semaphore | 易学教程

Do I need to Dispose a SemaphoreSlim

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问题 According to the documentation: "a SemaphoreSlim doesn't use a Windows kernel semaphore". Are there any special resources used by the SemaphoreSlim which make it important to call Dispose when the SemaphoreSlim will no longer be used? 回答1: Yes. It may use a ManualResetEvent that uses a SafeWaitHandle which is a SafeHandle and it has an unmanaged handle. You can see it in the reference source here. SafeHandle is finalizable so if you don't dispose of it (by disposing of the SemaphoreSlim ) it

spinlock与linux内核调度的关系

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作者：刘洪涛，华清远见嵌入式学院高级讲师，ARM公司授权ATC讲师。关于自旋锁用法介绍的文章，已经有很多，但有些细节的地方点的还不够透。我这里就把我个人认为大家容易有疑问的地方拿出来讨论一下。一、自旋锁（spinlock）简介自旋锁在同一时刻只能被最多一个内核任务持有，所以一个时刻只有一个线程允许存在于临界区中。这点可以应用在多处理机器、或运行在单处理器上的抢占式内核中需要的锁定服务。二、信号量简介这里也介绍下信号量的概念，因为它的用法和自旋锁有相似的地方。 Linux中的信号量是一种睡眠锁。如果有一个任务试图获得一个已被持有的信号量时，信号量会将其推入等待队列，然后让其睡眠。这时处理器获得自由去执行其它代码。当持有信号量的进程将信号量释放后，在等待队列中的一个任务将被唤醒，从而便可以获得这个信号量。三、自旋锁和信号量对比在很多地方自旋锁和信号量可以选择任何一个使用，但也有一些地方只能选择某一种。下面对比一些两者的用法。表1-1自旋锁和信号量对比应用场合信号量or 自旋锁低开销加锁（临界区执行时间较快）优先选择自旋锁低开销加锁（临界区执行时间较长）优先选择信号量临界区可能包含引起睡眠的代码不能选自旋锁，可以选择信号量临界区位于非进程上下文时，此时不能睡眠优先选择自旋锁，即使选择信号量也只能用 down_trylock 非阻塞的方式

How can I get multiple calls to sem_open working in C?

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问题 I'm experiencing a lot of difficulty getting Semaphores to work on a Linux based system in C. The process of my application is such: Application starts Application forks into child/parent Each process uses sem_open with a common name to open the semaphore. If I create the semaphore before forking, it works fine. However, requirements prevent me from doing so. When I try to call sem_open for the second time, I get a "Permission Denied" error (via errno ). Is it possible to do this in any way?

Abandoned named semaphore not released

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问题 when a C# program holds a named semaphore, it does not seem to be released when the application is terminated early (for example by pressing Ctrl+C or closing the console window). At least not until all instances of the process have terminated. With a named mutex an AbandonedMutexException is raised in this case but not with a semaphore. How do you prevent one program instance from stalling when another program instance has been terminated early? class Program { // Same with count > 1 private

Signalling to a parent process that a child process is fully initialised

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问题 I'm launching a child process that exposes a WCF endpoint. How can I signal from the child process to the parent process that the child is fully initialised and that it can now access the endpoint? I'd thought about using Semaphores for this purpose but can't quite figure out how to achieve the required signal. string pipeUri = "net.pipe://localhost/Node0"; ProcessStartInfo startInfo = new ProcessStartInfo("Node.exe", "-uri=" + pipeUri); Process p = Process.Start(startInfo);

How can you implement a condition variable using semaphores?

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问题 A while back I was thinking about how to implement various synchronization primitives in terms of one another. For example, in pthreads you get mutexes and condition variables, and from these can build semaphores. In the Windows API (or at least, older versions of the Windows API) there are mutexes and semaphores, but no condition variables. I think that it should be possible to build condition variables out of mutexes and semaphores, but for the life of me I just can't think of a way to do

Need help in implementing the Producer-Consumer problem with pthread and semaphore

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问题 I am trying to implement the Producer and Consumer problem in C++ using pthread and semaphore. I have one Producer and two consumers. My producer reads a string from a file and stores it in a queue character by character. The consumers read from the string and store in a char character also one by one. The problem is that only one of my Consumer is reading from the queue, other is not and its array is remaining empty. How do I fix this problem. Here is my program: #include<iostream> #include

Semaphore Vs Condition Variables in multithreading?

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问题 Problem : I have to increment x1 and x2 variable which should be done by separate threads and next increment of both variables should not be called until previous increment of both variable is not completed. Problem: x1 = 0; x2 = 0; x1++; and x2++; should run parallel on different threads and wait for printing. should print: x1 = 1 and x2 = 1 x1++; and x2++; should run parallel on different threads and wait for printing. should print: x1 = 2 and x2 = 2 x1++; and x2++; should run parallel on

C# - Error propagation with ContinueWith

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问题 I'm a threading newbie and am trying to use SemaphoreSlim to allow me to run a set number of long tasks simultaneously. My challenge is that, given the way I've written it, any exceptions are not being captured correctly. Here's a very simplified example of my current code: public void ThreadTest() { try { var currentTasks = new List<Task>(); SemaphoreSlim maxThread = new SemaphoreSlim(2); for (int i = 1; i < 5; ++i) { maxThread.Wait(); var testTask = Faulty().ContinueWith(tsk => maxThread

Programming in UNIX - Semaphores,shared memory in C

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I started a week ago understanding and working with semaphores and shared memory, and actually created this program, the problem is i cant find anything wrong with it i been looking at it for hours and everything seems correct.. The code compiles and i can create the build but when i execute it nothing happens ... #include <stdio.h> #include <stdlib.h> #include <unistd.h> #include <sys/ipc.h> #include <sys/shm.h> #include <stdio.h> #include <sys/fcntl.h> #include <semaphore.h> #define MAXCHILDS 4 #define MAX_SIZE 10 #define MAX_WRITES 4 typedef struct{ int m[MAX_SIZE][MAX_SIZE]; } matrix; /