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• Help me understand a part of Java Language Specification

  - by Software Engeneering Learner

  I'm reading part 17.2.1 of Java language specification: http://docs.oracle.com/javase/specs/jls/se7/html/jls-17.html#jls-17.2.1 I won't copy a text, it's too long, but I would like to know, why for third step of sequence they're saying that If thread t was removed from m's wait set in step 2 due to an interrupt Thread couldn't get to step 2 it wasn't removed from wait set, because it written for the step 1: Thread t does not execute any further instructions until it has been removed from m's wait set Thus thread can't be removed from wait set in step 2 whatever it's due to, because it was already removed. Please help me understand this.

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• tcp msl timeout

  - by iamrohitbanga

  The following is given in the book TCP IP Illustrated by Stevens Quiet Time Concept The 2MSL wait provides protection against delayed segments from an earlier incarnation of a connection from being interpreted as part of a new connection that uses the same local and foreign IP addresses and port numbers. But this works only if a host with connections in the 2MSL wait does not crash. What if a host with ports in the 2MSL wait crashes, reboots within MSL seconds, and immediately establishes new connections using the same local and foreign IP addresses and port numbers corresponding to the local ports that were in the 2MSL wait before the crash? In this scenario, delayed segments from the connections that existed before the crash can be misinterpreted as belonging to the new connections created after the reboot. This can happen regardless of how the initial sequence number is chosen after the reboot. To protect against this scenario, RFC 793 states that TCP should not create any connections for MSL seconds after rebooting. This is called the quiet time Few implementations abide by this since most hosts take longer than MSL seconds to reboot after a crash. Do operating systems wait for 2MSL seconds now after a reboot before initiating a TCP connection. The boot times are also less these days. Although the ports and sequence numbers are random but is this wait implemented in Linux?

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• PTLQueue : a scalable bounded-capacity MPMC queue

  - by Dave

  Title: Fast concurrent MPMC queue -- I've used the following concurrent queue algorithm enough that it warrants a blog entry. I'll sketch out the design of a fast and scalable multiple-producer multiple-consumer (MPSC) concurrent queue called PTLQueue. The queue has bounded capacity and is implemented via a circular array. Bounded capacity can be a useful property if there's a mismatch between producer rates and consumer rates where an unbounded queue might otherwise result in excessive memory consumption by virtue of the container nodes that -- in some queue implementations -- are used to hold values. A bounded-capacity queue can provide flow control between components. Beware, however, that bounded collections can also result in resource deadlock if abused. The put() and take() operators are partial and wait for the collection to become non-full or non-empty, respectively. Put() and take() do not allocate memory, and are not vulnerable to the ABA pathologies. The PTLQueue algorithm can be implemented equally well in C/C++ and Java. Partial operators are often more convenient than total methods. In many use cases if the preconditions aren't met, there's nothing else useful the thread can do, so it may as well wait via a partial method. An exception is in the case of work-stealing queues where a thief might scan a set of queues from which it could potentially steal. Total methods return ASAP with a success-failure indication. (It's tempting to describe a queue or API as blocking or non-blocking instead of partial or total, but non-blocking is already an overloaded concurrency term. Perhaps waiting/non-waiting or patient/impatient might be better terms). It's also trivial to construct partial operators by busy-waiting via total operators, but such constructs may be less efficient than an operator explicitly and intentionally designed to wait. A PTLQueue instance contains an array of slots, where each slot has volatile Turn and MailBox fields. The array has power-of-two length allowing mod/div operations to be replaced by masking. We assume sensible padding and alignment to reduce the impact of false sharing. (On x86 I recommend 128-byte alignment and padding because of the adjacent-sector prefetch facility). Each queue also has PutCursor and TakeCursor cursor variables, each of which should be sequestered as the sole occupant of a cache line or sector. You can opt to use 64-bit integers if concerned about wrap-around aliasing in the cursor variables. Put(null) is considered illegal, but the caller or implementation can easily check for and convert null to a distinguished non-null proxy value if null happens to be a value you'd like to pass. Take() will accordingly convert the proxy value back to null. An advantage of PTLQueue is that you can use atomic fetch-and-increment for the partial methods. We initialize each slot at index I with (Turn=I, MailBox=null). Both cursors are initially 0. All shared variables are considered "volatile" and atomics such as CAS and AtomicFetchAndIncrement are presumed to have bidirectional fence semantics. Finally T is the templated type. I've sketched out a total tryTake() method below that allows the caller to poll the queue. tryPut() has an analogous construction. Zebra stripping : alternating row colors for nice-looking code listings. See also google code "prettify" : https://code.google.com/p/google-code-prettify/ Prettify is a javascript module that yields the HTML/CSS/JS equivalent of pretty-print. -- pre:nth-child(odd) { background-color:#ff0000; } pre:nth-child(even) { background-color:#0000ff; } border-left: 11px solid #ccc; margin: 1.7em 0 1.7em 0.3em; background-color:#BFB; font-size:12px; line-height:65%; " // PTLQueue : Put(v) : // producer : partial method - waits as necessary assert v != null assert Mask = 1 && (Mask & (Mask+1)) == 0 // Document invariants // doorway step // Obtain a sequence number -- ticket // As a practical concern the ticket value is temporally unique // The ticket also identifies and selects a slot auto tkt = AtomicFetchIncrement (&PutCursor, 1) slot * s = &Slots[tkt & Mask] // waiting phase : // wait for slot's generation to match the tkt value assigned to this put() invocation. // The "generation" is implicitly encoded as the upper bits in the cursor // above those used to specify the index : tkt div (Mask+1) // The generation serves as an epoch number to identify a cohort of threads // accessing disjoint slots while s-Turn != tkt : Pause assert s-MailBox == null s-MailBox = v // deposit and pass message Take() : // consumer : partial method - waits as necessary auto tkt = AtomicFetchIncrement (&TakeCursor,1) slot * s = &Slots[tkt & Mask] // 2-stage waiting : // First wait for turn for our generation // Acquire exclusive "take" access to slot's MailBox field // Then wait for the slot to become occupied while s-Turn != tkt : Pause // Concurrency in this section of code is now reduced to just 1 producer thread // vs 1 consumer thread. // For a given queue and slot, there will be most one Take() operation running // in this section. // Consumer waits for producer to arrive and make slot non-empty // Extract message; clear mailbox; advance Turn indicator // We have an obvious happens-before relation : // Put(m) happens-before corresponding Take() that returns that same "m" for T v = s-MailBox if v != null : s-MailBox = null ST-ST barrier s-Turn = tkt + Mask + 1 // unlock slot to admit next producer and consumer return v Pause tryTake() : // total method - returns ASAP with failure indication for auto tkt = TakeCursor slot * s = &Slots[tkt & Mask] if s-Turn != tkt : return null T v = s-MailBox // presumptive return value if v == null : return null // ratify tkt and v values and commit by advancing cursor if CAS (&TakeCursor, tkt, tkt+1) != tkt : continue s-MailBox = null ST-ST barrier s-Turn = tkt + Mask + 1 return v The basic idea derives from the Partitioned Ticket Lock "PTL" (US20120240126-A1) and the MultiLane Concurrent Bag (US8689237). The latter is essentially a circular ring-buffer where the elements themselves are queues or concurrent collections. You can think of the PTLQueue as a partitioned ticket lock "PTL" augmented to pass values from lock to unlock via the slots. Alternatively, you could conceptualize of PTLQueue as a degenerate MultiLane bag where each slot or "lane" consists of a simple single-word MailBox instead of a general queue. Each lane in PTLQueue also has a private Turn field which acts like the Turn (Grant) variables found in PTL. Turn enforces strict FIFO ordering and restricts concurrency on the slot mailbox field to at most one simultaneous put() and take() operation. PTL uses a single "ticket" variable and per-slot Turn (grant) fields while MultiLane has distinct PutCursor and TakeCursor cursors and abstract per-slot sub-queues. Both PTL and MultiLane advance their cursor and ticket variables with atomic fetch-and-increment. PTLQueue borrows from both PTL and MultiLane and has distinct put and take cursors and per-slot Turn fields. Instead of a per-slot queues, PTLQueue uses a simple single-word MailBox field. PutCursor and TakeCursor act like a pair of ticket locks, conferring "put" and "take" access to a given slot. PutCursor, for instance, assigns an incoming put() request to a slot and serves as a PTL "Ticket" to acquire "put" permission to that slot's MailBox field. To better explain the operation of PTLQueue we deconstruct the operation of put() and take() as follows. Put() first increments PutCursor obtaining a new unique ticket. That ticket value also identifies a slot. Put() next waits for that slot's Turn field to match that ticket value. This is tantamount to using a PTL to acquire "put" permission on the slot's MailBox field. Finally, having obtained exclusive "put" permission on the slot, put() stores the message value into the slot's MailBox. Take() similarly advances TakeCursor, identifying a slot, and then acquires and secures "take" permission on a slot by waiting for Turn. Take() then waits for the slot's MailBox to become non-empty, extracts the message, and clears MailBox. Finally, take() advances the slot's Turn field, which releases both "put" and "take" access to the slot's MailBox. Note the asymmetry : put() acquires "put" access to the slot, but take() releases that lock. At any given time, for a given slot in a PTLQueue, at most one thread has "put" access and at most one thread has "take" access. This restricts concurrency from general MPMC to 1-vs-1. We have 2 ticket locks -- one for put() and one for take() -- each with its own "ticket" variable in the form of the corresponding cursor, but they share a single "Grant" egress variable in the form of the slot's Turn variable. Advancing the PutCursor, for instance, serves two purposes. First, we obtain a unique ticket which identifies a slot. Second, incrementing the cursor is the doorway protocol step to acquire the per-slot mutual exclusion "put" lock. The cursors and operations to increment those cursors serve double-duty : slot-selection and ticket assignment for locking the slot's MailBox field. At any given time a slot MailBox field can be in one of the following states: empty with no pending operations -- neutral state; empty with one or more waiting take() operations pending -- deficit; occupied with no pending operations; occupied with one or more waiting put() operations -- surplus; empty with a pending put() or pending put() and take() operations -- transitional; or occupied with a pending take() or pending put() and take() operations -- transitional. The partial put() and take() operators can be implemented with an atomic fetch-and-increment operation, which may confer a performance advantage over a CAS-based loop. In addition we have independent PutCursor and TakeCursor cursors. Critically, a put() operation modifies PutCursor but does not access the TakeCursor and a take() operation modifies the TakeCursor cursor but does not access the PutCursor. This acts to reduce coherence traffic relative to some other queue designs. It's worth noting that slow threads or obstruction in one slot (or "lane") does not impede or obstruct operations in other slots -- this gives us some degree of obstruction isolation. PTLQueue is not lock-free, however. The implementation above is expressed with polite busy-waiting (Pause) but it's trivial to implement per-slot parking and unparking to deschedule waiting threads. It's also easy to convert the queue to a more general deque by replacing the PutCursor and TakeCursor cursors with Left/Front and Right/Back cursors that can move either direction. Specifically, to push and pop from the "left" side of the deque we would decrement and increment the Left cursor, respectively, and to push and pop from the "right" side of the deque we would increment and decrement the Right cursor, respectively. We used a variation of PTLQueue for message passing in our recent OPODIS 2013 paper. ul { list-style:none; padding-left:0; padding:0; margin:0; margin-left:0; } ul#myTagID { padding: 0px; margin: 0px; list-style:none; margin-left:0;} -- -- There's quite a bit of related literature in this area. I'll call out a few relevant references: Wilson's NYU Courant Institute UltraComputer dissertation from 1988 is classic and the canonical starting point : Operating System Data Structures for Shared-Memory MIMD Machines with Fetch-and-Add. Regarding provenance and priority, I think PTLQueue or queues effectively equivalent to PTLQueue have been independently rediscovered a number of times. See CB-Queue and BNPBV, below, for instance. But Wilson's dissertation anticipates the basic idea and seems to predate all the others. Gottlieb et al : Basic Techniques for the Efficient Coordination of Very Large Numbers of Cooperating Sequential Processors Orozco et al : CB-Queue in Toward high-throughput algorithms on many-core architectures which appeared in TACO 2012. Meneghin et al : BNPVB family in Performance evaluation of inter-thread communication mechanisms on multicore/multithreaded architecture Dmitry Vyukov : bounded MPMC queue (highly recommended) Alex Otenko : US8607249 (highly related). John Mellor-Crummey : Concurrent queues: Practical fetch-and-phi algorithms. Technical Report 229, Department of Computer Science, University of Rochester Thomasson : FIFO Distributed Bakery Algorithm (very similar to PTLQueue). Scott and Scherer : Dual Data Structures I'll propose an optimization left as an exercise for the reader. Say we wanted to reduce memory usage by eliminating inter-slot padding. Such padding is usually "dark" memory and otherwise unused and wasted. But eliminating the padding leaves us at risk of increased false sharing. Furthermore lets say it was usually the case that the PutCursor and TakeCursor were numerically close to each other. (That's true in some use cases). We might still reduce false sharing by incrementing the cursors by some value other than 1 that is not trivially small and is coprime with the number of slots. Alternatively, we might increment the cursor by one and mask as usual, resulting in a logical index. We then use that logical index value to index into a permutation table, yielding an effective index for use in the slot array. The permutation table would be constructed so that nearby logical indices would map to more distant effective indices. (Open question: what should that permutation look like? Possibly some perversion of a Gray code or De Bruijn sequence might be suitable). As an aside, say we need to busy-wait for some condition as follows : "while C == 0 : Pause". Lets say that C is usually non-zero, so we typically don't wait. But when C happens to be 0 we'll have to spin for some period, possibly brief. We can arrange for the code to be more machine-friendly with respect to the branch predictors by transforming the loop into : "if C == 0 : for { Pause; if C != 0 : break; }". Critically, we want to restructure the loop so there's one branch that controls entry and another that controls loop exit. A concern is that your compiler or JIT might be clever enough to transform this back to "while C == 0 : Pause". You can sometimes avoid this by inserting a call to a some type of very cheap "opaque" method that the compiler can't elide or reorder. On Solaris, for instance, you could use :"if C == 0 : { gethrtime(); for { Pause; if C != 0 : break; }}". It's worth noting the obvious duality between locks and queues. If you have strict FIFO lock implementation with local spinning and succession by direct handoff such as MCS or CLH,then you can usually transform that lock into a queue. Hidden commentary and annotations - invisible : * And of course there's a well-known duality between queues and locks, but I'll leave that topic for another blog post. * Compare and contrast : PTLQ vs PTL and MultiLane * Equivalent : Turn; seq; sequence; pos; position; ticket * Put = Lock; Deposit Take = identify and reserve slot; wait; extract & clear; unlock * conceptualize : Distinct PutLock and TakeLock implemented as ticket lock or PTL Distinct arrival cursors but share per-slot "Turn" variable provides exclusive role-based access to slot's mailbox field put() acquires exclusive access to a slot for purposes of "deposit" assigns slot round-robin and then acquires deposit access rights/perms to that slot take() acquires exclusive access to slot for purposes of "withdrawal" assigns slot round-robin and then acquires withdrawal access rights/perms to that slot At any given time, only one thread can have withdrawal access to a slot at any given time, only one thread can have deposit access to a slot Permissible for T1 to have deposit access and T2 to simultaneously have withdrawal access * round-robin for the purposes of; role-based; access mode; access role mailslot; mailbox; allocate/assign/identify slot rights; permission; license; access permission; * PTL/Ticket hybrid Asymmetric usage ; owner oblivious lock-unlock pairing K-exclusion add Grant cursor pass message m from lock to unlock via Slots[] array Cursor performs 2 functions : + PTL ticket + Assigns request to slot in round-robin fashion Deconstruct protocol : explication put() : allocate slot in round-robin fashion acquire PTL for "put" access store message into slot associated with PTL index take() : Acquire PTL for "take" access // doorway step seq = fetchAdd (&Grant, 1) s = &Slots[seq & Mask] // waiting phase while s-Turn != seq : pause Extract : wait for s-mailbox to be full v = s-mailbox s-mailbox = null Release PTL for both "put" and "take" access s-Turn = seq + Mask + 1 * Slot round-robin assignment and lock "doorway" protocol leverage the same cursor and FetchAdd operation on that cursor FetchAdd (&Cursor,1) + round-robin slot assignment and dispersal + PTL/ticket lock "doorway" step waiting phase is via "Turn" field in slot * PTLQueue uses 2 cursors -- put and take. Acquire "put" access to slot via PTL-like lock Acquire "take" access to slot via PTL-like lock 2 locks : put and take -- at most one thread can access slot's mailbox Both locks use same "turn" field Like multilane : 2 cursors : put and take slot is simple 1-capacity mailbox instead of queue Borrow per-slot turn/grant from PTL Provides strict FIFO Lock slot : put-vs-put take-vs-take at most one put accesses slot at any one time at most one put accesses take at any one time reduction to 1-vs-1 instead of N-vs-M concurrency Per slot locks for put/take Release put/take by advancing turn * is instrumental in ... * P-V Semaphore vs lock vs K-exclusion * See also : FastQueues-excerpt.java dice-etc/queue-mpmc-bounded-blocking-circular-xadd/ * PTLQueue is the same as PTLQB - identical * Expedient return; ASAP; prompt; immediately * Lamport's Bakery algorithm : doorway step then waiting phase Threads arriving at doorway obtain a unique ticket number Threads enter in ticket order * In the terminology of Reed and Kanodia a ticket lock corresponds to the busy-wait implementation of a semaphore using an eventcount and a sequencer It can also be thought of as an optimization of Lamport's bakery lock was designed for fault-tolerance rather than performance Instead of spinning on the release counter, processors using a bakery lock repeatedly examine the tickets of their peers --

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• Non-reentrant C# timer

  - by Oak

  I'm trying to invoke a method f() every t time, but if the previous invocation of f() has not finished yet, wait until it's finished. I've read a bit about the available timers (this is a useful link) but couldn't find any good way of doing what I want, save for manually writing it all. Any help about how to achieve this will be appreciated, though I fear I might not be able to find a simple solution using timers. To clarify, if x is one second, and f() runs the arbitrary durations I've written below, then: Step Operation Time taken 1 wait 1s 2 f() 0.6s 3 wait 0.4s (because f already took 0.6 seconds) 4 f() 10s 5 wait 0s (we're late) 6 f() 0.3s 7 wait 0.7s (we can disregard the debt from step 4) Notice that the nature of this timer is that f() will not need to be safe regarding re-entrance, and a thread pool of size 1 is enough here.

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• Lightweight alternative to Manual/AutoResetEvent in C#

  - by sweetlilmre

  Hi, I have written what I hope is a lightweight alternative to using the ManualResetEvent and AutoResetEvent classes in C#/.NET. The reasoning behind this was to have Event like functionality without the weight of using a kernel locking object. Although the code seems to work well in both testing and production, getting this kind of thing right for all possibilities can be a fraught undertaking and I would humbly request any constructive comments and or criticism from the StackOverflow crowd on this. Hopefully (after review) this will be useful to others. Usage should be similar to the Manual/AutoResetEvent classes with Notify() used for Set(). Here goes: using System; using System.Threading; public class Signal { private readonly object _lock = new object(); private readonly bool _autoResetSignal; private bool _notified; public Signal() : this(false, false) { } public Signal(bool initialState, bool autoReset) { _autoResetSignal = autoReset; _notified = initialState; } public virtual void Notify() { lock (_lock) { // first time? if (!_notified) { // set the flag _notified = true; // unblock a thread which is waiting on this signal Monitor.Pulse(_lock); } } } public void Wait() { Wait(Timeout.Infinite); } public virtual bool Wait(int milliseconds) { lock (_lock) { bool ret = true; // this check needs to be inside the lock otherwise you can get nailed // with a race condition where the notify thread sets the flag AFTER // the waiting thread has checked it and acquires the lock and does the // pulse before the Monitor.Wait below - when this happens the caller // will wait forever as he "just missed" the only pulse which is ever // going to happen if (!_notified) { ret = Monitor.Wait(_lock, milliseconds); } if (_autoResetSignal) { _notified = false; } return (ret); } } }

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• phablet-flash aborting while installing Ubuntu Touch on Nexus 4

  - by Till B

  I have a Nexus 4 with Android 4.3 installed and I want to flash it to Ubuntu Touch. My system is Ubuntu 12.04, running inside a virtual machine on Mac OS 10.5.8. To use the VM, I opened an NAT bridge and forwarded port 5037 for adb, I can see the Nexus with adb and e.g. use the adb shell into it. USB ports are also forwarded to the VM. I follow these instructions to the letter. My bootloader is unlocked, just as it was described in the instructions. Now I encounter different issues, when executing sudo phablet-flash ubuntu-system --no-backup. On the first run, it got stuck in this state: INFO:phablet-flash:Decompressing partitions/recovery.img from /home/till/Downloads/phablet-flash/imageupdates/pool/device-5ba3031cb0d6fc624848266edba781e3e821b6e1e8dd21105725f0ab26077d0a.tar.xz INFO:phablet-flash:Restarting device... wait INFO:phablet-flash:Restarting device... wait complete INFO:phablet-flash:Booting /tmp/tmpMSN8bm/partitions/recovery.img < waiting for device > downloading 'boot.img'... OKAY [ 1.772s] booting... OKAY [ 0.005s] finished. total time: 1.779s INFO:phablet-flash:Waiting for recovery image to boot The following happened: around the line "INFO:phablet-flash: Restarting...", it rebooted into the bootloader. The bootloader shows only for two seconds, then the screen goes off and the phone stays off. But I do notice, that the screen is not off - it is just black, but the background light is on. If I wait long enough, phablet-flash aborts with ERROR:phablet-flash:Wait for recovery expired On the second try, I wanted to manually start the bootloader and choose "Recovery mode". Pressing "volume down+power" at first did nothing. Releasing the buttons and then pressing them again brought me into the bootloder. After choosing "Recovery mode", phablet-flash continued and after a while aborted with the following output: INFO:phablet-flash:Wait for recovery image to boot complete INFO:phablet-flash:Clearing /data and /cache INFO:phablet-flash:Pushing /home/till/Downloads/phablet-flash/imageupdates/pool/ubuntu-2b5345658b58e55207c4a4e7b6b3d8cd4f3d9a3187d2448fc9020c884234bac0.tar.xz to /cache/recovery/ failed to copy '/home/till/Downloads/phablet-flash/imageupdates/pool/ubuntu-2b5345658b58e55207c4a4e7b6b3d8cd4f3d9a3187d2448fc9020c884234bac0.tar.xz' to '/cache/recovery/': Permission denied ERROR:phablet-flash:Command 'adb push /home/till/Downloads/phablet-flash/imageupdates/pool/ubuntu-2b5345658b58e55207c4a4e7b6b3d8cd4f3d9a3187d2448fc9020c884234bac0.tar.xz /cache/recovery/' returned non-zero exit status 1 Removing directory /tmp/tmpDnbz6N Removing directory /tmp/tmpth4L6w What can I do to properly flash my phone with Ubuntu Touch? I noticed that adb does not show the phone in recovery mode: Typing adb devices, when the Nexus 4 is in recovery mode, shows the serial number and the state device, where it should show recovery. Should the phone be rooted? This is not mentioned in the instructions.

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• Sound Complete Not Firing (AS3)

  - by JasonMc92

  I have a bit of a quandary. I need to call a function inside a MovieClip once a particular sound has finished playing. The sound is played via a sound channel in an external class which I have imported. Playback is working perfectly. Here is the relevent code from my external class, Sonus. public var SFXPRChannel:SoundChannel = new SoundChannel; var SFXPRfishbeg:Sound = new sfxpr_fishbeg(); var SFXPRfishmid:Sound = new sfxpr_fishmid(); var SFXPRfishend3:Sound = new sfxpr_fishend3(); var SFXPRfishend4:Sound = new sfxpr_fishend4() public function PlayPrompt(promptname:String):void { var sound:String = "SFXPR" + promptname; SFXPRChannel = this[sound].play(); } This is called via an import in the document class "osr", thus I access it in my project via "osr.Sonus.---" In my project, I have the following line of code. osr.Sonus.SFXPRChannel.addEventListener(Event.SOUND_COMPLETE, promptIsFinished); function prompt():void { var level = osr.Gradua.Fetch("fish", "arr_con_level"); Wait(true); switch(level) { case 1: osr.Sonus.PlayPrompt("fishbeg"); break; case 2: osr.Sonus.PlayPrompt("fishmid"); break; case 3: osr.Sonus.PlayPrompt("fishend3"); break; case 4: osr.Sonus.PlayPrompt("fishend4"); break; } } function Wait(yesno):void { gui.Wait(yesno); } function promptIsFinished(evt:Event):void { Wait(false); } osr.Sonus.PlayPrompt(...) and gui.Wait(...) both work perfectly, as I use them in other contexts in this part of the project without error. Basically, after the sound finishes playing, I need Wait(false); to be called, but the event listener does not appear to be "hearing" the SOUND_COMPLETE event. Did I make a mistake somewhere? For the record, due to my project structure, I cannot call the appropriate Wait(...) function from within Sonus. Help?

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• Java thread dump where main thread has no call stack? (jsvc)

  - by dwhsix

  We have a java process running as a daemon (under jsvc). Every several days it just stops doing any work; output to the logfile stops (it is pretty verbose, on 5-minute intervals) and it consumes no CPU or IO. There are no exceptions logged in the logfile nor in syserr or sysout. The last log statement is just prior to a db commit being done, but there is no open connection on the db server (MySQL) and reviewing the code, there should always be additional log output after that, even if it had encountered an exception that was going to bubble up. The most curious thing I find is that in the thread dump (included below), there's no thread in our code at all, and the main thread seems to have no context whatsoever: "main" prio=10 tid=0x0000000000614000 nid=0x445d runnable [0x0000000000000000] java.lang.Thread.State: RUNNABLE As noted earlier, this is a daemon process running using jsvc, but I don't know if that has anything to do with it (I can restructure the code to also allow running it directly, to test). Any suggestions on what might be happening here? Thanks... dwh Full thread dump: Full thread dump Java HotSpot(TM) 64-Bit Server VM (14.2-b01 mixed mode): "MySQL Statement Cancellation Timer" daemon prio=10 tid=0x00002aaaf81b8800 nid=0x447b in Object.wait() [0x00002aaaf6a22000] java.lang.Thread.State: WAITING (on object monitor) at java.lang.Object.wait(Native Method) - waiting on <0x00002aaab5556d50> (a java.util.TaskQueue) at java.lang.Object.wait(Object.java:485) at java.util.TimerThread.mainLoop(Timer.java:483) - locked <0x00002aaab5556d50> (a java.util.TaskQueue) at java.util.TimerThread.run(Timer.java:462) "Low Memory Detector" daemon prio=10 tid=0x00000000006a4000 nid=0x4479 runnable [0x0000000000000000] java.lang.Thread.State: RUNNABLE "CompilerThread1" daemon prio=10 tid=0x00000000006a1000 nid=0x4477 waiting on condition [0x0000000000000000] java.lang.Thread.State: RUNNABLE "CompilerThread0" daemon prio=10 tid=0x000000000069d000 nid=0x4476 waiting on condition [0x0000000000000000] java.lang.Thread.State: RUNNABLE "Signal Dispatcher" daemon prio=10 tid=0x000000000069b000 nid=0x4465 waiting on condition [0x0000000000000000] java.lang.Thread.State: RUNNABLE "Finalizer" daemon prio=10 tid=0x0000000000678800 nid=0x4464 in Object.wait() [0x00002aaaf61d6000] java.lang.Thread.State: WAITING (on object monitor) at java.lang.Object.wait(Native Method) - waiting on <0x00002aaab54a1cb8> (a java.lang.ref.ReferenceQueue$Lock) at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:118) - locked <0x00002aaab54a1cb8> (a java.lang.ref.ReferenceQueue$Lock) at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:134) at java.lang.ref.Finalizer$FinalizerThread.run(Finalizer.java:159) "Reference Handler" daemon prio=10 tid=0x0000000000676800 nid=0x4463 in Object.wait() [0x00002aaaf60d5000] java.lang.Thread.State: WAITING (on object monitor) at java.lang.Object.wait(Native Method) - waiting on <0x00002aaab54a1cf0> (a java.lang.ref.Reference$Lock) at java.lang.Object.wait(Object.java:485) at java.lang.ref.Reference$ReferenceHandler.run(Reference.java:116) - locked <0x00002aaab54a1cf0> (a java.lang.ref.Reference$Lock) "main" prio=10 tid=0x0000000000614000 nid=0x445d runnable [0x0000000000000000] java.lang.Thread.State: RUNNABLE "VM Thread" prio=10 tid=0x0000000000670000 nid=0x4462 runnable "GC task thread#0 (ParallelGC)" prio=10 tid=0x000000000061e000 nid=0x445e runnable "GC task thread#1 (ParallelGC)" prio=10 tid=0x0000000000620000 nid=0x445f runnable "GC task thread#2 (ParallelGC)" prio=10 tid=0x0000000000622000 nid=0x4460 runnable "GC task thread#3 (ParallelGC)" prio=10 tid=0x0000000000623800 nid=0x4461 runnable "VM Periodic Task Thread" prio=10 tid=0x00000000006a6800 nid=0x447a waiting on condition JNI global references: 797 Heap PSYoungGen total 162944K, used 48388K [0x00002aaadff40000, 0x00002aaaf2ab0000, 0x00002aaaf5490000) eden space 102784K, 47% used [0x00002aaadff40000,0x00002aaae2e81170,0x00002aaae63a0000) from space 60160K, 0% used [0x00002aaaeb850000,0x00002aaaeb850000,0x00002aaaef310000) to space 86720K, 0% used [0x00002aaae63a0000,0x00002aaae63a0000,0x00002aaaeb850000) PSOldGen total 699072K, used 699072K [0x00002aaab5490000, 0x00002aaadff40000, 0x00002aaadff40000) object space 699072K, 100% used [0x00002aaab5490000,0x00002aaadff40000,0x00002aaadff40000) PSPermGen total 21248K, used 9252K [0x00002aaab0090000, 0x00002aaab1550000, 0x00002aaab5490000) object space 21248K, 43% used [0x00002aaab0090000,0x00002aaab09993e8,0x00002aaab1550000)

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• Why MySQL sat for 2 minutes doing nothing?

  - by Alex R

  This was a one-time thing, not reproducible... But I saved the show innodb status output. Can anybody tell what's going on here? The simple insert took almost 3 minutes to complete. | InnoDB | | ===================================== 110201 15:58:10 INNODB MONITOR OUTPUT ===================================== Per second averages calculated from the last 34 seconds ---------- SEMAPHORES ---------- OS WAIT ARRAY INFO: reservation count 11963, signal count 11766 --Thread 1824 has waited at .\btr\btr0cur.c line 443 for 118.00 seconds the sema phore: S-lock on RW-latch at 09D6453C created in file .\buf\buf0buf.c line 550 a writer (thread id 1824) has reserved it in mode wait exclusive number of readers 1, waiters flag 1 Last time read locked in file .\buf\buf0flu.c line 599 Last time write locked in file .\btr\btr0cur.c line 443 Mutex spin waits 0, rounds 527817, OS waits 7133 RW-shared spins 2532, OS waits 1226; RW-excl spins 1652, OS waits 1118 ------------ TRANSACTIONS ------------ Trx id counter 0 95830 Purge done for trx's n:o < 0 95814 undo n:o < 0 0 History list length 11 LIST OF TRANSACTIONS FOR EACH SESSION: ---TRANSACTION 0 0, not started, OS thread id 3704 MySQL thread id 551, query id 2702112 localhost 127.0.0.1 root show innodb status ---TRANSACTION 0 95829, not started, OS thread id 3132 MySQL thread id 534, query id 2702020 localhost 127.0.0.1 root ---TRANSACTION 0 95828, not started, OS thread id 3152 MySQL thread id 527, query id 2701973 localhost 127.0.0.1 root ---TRANSACTION 0 95827, ACTIVE 118 sec, OS thread id 1824 inserting, thread decl ared inside InnoDB 500 mysql tables in use 1, locked 1 1 lock struct(s), heap size 320, 0 row lock(s) MySQL thread id 526, query id 2701972 localhost 127.0.0.1 root update INSERT INTO log_searchcriteria (userid,search_criteria,date,search_type) VALUES ( NAME_CONST('userid',NULL), NAME_CONST('search_criteria',_latin1' SELECT SQL_C ALC_FOUND_ROWS idx_search.CTCX_LATITUDE, idx_search.CTCX_LONGITUDE, idx_search.b uilding_id, idx_search.LN_LIST_NUMBER, idx_search.LP_LIST_PRICE, idx_search.HSN_ ADRESS_HOUSE_NUMBER, idx_search.STR_ADDRESS_STREET, idx_search.CP_ADDRESS_COMPAS S_POINT, idx_search.UN_UNIT, idx_search.CIT_CITY, idx_search.ZP_ZIP_CODE, idx_se arch.AR_AREA_NAME, idx_search.BR_BEDROOMS, idx_search.BTH_BATHS, idx_search.ST_S TATUS, idx_search.CTCX_STYLE_TYPE, idx_s -------- FILE I/O -------- I/O thread 0 state: wait Windows aio (insert buffer thread) I/O thread 1 state: wait Windows aio (log thread) I/O thread 2 state: wait Windows aio (read thread) I/O thread 3 state: wait Windows aio (write thread) Pending normal aio reads: 0, aio writes: 1, ibuf aio reads: 0, log i/o's: 0, sync i/o's: 0 Pending flushes (fsync) log: 0; buffer pool: 0 151006 OS file reads, 120758 OS file writes, 6844 OS fsyncs 0.00 reads/s, 0 avg bytes/read, 0.00 writes/s, 0.00 fsyncs/s ------------------------------------- INSERT BUFFER AND ADAPTIVE HASH INDEX ------------------------------------- Ibuf: size 1, free list len 5, seg size 7, 24664 inserts, 24664 merged recs, 4612 merges Hash table size 553253, node heap has 629 buffer(s) 0.00 hash searches/s, 0.00 non-hash searches/s --- LOG --- Log sequence number 5 2318193115 Log flushed up to 5 2318193115 Last checkpoint at 5 2318129891 0 pending log writes, 0 pending chkp writes 3036 log i/o's done, 0.00 log i/o's/second ---------------------- BUFFER POOL AND MEMORY ---------------------- Total memory allocated 213459462; in additional pool allocated 1720192 Dictionary memory allocated 240416 Buffer pool size 8192 Free buffers 0 Database pages 7563 Modified db pages 18 Pending reads 0 Pending writes: LRU 0, flush list 18, single page 0 Pages read 150973, created 28788, written 115137 0.00 reads/s, 0.00 creates/s, 0.00 writes/s No buffer pool page gets since the last printout -------------- ROW OPERATIONS -------------- 1 queries inside InnoDB, 0 queries in queue 1 read views open inside InnoDB Main thread id 2992, state: flushing buffer pool pages Number of rows inserted 794294, updated 89203, deleted 13698, read 1453084305 0.00 inserts/s, 0.00 updates/s, 0.00 deletes/s, 0.00 reads/s ---------------------------- END OF INNODB MONITOR OUTPUT ============================ Thanks

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• Creating/renaming folder in Windows 7x64 extremely slow

  - by Newtopian

  Hi I have this very annoying problem : Whenever I want to create or edit a folder on my system it takes a very long time to complete. Right click-new folder... wait... wait... wait a good 30-60 seconds then type name and enter... wait again 30-60 seconds and then you can enter it. Browsing is normal and I have no problem creating folders through applications like eclipse but through explorer it is a real pain. Renaming folders has similar effect. otherwise the computer is (almost) normal, any ideas ?

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• SQL SERVER – Delay Command in SQL Server – SQL in Sixty Seconds #055

  - by Pinal Dave

  Have you ever needed WAIT or DELAY function in SQL Server?  Well, I personally have never needed it but I see lots of people asking for the same. It seems the need of the function is when developers are working with asynchronous applications or programs. When they are working with an application where user have to wait for a while for another application to complete the processing. If you are programming language developer, it is very easy for you to make the application wait for command however, in SQL I personally have rarely used this feature.  However, I have seen lots of developers asking for this feature in SQL Server, hence I have decided to build this quick video on the same subject. We can use WAITFOR DELAY ‘timepart‘ to create a SQL Statement to wait. Let us see the same concept in following SQL in Sixty Seconds Video: Related Tips in SQL in Sixty Seconds: Delay Function – WAITFOR clause – Delay Execution of Commands What would you like to see in the next SQL in Sixty Seconds video? Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: Database, Pinal Dave, PostADay, SQL, SQL Authority, SQL in Sixty Seconds, SQL Interview Questions and Answers, SQL Query, SQL Scripts, SQL Server, SQL Tips and Tricks, T SQL, Technology, Video Tagged: Identity

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• Thread Synchronization and Synchronization Primitives

  When considering synchronization in an application, the decision truly depends on what the application and its worker threads are going to do. I would use synchronization if two or more threads could possibly manipulate the same instance of an object at the same time. An example of this in C# can be demonstrated through the use of storing data in a static object. A static object is initialized once per application and the data within the object can be accessed by all threads. I would use the synchronization primitives to prevent any data from being manipulated by multiple threads simultaneously. This would reduce any data corruption from occurring within the object. On the other hand if all the threads used non static objects and were independent of the other tasks there would be no need to use synchronization. Synchronization Primitives in C#: Basic Blocking Locking Signaling Non-Blocking Synchronization Constructs The Basic Blocking methods include Sleep, Join, and Task.Wait.  These methods force threads to wait until other threads have completed. In addition, these methods can also force a thread to wait a set amount of time before continuing to work.   The Locking primitive prevents a thread from entering a critical section of code while another thread is in the same critical section.  If another thread attempts to enter a locked code, it will wait, until the code block is released. The Signaling primitive allows a thread to temporarily pause work until receiving a notification from another thread that it is ok to continue working. The Signaling primitive removes the need for polling.The Non-Blocking Synchronization Constructs protect access to a common field by calling upon processor primitives.

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• Commit in SQL

  - by PRajkumar

  SQL Transaction Control Language Commands (TCL)                                           (COMMIT) Commit Transaction As a SQL language we use transaction control language very frequently. Committing a transaction means making permanent the changes performed by the SQL statements within the transaction. A transaction is a sequence of SQL statements that Oracle Database treats as a single unit. This statement also erases all save points in the transaction and releases transaction locks. Oracle Database issues an implicit COMMIT before and after any data definition language (DDL) statement. Oracle recommends that you explicitly end every transaction in your application programs with a COMMIT or ROLLBACK statement, including the last transaction, before disconnecting from Oracle Database. If you do not explicitly commit the transaction and the program terminates abnormally, then the last uncommitted transaction is automatically rolled back.   Until you commit a transaction: ·         You can see any changes you have made during the transaction by querying the modified tables, but other users cannot see the changes. After you commit the transaction, the changes are visible to other users' statements that execute after the commit ·         You can roll back (undo) any changes made during the transaction with the ROLLBACK statement   Note: Most of the people think that when we type commit data or changes of what you have made has been written to data files, but this is wrong when you type commit it means that you are saying that your job has been completed and respective verification will be done by oracle engine that means it checks whether your transaction achieved consistency when it finds ok it sends a commit message to the user from log buffer but not from data buffer, so after writing data in log buffer it insists data buffer to write data in to data files, this is how it works.   Before a transaction that modifies data is committed, the following has occurred: ·         Oracle has generated undo information. The undo information contains the old data values changed by the SQL statements of the transaction ·         Oracle has generated redo log entries in the redo log buffer of the System Global Area (SGA). The redo log record contains the change to the data block and the change to the rollback block. These changes may go to disk before a transaction is committed ·         The changes have been made to the database buffers of the SGA. These changes may go to disk before a transaction is committed   Note:   The data changes for a committed transaction, stored in the database buffers of the SGA, are not necessarily written immediately to the data files by the database writer (DBWn) background process. This writing takes place when it is most efficient for the database to do so. It can happen before the transaction commits or, alternatively, it can happen some times after the transaction commits.   When a transaction is committed, the following occurs: 1.      The internal transaction table for the associated undo table space records that the transaction has committed, and the corresponding unique system change number (SCN) of the transaction is assigned and recorded in the table 2.      The log writer process (LGWR) writes redo log entries in the SGA's redo log buffers to the redo log file. It also writes the transaction's SCN to the redo log file. This atomic event constitutes the commit of the transaction 3.      Oracle releases locks held on rows and tables 4.      Oracle marks the transaction complete   Note:   The default behavior is for LGWR to write redo to the online redo log files synchronously and for transactions to wait for the redo to go to disk before returning a commit to the user. However, for lower transaction commit latency application developers can specify that redo be written asynchronously and that transaction do not need to wait for the redo to be on disk.   The syntax of Commit Statement is   COMMIT [WORK] [COMMENT ‘your comment’]; ·         WORK is optional. The WORK keyword is supported for compliance with standard SQL. The statements COMMIT and COMMIT WORK are equivalent. Examples Committing an Insert INSERT INTO table_name VALUES (val1, val2); COMMIT WORK; ·         COMMENT Comment is also optional. This clause is supported for backward compatibility. Oracle recommends that you used named transactions instead of commit comments. Specify a comment to be associated with the current transaction. The 'text' is a quoted literal of up to 255 bytes that Oracle Database stores in the data dictionary view DBA_2PC_PENDING along with the transaction ID if a distributed transaction becomes in doubt. This comment can help you diagnose the failure of a distributed transaction. Examples The following statement commits the current transaction and associates a comment with it: COMMIT     COMMENT 'In-doubt transaction Code 36, Call (415) 555-2637'; ·         WRITE Clause Use this clause to specify the priority with which the redo information generated by the commit operation is written to the redo log. This clause can improve performance by reducing latency, thus eliminating the wait for an I/O to the redo log. Use this clause to improve response time in environments with stringent response time requirements where the following conditions apply: The volume of update transactions is large, requiring that the redo log be written to disk frequently. The application can tolerate the loss of an asynchronously committed transaction. The latency contributed by waiting for the redo log write to occur contributes significantly to overall response time. You can specify the WAIT | NOWAIT and IMMEDIATE | BATCH clauses in any order. Examples To commit the same insert operation and instruct the database to buffer the change to the redo log, without initiating disk I/O, use the following COMMIT statement: COMMIT WRITE BATCH; Note: If you omit this clause, then the behavior of the commit operation is controlled by the COMMIT_WRITE initialization parameter, if it has been set. The default value of the parameter is the same as the default for this clause. Therefore, if the parameter has not been set and you omit this clause, then commit records are written to disk before control is returned to the user. WAIT | NOWAIT Use these clauses to specify when control returns to the user. The WAIT parameter ensures that the commit will return only after the corresponding redo is persistent in the online redo log. Whether in BATCH or IMMEDIATE mode, when the client receives a successful return from this COMMIT statement, the transaction has been committed to durable media. A crash occurring after a successful write to the log can prevent the success message from returning to the client. In this case the client cannot tell whether or not the transaction committed. The NOWAIT parameter causes the commit to return to the client whether or not the write to the redo log has completed. This behavior can increase transaction throughput. With the WAIT parameter, if the commit message is received, then you can be sure that no data has been lost. Caution: With NOWAIT, a crash occurring after the commit message is received, but before the redo log record(s) are written, can falsely indicate to a transaction that its changes are persistent. If you omit this clause, then the transaction commits with the WAIT behavior. IMMEDIATE | BATCH Use these clauses to specify when the redo is written to the log. The IMMEDIATE parameter causes the log writer process (LGWR) to write the transaction's redo information to the log. This operation option forces a disk I/O, so it can reduce transaction throughput. The BATCH parameter causes the redo to be buffered to the redo log, along with other concurrently executing transactions. When sufficient redo information is collected, a disk write of the redo log is initiated. This behavior is called "group commit", as redo for multiple transactions is written to the log in a single I/O operation. If you omit this clause, then the transaction commits with the IMMEDIATE behavior. ·         FORCE Clause Use this clause to manually commit an in-doubt distributed transaction or a corrupt transaction. ·         In a distributed database system, the FORCE string [, integer] clause lets you manually commit an in-doubt distributed transaction. The transaction is identified by the 'string' containing its local or global transaction ID. To find the IDs of such transactions, query the data dictionary view DBA_2PC_PENDING. You can use integer to specifically assign the transaction a system change number (SCN). If you omit integer, then the transaction is committed using the current SCN. ·         The FORCE CORRUPT_XID 'string' clause lets you manually commit a single corrupt transaction, where string is the ID of the corrupt transaction. Query the V$CORRUPT_XID_LIST data dictionary view to find the transaction IDs of corrupt transactions. You must have DBA privileges to view the V$CORRUPT_XID_LIST and to specify this clause. ·         Specify FORCE CORRUPT_XID_ALL to manually commit all corrupt transactions. You must have DBA privileges to specify this clause. Examples Forcing an in doubt transaction. Example The following statement manually commits a hypothetical in-doubt distributed transaction. Query the V$CORRUPT_XID_LIST data dictionary view to find the transaction IDs of corrupt transactions. You must have DBA privileges to view the V$CORRUPT_XID_LIST and to issue this statement. COMMIT FORCE '22.57.53';

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• c# scripting execution with xna (actions take more than 1 frame)

  - by user658091

  I'm trying to figure out how to implement c# scripting into my game (XNA with C#). I will be using C# as the scripting language. My question is, how to call functions that take more than 1 frame to finish? For example: class UserScript : Script { public override void execute(Game game) { //script must wait for dialog to be closed game.openDialog("This is a dialog"); //script should'nt wait for this int goldToGive = 100; goldToGive += 100; game.addGold(goldToGive); // //script should wait for cinematic to end game.startCinematic("name_of_cinematic"); //doesn't wait game.addGold(100); } } I found that you can do that with yield, but I'm not sure if it's the correct way (It's from 2010, the article mentioned no longer exists). http://stackoverflow.com/questions/3540231/implementing-a-simple-xml-based-scripting-language-for-an-xna-game Is yield the answer? If so, can anyone point me any examples/tutorials/books? I haven't found any regarding my situation. If not, what approach should I take? or am I better off with multi-threading?

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• SQL SERVER – Finding Latch Statistics

  - by pinaldave

  Last month I wrote SQL Server Wait Types and Queues series SQL SERVER – Summary of Month – Wait Type – Day 28 of 28. I had great fun to write the series. I learned a lot and I felt this has created some deep interest on the subject with others. I recently received very interesting question from one of the reader after reading SQL SERVER – PAGELATCH_DT, PAGELATCH_EX, PAGELATCH_KP, PAGELATCH_SH, PAGELATCH_UP – Wait Type – Day 12 of 28 that if they can know what kind of latches are waiting and what is their count. Absolutely! SQL Server team has already provided DMV which does the same. -- Latch SELECT * FROM sys.dm_os_latch_stats ORDER BY wait_time_ms DESC Above script will return you details about how many latches were waiting for how long. After going over this script I feel like going deep into the subject further. I will post a blog post on the subject soon. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: PostADay, SQL, SQL Authority, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology

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• Is true multithreading really necessary?

  - by Jonathan Graef

  So yeah, I'm creating a programming language. And the language allows multiple threads. But, all threads are synchronized with a global interpreter lock, which means only one thread is allowed to execute at a time. The only way to get the threads to switch off is to explicitly tell the current thread to wait, which allows another thread to execute. Parallel processing is of course possible by spawning multiple processes, but the variables and objects in one process cannot be accessed from another. However the language does have a fairly efficient IPC interface for communicating between processes. My question is: Would there ever be a reason to have multiple, unsynchronized threads within a single process (thus circumventing the GIL)? Why not just put thread.wait() statements in key positions in the program logic (presuming thread.wait() isn't a CPU hog, of course)? I understand that certain other languages that use a GIL have processor scheduling issues (cough Python), but they have all been resolved.

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• Google App Engine - Figure out the time the current request reached the app engine

  - by Spines

  Is there a way I can figure out the time the current request reached the app engine? For example a user might make a request to my app, but due to app engine latencies my code might not start handling the request until one second later, is there a way I can figure out that the user has already had to wait one second? The reason I want to know how to do this is because I want to do different things based on if the user already had to wait. If the user already had to wait a significant amount of time I will just serve them a page out of the cache, if the user hasn't had to wait yet then I will serve them a page which takes a while to render.

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• What is the right pattern for a async data fetching method in .net async/await

  - by s093294

  Given a class with a method GetData. A few other clients call GetData, and instead of it fetching data each time, i would like to create a pattern where the first call starts the task to get the data, and the rest of the calls wait for the task to complete. private Task<string> _data; private async Task<string> _getdata() { return "my random data from the net"; //get_data_from_net() } public string GetData() { if(_data==null) _data=_getdata(); _data.wait(); //are there not a problem here. cant wait a task that is already completed ? if(_data.status != rantocompletion) _data.wait() is not any better, it might complete between the check and the _data.wait? return _data.Result; } How would i do the pattern correctly? (Solution) private static object _servertime_lock = new object(); private static Task<string> _servertime; private static async Task<string> servertime() { try { var thetvdb = new HttpClient(); thetvdb.Timeout = TimeSpan.FromSeconds(5); // var st = await thetvdb.GetStreamAsync("http://www.thetvdb.com/api/Updates.php?type=none"); var response = await thetvdb.GetAsync("http://www.thetvdb.com/api/Updates.php?type=none"); response.EnsureSuccessStatusCode(); Stream stream = await response.Content.ReadAsStreamAsync(); XDocument xdoc = XDocument.Load(stream); return xdoc.Descendants("Time").First().Value; } catch { return null; } } public static async Task<string> GetServerTime() { lock (_servertime_lock) { if (_servertime == null) _servertime = servertime(); } var time = await _servertime; if (time == null) _servertime = null; return time; }

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• javascript mouse cursor change on page load in firefox browser 3.5

  - by Amit

  Hi in case of full page submit a trasparent div id coming and changing the cursor to 'wait' . Now when the page is getting submitted and new page is coming up cursor still remains to 'wait' not changing to default until mouse is moved in Firefox Here is simple html click on show button div is coming when user move mouse over the div cursor is changing as wait cursor. Now when this page is loaded again pressing F5 cursor remain as wait cursor in firefox its working fine in IE is there any way to make the cursor as default on pageload in Firefox <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" /> <title>Untitled Document</title> <style> body{ cursor:default; } </style> <script src="js/jquery.js"> </script> <script> var test = true; $(document).ready(function(){ $('#maindiv').css('display','none') }); function showDiv(){ $('#maindiv').css('display','block') } </script> </head> <body> <div id="divBody" style="background-color:red;width:500px;height:500px" >aa <div id="maindiv" style="background-color:#999999;height:100$;width:400px;height:400px;cursor:wait"> sss </div>aa </div> <input type="button" value="show" onclick="showDiv()"/> </body> </html>

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• Problem Executing Async Web Request

  - by davidhayes

  Hi Can anyone tell me what I've done wrong with this simple code? When I run it it hangs on using (Stream postStream = request.EndGetRequestStream(asynchronousResult)) If I comment out the requestState.Wait.WaitOne(); line the code executes correctly but obviously doesn't wait for the response. I'm guessing the the call to EndGetRequestStream is somehow returning me to the context of the main thread?? I'm pretty sure my code is essentially the same as the sample though (MSDN Documentation) using System; using System.Net; using System.Windows; using System.Windows.Controls; using System.Windows.Documents; using System.Windows.Ink; using System.Windows.Input; using System.Windows.Media; using System.Windows.Media.Animation; using System.Windows.Shapes; using System.IO; using System.Text; namespace SBRemoteClient { public class JSONClient { public string ExecuteJSONQuery(string url, string query) { System.Uri uri = new Uri(url); HttpWebRequest request = (HttpWebRequest)WebRequest.Create(uri); request.Method = "POST"; request.Accept = "application/json"; byte[] requestBytes = Encoding.UTF8.GetBytes(query); RequestState requestState = new RequestState(request, requestBytes); IAsyncResult resultRequest = request.BeginGetRequestStream(new AsyncCallback(GetRequestStreamCallback), requestState); requestState.Wait.WaitOne(); IAsyncResult resultResponse = (IAsyncResult)request.BeginGetResponse(new AsyncCallback(GetResponseStreamCallback), requestState); requestState.Wait.WaitOne(); return requestState.Response; } private static void GetRequestStreamCallback(IAsyncResult asynchronousResult) { try { RequestState requestState = (RequestState)asynchronousResult.AsyncState; HttpWebRequest request = requestState.Request; using (Stream postStream = request.EndGetRequestStream(asynchronousResult)) { postStream.Write(requestState.RequestBytes, 0, requestState.RequestBytes.Length); } requestState.Wait.Set(); } catch (Exception e) { Console.Out.WriteLine(e); } } private static void GetResponseStreamCallback(IAsyncResult asynchronousResult) { RequestState requestState = (RequestState)asynchronousResult.AsyncState; HttpWebRequest request = requestState.Request; using (HttpWebResponse response = (HttpWebResponse)request.EndGetResponse(asynchronousResult)) { using (Stream responseStream = response.GetResponseStream()) { using (StreamReader streamRead = new StreamReader(responseStream)) { requestState.Response = streamRead.ReadToEnd(); requestState.Wait.Set(); } } } } } }

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• IE7 crashed when RemoveDialogHandler is called

  - by Baptiste Pernet

  I have this code: FileDownloadHandler handler = new FileDownloadHandler(fileName); Browser.AddDialogHandler(handler); //using (new UseDialogOnce(Browser.DialogWatcher, handler)) //{ Browser.Button(Find.ById("ButtonExportReport")).ClickNoWait(); handler.WaitUntilFileDownloadDialogIsHandled(20); handler.WaitUntilDownloadCompleted(30); //} Browser.RemoveDialogHandler(handler); And when I call Browser.RemoveDialogHandler, Internet Explorer 7 crashes with the message: "no installed debugger has just_in-time debugging enabled" (I don't know how to debug IE7 because I only have the CLR debugger which can debug only managed code) Do you know what I should do ? Any path where I should look for information ? Thanks EDIT: In fact the error is not cause by the .RemoveDialogHandler I added ZvLogManager.Info("start wait"); Browser.Wait(10); ZvLogManager.Info("end wait"); just before the .RemoveDialogHandler, and I get the error message of IE between the "start wait" and "end wait". So it the download of the file that makes it crash. Any idea ?

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• Concurrent Threads in C# using BackgroundWorker

  - by Jim Fell

  My C# application is such that a background worker is being used to wait for the acknowledgement of some transmitted data. Here is some psuedo code demonstrating what I'm trying to do: UI_thread { TransmitData() { // load data for tx // fire off TX background worker } RxSerialData() { // if received data is ack, set ack received flag } } TX_thread { // transmit data // set ack wait timeout // fire off ACK background worker // wait for ACK background worker to complete // evaluate status of ACK background worker as completed, failed, etc. } ACK_thread { // wait for ack received flag to be set } What happens is that the ACK BackgroundWorker times out, and the acknowledgement is never received. I'm fairly certain that it is being transmitted by the remote device because that device has not changed at all, and the C# application is transmitting. I have changed the ack thread from this (when it was working)... for( i = 0; (i < waitTimeoutVar) && (!bAckRxd); i++ ) { System.Threading.Thread.Sleep(1); } ...to this... DateTime dtThen = DateTime.Now(); DateTime dtNow; TimeSpan stTime; do { dtNow = DateTime.Now(); stTime = dtNow - dtThen; } while ( (stTime.TotalMilliseconds < waitTimeoutVar) && (!bAckRxd) ); The latter generates a very acurate wait time, as compared to the former. However, I am wondering if removal of the Sleep function is interferring with the ability to receive serial data. Does C# only allow one thread to run at a time, that is, do I have to put threads to sleep at some time to allow other threads to run? Any thoughts or suggestions you may have would be appreciated. I am using Microsoft Visual C# 2008 Express Edition. Thanks.

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• Executing sc.exe from .NET Process unable to start and stop service.

  - by Jason

  I'm trying to restart the service from a remote machine. Here is my code. The problem is that I need to enter startinfo.filename = "sc.exe" since I'm putting "start /wait sc" this is causing an error. Here is my code, any thoughts. Also if anyone has any idea how to keep the cmd window open after this is ran so I could see the code that was ran that would be awesome. string strCommandStop1; string strCommandStop2; string strCommandStart1; string strCommandStart2; string strServer = "\\" + txtServerName.Text; string strDb1 = "SqlAgent$" + txtInsName.Text; string strDb2 = "MSSQL$" + txtInsName.Text; strCommandStop1 = @"start /wait sc " + strServer + " Stop " + strDb1; strCommandStop2 = @"start /wait sc " + strServer + " Stop " + strDb2; strCommandStart1 = @"start /wait sc " + strServer + " Start " + strDb2; strCommandStart2 = @"start /wait sc " + strServer + " Start " + strDb1; try { ProcessStartInfo startInfo = new ProcessStartInfo(); startInfo.CreateNoWindow = true; startInfo.Arguments = strCommandStop1; startInfo.Arguments = strCommandStop2; startInfo.Arguments = strCommandStart1; startInfo.Arguments = strCommandStart2; startInfo .FileName = "sc.exe"; Process.Start(startInfo); } catch (Exception e) { MessageBox.Show(e.Message); }

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• Is it possible to create a throttle function that can take in as parameters another function (that also has parameters), and the time delay

  - by Stan Quinn

  So I've already written a function that works (based on underscores throttle) for functions that don't take in a parameter, but I'd like to make it generic enough to pass in a function with a variable number of parameters. Here's what I have: (function () { var lastTime = new Date().getTime(); function foo() { var newTime = new Date().getTime(); var gap = newTime - lastTime; // Travels up scope chain to use parents lastTime. Function has access to variables declared in the same scope console.log('foo called, gap:' + gap); lastTime = newTime; // Updates lastTime //console.log(x); //x++; } var throttle = function(func, wait) { var result; var timeout = null; // flag updated through closure var previous = 0; // time last run updated through closure return function() { //func, wait, timeout, previous available through scope var now = new Date().getTime(); var remaining = wait - (now - previous); if (remaining <= 0) { clearTimeout(timeout); timeout = null; previous = now; result = func.apply(this, arguments); //func is available through closure } return result; }; }; document.addEventListener("scroll", throttle(foo, 1000)); //document.addEventListener("scroll", throttle(foo(5), 2000)); }()); But I'd like to modify foo to foo(x) and get this to work (function () { var lastTime = new Date().getTime(); function foo(x) { var newTime = new Date().getTime(); var gap = newTime - lastTime; // Travels up scope chain to use parents lastTime. Function has access to variables declared in the same scope console.log('foo called, gap:' + gap); lastTime = newTime; // Updates lastTime console.log(x); x++; } var throttle = function(func, wait) { var result; var timeout = null; // flag updated through closure var previous = 0; // time last run updated through closure return function() { //func, wait, timeout, previous available through scope var now = new Date().getTime(); var remaining = wait - (now - previous); if (remaining <= 0) { clearTimeout(timeout); timeout = null; previous = now; result = func.apply(this, arguments); //func is available through closure } return result; }; }; document.addEventListener("scroll", throttle(foo(5), 2000)); }());

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• Win32 reset event like synchronization class with boost C++

  - by fgungor

  I need some mechanism reminiscent of Win32 reset events that I can check via functions having the same semantics with WaitForSingleObject() and WaitForMultipleObjects() (Only need the ..SingleObject() version for the moment) . But I am targeting multiple platforms so all I have is boost::threads (AFAIK) . I came up with the following class and wanted to ask about the potential problems and whether it is up to the task or not. Thanks in advance. class reset_event { bool flag, auto_reset; boost::condition_variable cond_var; boost::mutex mx_flag; public: reset_event(bool _auto_reset = false) : flag(false), auto_reset(_auto_reset) { } void wait() { boost::unique_lock<boost::mutex> LOCK(mx_flag); if (flag) return; cond_var.wait(LOCK); if (auto_reset) flag = false; } bool wait(const boost::posix_time::time_duration& dur) { boost::unique_lock<boost::mutex> LOCK(mx_flag); bool ret = cond_var.timed_wait(LOCK, dur) || flag; if (auto_reset && ret) flag = false; return ret; } void set() { boost::lock_guard<boost::mutex> LOCK(mx_flag); flag = true; cond_var.notify_all(); } void reset() { boost::lock_guard<boost::mutex> LOCK(mx_flag); flag = false; } }; Example usage; reset_event terminate_thread; void fn_thread() { while(!terminate_thread.wait(boost::posix_time::milliseconds(10))) { std::cout << "working..." << std::endl; boost::this_thread::sleep(boost::posix_time::milliseconds(1000)); } std::cout << "thread terminated" << std::endl; } int main() { boost::thread worker(fn_thread); boost::this_thread::sleep(boost::posix_time::seconds(1)); terminate_thread.set(); worker.join(); return 0; } EDIT I have fixed the code according to Michael Burr's suggestions. My "very simple" tests indicate no problems. class reset_event { bool flag, auto_reset; boost::condition_variable cond_var; boost::mutex mx_flag; public: explicit reset_event(bool _auto_reset = false) : flag(false), auto_reset(_auto_reset) { } void wait() { boost::unique_lock<boost::mutex> LOCK(mx_flag); if (flag) { if (auto_reset) flag = false; return; } do { cond_var.wait(LOCK); } while(!flag); if (auto_reset) flag = false; } bool wait(const boost::posix_time::time_duration& dur) { boost::unique_lock<boost::mutex> LOCK(mx_flag); if (flag) { if (auto_reset) flag = false; return true; } bool ret = cond_var.timed_wait(LOCK, dur); if (ret && flag) { if (auto_reset) flag = false; return true; } return false; } void set() { boost::lock_guard<boost::mutex> LOCK(mx_flag); flag = true; cond_var.notify_all(); } void reset() { boost::lock_guard<boost::mutex> LOCK(mx_flag); flag = false; } };

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