocking?

    - by Donal Rafferty
    I am trying to send rtp audio data from my Android application. I currently can send 1 RTP packet with the code below and I also have another class that extends Thread that listens to and receives RTP packets. My question is how do I continuously send my updated buffer through the packet payload without blocking the receiving thread? public void run() { isRecording = true; android.os.Process.setThreadPriority (android.os.Process.THREAD_PRIORITY_URGENT_AUDIO); int buffersize = AudioRecord.getMinBufferSize(8000, AudioFormat.CHANNEL_CONFIGURATION_MONO, AudioFormat.ENCODING_PCM_16BIT); Log.d("BUFFERSIZE","Buffer size = " + buffersize); arec = new AudioRecord(MediaRecorder.AudioSource.MIC, 8000, AudioFormat.CHANNEL_CONFIGURATION_MONO, AudioFormat.ENCODING_PCM_16BIT, buffersize); short[] readBuffer = new short[80]; byte[] buffer = new byte[160]; arec.startRecording(); while(arec.getRecordingState() == AudioRecord.RECORDSTATE_RECORDING){ int frames = arec.read(readBuffer, 0, 80); @SuppressWarnings("unused") int lenghtInBytes = codec.encode(readBuffer, 0, buffer, frames); RtpPacket rtpPacket = new RtpPacket(); rtpPacket.setV(2); rtpPacket.setX(0); rtpPacket.setM(0); rtpPacket.setPT(0); rtpPacket.setSSRC(123342345); rtpPacket.setPayload(buffer, 160); try { rtpSession2.sendRtpPacket(rtpPacket); } catch (UnknownHostException e) { // TODO Auto-generated catch block e.printStackTrace(); } catch (RtpException e) { // TODO Auto-generated catch block e.printStackTrace(); } catch (IOException e) { // TODO Auto-generated catch block e.printStackTrace(); } } } So when I send on one device and receive on another I get decent audio, but when I send and receive on both I get broken sound like its taking turns to send and receive audio. I have a feeling it could be to do with the while loop? it could be looping around in there and not letting anything else run?

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  • Downloading javascript Without Blocking

    - by doug
    The context: My question relates to improving web-page loading performance, and in particular the effect that javascript has on page-loading (resources/elements below the script are blocked from downloading/rendering). This problem is usually avoided/mitigated by placing the scripts at the bottom (eg, just before the tag). The code i am looking at is for web analytics. Placing it at the bottom reduces its accuracy; and because this script has no effect on the page's content, ie, it's not re-writing any part of the page--i want to move it inside the head. Just how to do that without ruining page-loading performance is the crux. From my research, i've found six techniques (w/ support among all or most of the major browsers) for downloading scripts so that they don't block down-page content from loading/rendering: (i) XHR + eval(); (ii) XHR + 'inject'; (iii) download the HTML-wrapped script as in iFrame; (iv) setting the script tag's 'async' flag to 'TRUE' (HTML 5 only); (v) setting the script tag's 'defer' attribute; and (vi) 'Script DOM Element'. It's the last of these i don't understand. The javascript to implement the pattern (vi) is: (function() { var q1 = document.createElement('script'); q1.src = 'http://www.my_site.com/q1.js' document.documentElement.firstChild.appendChild(q1) })(); Seems simple enough: inside this anonymous function, a script element is created, its 'src' element is set to it's location, then the script element is added to the DOM. But while each line is clear, it's still not clear to me how exactly this pattern allows script loading without blocking down-page elements/resources from rendering/loading?

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  • libcurl (c api) READFUNCTION for http PUT blocking forever

    - by Duane
    I am using libcurl for a RESTful library. I am having two problems with a PUT message, I am just trying to send a small content like "hello" via put. My READFUNCTION for PUT's blocks for a very large amount of time (minutes) when I follow the manual at curl.haxx.se and return a 0 indicating I have finished the content. (on os X) When I return something 0 this succeeds much faster (< 1 sec) When I run this on my linux machine (ubuntu 10.4) this blocking event appears to NEVER return when I return 0, if I change the behavior to return the size written libcurl appends all the data in the http body sending way more data and it fails with a "too much data" message from the server. my readfunction is below, any help would be greatly appreciated. I am using libcurl 7.20.1 typedef struct{ void *data; int body_size; int bytes_remaining; int bytes_written; } postdata; size_t readfunc(void *ptr, size_t size, size_t nmemb, void *stream) { if(stream) { postdata ud = (postdata)stream; if(ud->bytes_remaining) { if(ud->body_size > size*nmemb) { memcpy(ptr, ud->data+ud->bytes_written, size*nmemb); ud->bytes_written+=size+nmemb; ud->bytes_remaining = ud->body_size-size*nmemb; return size*nmemb; } else { memcpy(ptr, ud->data+ud->bytes_written, ud->bytes_remaining); ud->bytes_remaining=0; return 0; } }

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  • Is memory allocation in linux non-blocking?

    - by Mark
    I am curious to know if the allocating memory using a default new operator is a non-blocking operation. e.g. struct Node { int a,b; }; ... Node foo = new Node(); If multiple threads tried to create a new Node and if one of them was suspended by the OS in the middle of allocation, would it block other threads from making progress? The reason why I ask is because I had a concurrent data structure that created new nodes. I then modified the algorithm to recycle the nodes. The throughput performance of the two algorithms was virtually identical on a 24 core machine. However, I then created an interference program that ran on all the system cores in order to create as much OS pre-emption as possible. The throughput performance of the algorithm that created new nodes decreased by a factor of 5 relative the the algorithm that recycled nodes. I'm curious to know why this would occur. Thanks. *Edit : pointing me to the code for the c++ memory allocator for linux would be helpful as well. I tried looking before posting this question, but had trouble finding it.

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  • Hardening non-root standalone Linux Tomcat install

    - by NoozNooz42
    I want to know if you have any tips as to how to strengthen the security of a non-root install of Tomcat in standalone mode once Tomcat is already installed in a non-root account, in standalone mode. I precise this because, for example, I'm not at all interested by the answers given here (because both Java and Tomcat requires root priviledges there to be installed and I've got zero interest in running jsvc): http://serverfault.com/questions/43765 So far, here's what I've done for my non-root standalone Tomcat 6 install: download and install the JRE .bin provided by Oracle/Sun (no need to be root here) (no need for a full JDK anymore right seen that Jasper [Tomcat's JSP engine] has its own compiler now right?) download and tar -xzf tomcat 6 (no need to be root here) set up transparent port-forwarding (must be root here) Note that my distribution is a Debian one and I have exactly zero interest in downloading Debian package / backports / whatever... Because, once again, I DO NOT want to need to be root to install Java & Tomcat. The only moment I needed to be root was to configure the firewall to transparently do the port forwarding 80 <-- 8080 and 443 <-- 8443. I then deleted all the default webapps but one: cd ~/apache-tomcat-6.0.26/webapps rm -rf docs rm -rf examples/ rm -rf manager/ rm -rf ROOT/ What about the directory ~/apache-tomcat-6.0.26/webapps/host-manager, do I need it or can I delete it? So, once I've installed Tomcat standalone in a non-root account (and taken into account that I don't want to enter the root password anymore and that I don't plan to install the whole Apache shebang), what more can I do? Are there connectors I can disable? (how?)

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