semaphore

JUC 回顾 1 NIO主要内容:Buffer、Channel 2 非阻塞式网络编程 今天任务 1 volatile的使用 2 原子变量和CAS算法 3 Lock接口 4 并发集合 5 同步工具类 第一节 JUC 概述 在 Java 5.0 提供了 java.util.concurrent(简称JUC)包,在此包中增加了在并发编程中很常用的工具类, 用于定义类似于线程的自定义子系统,包括线程池,异步IO和轻量级任务框架;还提供了用于多线程上下文中的 Collection实现等。 第二节 volatile volatile:易变的，不稳定的 在并发编程中的三个特性： （1）互斥性（原子性） （2）内存可见性 （3）指令重排序 int b=20; int a=10; int c=a+b; volatile 关键字: 当多个线程进行操作共享数据时,可以保证内存中的数据是可见的;相较于 synchronized 是一种较为轻量级的同步策略; volatile 不具备"互斥性"; volatile 不能保证变量的"原子性"; synchronized和volatile的区别： (1)synchronized可以实现互斥性和内存可见性,不能禁止指令重排序。 (2)volatile可以实现内存可见性,禁止指令重排序，不能保证原子性。 案例演示：内存可见性 public class

here is my problem: I have a script (let's call it comet.php) whic is requsted by an AJAX client script and wait for a change to happen like this: while(no_changes){ usleep(100000); //check for changes } I don't like this too much, it's not very scalable and it's (imho) "bad practice" I would like to improve this behaviour with a semaphore(?) or anyway concurrent programming technique. Can you please give me some tips on how to handle this? (I know, it's not a short answer, but a starting point would be enough.) Edit : what about LibEvent ? You can solve this problem using ZeroMQ . ZeroMQ is a

用途 多线程访问可变变量时，是非线程安全的。可能导致程序崩溃。此时，可以通过使用信号量（semaphore）技术，保证多线程处理某段代码时，后面线程等待前面线程执行，保证了多线程的安全性。使用方法记两个就行了，一个是wait（dispatch_semaphore_wait），一个是signal（dispatch_semaphore_signal）。根据dispatch_semaphore_wait的参数类型提示去创建信号量（dispatch_semaphore_t）即可。 感觉原理跟PV操作如出一辙。 不用semaphore时code: #import <Foundation/Foundation.h> int main(int argc, const char * argv[]) { @autoreleasepool { // insert code here... NSLog(@"Hello, World!"); NSMutableArray *lArrM = [NSMutableArray array]; for (int i = 0; i < 100; ++i) { dispatch_async(dispatch_get_global_queue(0, 0), ^{ [lArrM addObject:@(i)]; }); } } return 0; } 运行结果

What do I need and how can I use threads in C on Windows Vista? Could you please give me a simple code example? Here is the MSDN sample on how to use CreateThread() on Windows. The basic idea is you call CreateThread() and pass it a pointer to your thread function, which is what will be run on the target thread once it is created. The simplest code to do it is: #include <windows.h> DWORD WINAPI ThreadFunc(void* data) { // Do stuff. This will be the first function called on the new thread. // When this function returns, the thread goes away. See MSDN for more details. return 0; } int main() {