semaphore | 易学教程

Difference between Semaphore and Condition (ReentrantLock)

阅读更多关于 Difference between Semaphore and Condition (ReentrantLock)

问题 Does anyone know the differences between the methods acquire () and release () ( java.util.concurrent.Semaphore ) and await () and signal (new ReentrantLock().newCondition() ) . Can you expose a pseudo code for each of these methods? 回答1: Superficially the behavior of these method might look similar - acquire()/await() can make threads block in some cirsumstances and release()/signal() can unblock threads in some circumstances. However Semaphore and Condition serve different purposes: java

Java并发之CountDownLatch、CyclicBarrier、Semaphore使用实例

阅读更多关于 Java并发之CountDownLatch、CyclicBarrier、Semaphore使用实例

最近学习了Java并发编程中的CountDownLatch、CyclicBarrier、Semaphore，做个小总结。这三个类都是java1.5中提供的一些非常有用的辅助类，用于帮助程序员实现并发编程。 CountDownLatch 背景 CountDownLatch是一个同步工具类，用来协调多个线程之间的同步，或者说起到线程之间的通信（而不是用作互斥的作用）。 CountDownLatch能够使一个线程在等待另外一些线程完成各自工作之后，再继续执行。使用一个计数器进行实现。计数器初始值为线程的数量。当每一个线程完成自己任务后，计数器的值就会减一。当计数器的值为0时，表示所有的线程都已经完成一些任务，然后在CountDownLatch上等待的线程就可以恢复执行接下来的任务。 countDownLatch是在java1.5被引入，跟它一起被引入的工具类还有CyclicBarrier、Semaphore、concurrentHashMap和BlockingQueue。存在于java.util.cucurrent包下。概念 countDownLatch这个类使一个线程等待其他线程各自执行完毕后再执行。是通过一个计数器来实现的，计数器的初始值是线程的数量。每当一个线程执行完毕后，计数器的值就-1，当计数器的值为0时，表示所有线程都执行完毕，然后在闭锁上等待的线程就可以恢复工作了。

Ubuntu Semaphore: Segmentation fault (core dumped)

阅读更多关于 Ubuntu Semaphore: Segmentation fault (core dumped)

问题 I am learning semaphores in C using Ubuntu right now. The professor just throw us this code and ask us to study it and observe. When I compiled I get a warning that ctime(&sem_buf.sem_ctime) returns an int , not a char * but nothing major. When I run it the output is just: Semaphore identifier: 0 Segmentation fault (core dumped) . I am very confused as of what went wrong and I have no idea what is going on in this code. Some help would be very much appreciated. Here is the code: #include <sys

Ubuntu Semaphore: Segmentation fault (core dumped)

阅读更多关于 Ubuntu Semaphore: Segmentation fault (core dumped)

Semaphore实现原理

阅读更多关于 Semaphore实现原理

示例代码 public class TestSemaphore { public static Semaphore semaphore = new Semaphore ( 2 ) ; public static void main ( String [ ] args ) { System . out . println ( "main start" ) ; for ( int i = 0 ; i < 5 ; i ++ ) { new Thread ( new Taskes ( ) ) . start ( ) ; } System . out . println ( "main end" ) ; } } class Taskes implements Runnable { @Override public void run ( ) { try { TestSemaphore . semaphore . acquire ( ) ; LocalTime time = LocalTime . now ( ) ; System . out . println ( Thread . currentThread ( ) . getName ( ) + "任务开始--------" + time . getMinute ( ) + ":" + time . getSecond ( ) ) ;

better way to interrupt my python code when subprocess is running?

阅读更多关于 better way to interrupt my python code when subprocess is running?

问题 I recently answered a question here The question was: how to interrupt a python script when a subprocess is running (possibly windows-specific). I suggested to create a thread to run the subprocess on, and wait on the mainloop for CTRL+C / KeyboardInterrupt exception so the child process can be killed. It works, but bit of a hack because I did this: Basically, I make a non-cpu active (but polling) loop which waits 100ms then checks for the shared boolean done . If the subprocess exits, the

Critical Section in JavaScript or jQuery

阅读更多关于 Critical Section in JavaScript or jQuery

问题 I have a webpage, in which a certain Ajax event is triggered asynchronously. This Ajax section could be called once or more than once. I do not have control over the number of times this event is triggered, nor the timing. Also, there is a certain code in that Ajax section that should run as a critical section, meaning, when it is running, no other copy of that code should be running. Here is a pseudo code: Run JavaScript or jQuery code Enter critical section that is Ajax (when a certain

How can semaphores implemented on multi-core systems?

阅读更多关于 How can semaphores implemented on multi-core systems?

问题 I can not understand how Posix allows any thread to unlock (post) on a semaphore. Let's consider following example: // sem1 and sem2 are a Posix semaphore, // properly initialized for single process use // at this point, sem2 is locked, sem1 is unlocked // x and y are global (non-atomic, non-volatile) integer variables // thread 1 - is executing right now rc = sem_wait(&sem1); // succeeded, semaphore is 0 now x = 42; y = 142; sem_post(&sem2); while (true); // thread 2. waits for sem2 to be

多线程（二）

阅读更多关于多线程（二）

简易阻止：Sleep,阻止给定的时间周期；Join,等待另一个线程完成。一旦被阻止，线程立刻放弃分配给他的CPU资源，并且ThreadState属性值改为WaitSleepJoin。停止阻止的方式：(1)操作超时（2）通过Thread的Interrupt中断了（3）通过Thread的Abort放弃了. Thread.Sleep(Timeout.Infinite);//休眠直到中断 Thread.Sleep(TimeSpan.FromSeconds(1));//休眠一秒 Thread.Sleep(0);//暂时的放弃CPU,时间刚刚够其他时间片里的线程执行。 Join方法也接收一个使用毫秒或用TimeSpan类的超时参数，当Join超时时返回false，如果线程已终止，则返回true。（在阻止是Join保持信息汲取，sleep停止信息汲取）。锁系统：lock,确保只有一个线程访问某资源，不能跨进程，速度快； Mutex, ,确保只有一个线程访问某资源，可以跨进程，速度中等； Semaphore,不超过制定数目的线程访问某资源，可以跨进程，速度中等。任何对所有有关系的线程都可见的对象都可以作为同步对象，但要服从一个硬性规定：它必须是引用类型。也强烈建议同步对象最好私有在类里面（比如一个私有实例字段）防止无意间从外部锁定相同的对象。服从这些规则，同步对象可以兼对象和保护两种作用。

进程通信之IPC通信对象——信号灯

阅读更多关于进程通信之IPC通信对象——信号灯

进程间通过信号灯的通信。信号灯的创建函数semget()：信号灯的删除函数semctl(): 例子1：信号灯的创建和删除，通过semget函数创建，调用semctl函数删除。 #include"sys/types.h" #include"signal.h" #include"unistd.h" #include"stdio.h" #include"stdlib.h" #include"sys/sem.h" int main() { int semid; semid=semget(IPC_PRIVATE,3,0777); if(semid<0) { printf("creat semaphore failure\n"); return -1; } printf("creat semaphore success\n"); system("ipcs -s"); //delete semaphore semctl(semid,0,IPC_RMID,NULL); system("ipcs -s"); return 0; } 运行结果如图：成功创建3个信号灯后，又成功删除了。例子2：一般我们可以用全局变量来实现父子线程之间的同步，如下thread.c的内容：通过定义一个全局变量thread_inter来实现父子线程的同步问题。 #include<pthread.h> #include

订阅 semaphore