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Visual C#中编写多线程程序之起步

2024-07-21 02:29:37
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  .net将关于多线程的功能定义在system.threading名字空间中。因此,要使用多线程,必须先声明引用此名字空间(using system.threading;)。

  即使你没有编写多线程应用程序的经验,也可能听说过“启动线程”“杀死线程”这些词,其实除了这两个外,涉及多线程方面的还有诸如“暂停线程”“优先级”“挂起线程”“恢复线程”等等。下面将一个一个的解释。

  a.启动线程

  顾名思义,“启动线程”就是新建并启动一个线程的意思,如下代码可实现:

thread thread1 = new thread(new threadstart( count));

  其中的 count 是将要被新线程执行的函数。

  b.杀死线程

  “杀死线程”就是将一线程斩草除根,为了不白费力气,在杀死一个线程前最好先判断它是否还活着(通过 isalive 属性),然后就可以调用 abort 方法来杀死此线程。

  c.暂停线程

  它的意思就是让一个正在运行的线程休眠一段时间。如 thread.sleep(1000); 就是让线程休眠1秒钟。

  d.优先级

  这个用不着解释了。thread类中有一个threadpriority属性,它用来设置优先级,但不能保证操作系统会接受该优先级。一个线程的优先级可 分为5种:normal, abovenormal, belownormal, highest, lowest。具体实现例子如下:

thread.priority = threadpriority.highest;

  e.挂起线程

  thread类的suspend方法用来挂起线程,知道调用resume,此线程才可以继续执行。如果线程已经挂起,那就不会起作用。

if (thread.threadstate = threadstate.running)
{
 thread.suspend();
}

  f.恢复线程

  用来恢复已经挂起的线程,以让它继续执行,如果线程没挂起,也不会起作用。

if (thread.threadstate = threadstate.suspended)
{
 thread.resume();
}

  下面将列出一个例子,以说明简单的线程处理功能。此例子来自于帮助文档。

using system;
using system.threading;
// simple threading scenario: start a static method running
// on a second thread.
public class threadexample {
 // the threadproc method is called when the thread starts.
 // it loops ten times, writing to the console and yielding
 // the rest of its time slice each time, and then ends.
 public static void threadproc() {
  for (int i = 0; i < 10; i++) {
   console.writeline("threadproc: {0}", i);
   // yield the rest of the time slice.
   thread.sleep(0);
  }
 }

 public static void main() {
  console.writeline("main thread: start a second thread.");
  // the constructor for the thread class requires a threadstart
  // delegate that represents the method to be executed on the
  // thread. c# simplifies the creation of this delegate.
  thread t = new thread(new threadstart(threadproc));
  // start threadproc. on a uniprocessor, the thread does not get
  // any processor time until the main thread yields. uncomment
  // the thread.sleep that follows t.start() to see the difference.
  t.start();
  //thread.sleep(0);

  for (int i = 0; i < 4; i++) {
   console.writeline("main thread: do some work.");
   thread.sleep(0);
  }

  console.writeline("main thread: call join(), to wait until threadproc ends.");
  t.join();
  console.writeline("main thread: threadproc.join has returned. press enter to end program.");
  console.readline();
 }
}

  此代码产生的输出类似如下内容:

main thread: start a second thread.
main thread: do some work.
threadproc: 0
main thread: do some work.
threadproc: 1
main thread: do some work.
threadproc: 2
main thread: do some work.
threadproc: 3
main thread: call join(), to wait until threadproc ends.
threadproc: 4
threadproc: 5
threadproc: 6
threadproc: 7
threadproc: 8
threadproc: 9
main thread: threadproc.join has returned. press enter to end program.
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