synchronization | 易学教程

pthread condition variables on Linux, odd behaviour

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问题 I'm synchronizing reader and writer processes on Linux. I have 0 or more process (the readers) that need to sleep until they are woken up, read a resource, go back to sleep and so on. Please note I don't know how many reader processes are up at any moment. I have one process (the writer) that writes on a resource, wakes up the readers and does its business until another resource is ready (in detail, I developed a no starve reader-writers solution, but that's not important). To implement the

In Java, how do I test if an object's monitor is locked? [duplicate]

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This question already has an answer here: How do determine if an object is locked (synchronized) so not to block in Java? 7 answers Java: How to check if a lock can be acquired? [duplicate] 3 answers In Java, how do I test if an object's monitor is locked? In other words, given a object obj, does any thread own obj's monitor? I do not care which thread owns the monitor. All I need to test is if ANY thread owns a given object's monitor. Since a thread other than the current thread could own the monitor, Thread.holdsLock( obj ) is not enough as it only checks the current thread. I am trying to

Mutex ownership queue order

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问题 Say, if I have three threads that all access the same mutually exclusive part via a mutex. Let me give you this example. The first thread probes the mutex and gets its ownership first: //THREAD 1 //TIME: 2013-03-13 01:00:00.000Z WaitForSingleObject(hMutex, INFINITE); //Performs the operation that lasts 50 ms ReleaseMutex(hMutex); Then 10 ms later the thread 2 also requests it: //THREAD 2 //TIME: 2013-03-13 01:00:00.010Z WaitForSingleObject(hMutex, INFINITE); //Do work ReleaseMutex(hMutex);

Can someone explain join method in Java Thread class?

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问题 public final synchronized void join(long millis) throwsInterruptedException { long base = System.currentTimeMillis(); long now = 0; if (millis < 0) { throw new IllegalArgumentException("timeout value is negative"); } if (millis == 0) { while (isAlive()) { wait(0); } } else { while (isAlive()) { long delay = millis - now; if (delay <= 0) { break; } wait(delay); now = System.currentTimeMillis() - base; } } } How does wait(0) make the main thread wait until it finishes. Thread is calling wait on

Threads access on Synchronized Block/Code Java

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I was reading Synchronized working. Here is the example: public class Singleton{ private static volatile Singleton _instance; public static Singleton getInstance(){ if(_instance == null){ synchronized(Singleton.class){ if(_instance == null) _instance = new Singleton(); } } return _instance; } Let Suppose two Thread A and B are accessing getInstance(); method, If thread A is in synchronized block then thread B will skip that block and execute next block/statement or will wait/blocked until Thread A leave the synchronized block. 2nd What is, why is Singleton.class in synchronized parameter and

function increment sync with video (or auto increment)

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I'm busy with a webdoc that I'm partially creating on hype , the video are hosted on vimeo (so I need to use the vimeo api for some tasks like seekto) but my difficulties should be limited to js. the objective is to display a given image at a given time interval of the video . With my code below, I do get the string "test", "success" and "confirmed success" at the right time in my div id=popimgbox, and I can seek back and forth in the video and still get the right "answear", if I may say so. Now, I have images that are all stored in the same folder, and all named popimgX.jpg, with X being a

Workflow to synchronise Mercurial repositories via email with bundles

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问题 I have two directories on two different computers - machine A (Windows) and machine B (OSX) - and I want to keep the two directories via Mercurial in sync. [*] The restriction is that the two machines are not connected via LAN/WAN; the only way to move data between them is via email . So I thought emailing Mercurial bundles as deltas could do the trick. My current workflow is roughly this (using a local tag lcb for the latest change bundle): Say I work on machine A . At the end of the day I

Alternative to Lock.tryLock() in Java 1.4

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I would like to know if there is an existing alternative or how to implement the semantics of java.util.concurrent.locks.Lock#tryLock() before Java 5. That is the possibility to back off immediately if the lock is already held by another thread. If you need a Lock supporting a tryLock operation, you can’t use the intrinsic locking facility of Java. You have to implement your own Lock class which maintains the required state, i.e. an owner Thread and a counter and might use the intrinsic locking for its implementation of the thread-safe updates and blocking (there are not much alternatives in

Aquire Singleton class Instance Multithread

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To get the instance of the class with Singleton pattern, I want use the following function: This is a sketch interface uses SyncObjs; type TMCriticalSection = class(TCriticalSection) private Dummy : array [0..95] of Byte; end; var InstanceNumber : Integer; AObject: TObject; CriticalSection: TMCriticalSection; function getInstance: TObject; implementation uses Windows; function getInstance: TObject; begin //I Want somehow use InterlockedCompareExchange instead of CriticalSession, for example if InterlockedCompareExchange(InstanceNumber, 1, 0) > 0 then begin Result := AObject; end else begin

Is there such a synchronization tool as “single-item-sized async task buffer”?

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问题 Many times in UI development I handle events in such a way that when an event first comes - I immediately start processing, but if there is one processing operation in progress - I wait for it to complete before I process another event. If more than one event occurs before the operation completes - I only process the most recent one. The way I typically do that my process method has a loop and in my event handler I check a field that indicates if I am currently processing something and if I