AutoResetEvent, ManualResetEvent是C#中常用的线程同步方法，在Java中可以模拟，AutoResetEvent使用Semaphore，增加的是许可证数量，程序里只有一个许可证，那么当这个许可被使用后，就会自动锁定。相反，ManualResetEvent使用countdownlatch，增加的是“latch”，也就是障碍，或者门闩；当障碍解除时，所有程序都可以运行而不被阻塞，如果要实现同步，就必须manual reset，也就是手动加latch。

import java.util.concurrent.Semaphore;

import java.util.concurrent.TimeUnit;

public class AutoResetEvent

{

private final Semaphore event;

private final Integer mutex;

public AutoResetEvent(boolean signalled)

{

event = new Semaphore(signalled ? 1 : 0);

mutex = new Integer(-1);

}

public void set()

{

synchronized (mutex)

{

if (event.availablePermits() == 0)

{

event.release();

}

}

}

public void reset()

{

event.drainPermits();

}

public void waitOne() throws InterruptedException

{

event.acquire();

}

public boolean waitOne(int timeout, TimeUnit unit) throws InterruptedException

{

return event.tryAcquire(timeout, unit);

}

public boolean isSignalled()

{

return event.availablePermits() > 0;

}

public boolean waitOne(int timeout) throws InterruptedException

{

return waitOne(timeout, TimeUnit.MILLISECONDS);

}

}

AutoResetEvent在MSDN中的例子程序在http://msdn.microsoft.com/en-us/library/system.threading.autoresetevent.aspx

我们可以改写一个java版本，用的是java版本的AutoResetEvent

import java.util.Date;

import java.util.Random;

class TermInfo

{

public long[] terms;

public int order;

public long baseValue;

public AutoResetEvent trigger;

}

public class AutoResetEventTest

{

private final static int numTerms = 3;

public static void main(String[] args0) throws InterruptedException

{

AutoResetEvent trigger = new AutoResetEvent(false);

TermInfo tinfo = new TermInfo();

Thread termThread;

long[] terms = new long[numTerms];

int result = 0;

tinfo.terms = terms;

tinfo.trigger = trigger;

for (int i = 0; i < numTerms; i++)

{

tinfo.order = i;

// Create and start the term calc thread.

TermThreadProc termThreadProc = new TermThreadProc(tinfo);

termThread = new Thread(termThreadProc);

termThread.start();

// simulate a number crunching delay

Thread.sleep(1000);

Date date = new Date();

tinfo.baseValue = Integer.parseInt(String.valueOf((date.getTime())).substring(10));

trigger.set();

termThread.join();

result += terms[i];

}

System.out.format("Result = %d", result);

System.out.println();

}

}

class TermThreadProc implements Runnable

{

public TermInfo termInfo;

public TermThreadProc(TermInfo termInfo)

{

this.termInfo = termInfo;

}

@Override

public void run()

{

TermInfo tinfo = termInfo;

System.out.format("Term[%d] is starting...", tinfo.order);

System.out.println();

// set the precalculation

Date date = new Date();

long preValue = Integer.parseInt(String.valueOf((date.getTime())).substring(10)) + tinfo.order;

// wait for base value to be ready

try

{

tinfo.trigger.waitOne();

}

catch (InterruptedException e)

{

e.printStackTrace();

}

Random rnd = new Random(tinfo.baseValue);

tinfo.terms[tinfo.order] = preValue * rnd.nextInt(10000);

System.out.format("Term[%d] has finished with a value of: %d", tinfo.order, tinfo.terms[tinfo.order]);

System.out.println();

}

}

//ManualResetEvent 的Java实现

import java.util.concurrent.CountDownLatch;

import java.util.concurrent.TimeUnit;

public class ManualResetEvent

{

private volatile CountDownLatch event;

private final Integer mutex;

public ManualResetEvent(boolean signalled)

{

mutex = new Integer(-1);

if (signalled)

{

event = new CountDownLatch(0);

}

else

{

event = new CountDownLatch(1);

}

}

public void set()

{

event.countDown();

}

public void reset()

{

synchronized (mutex)

{

if (event.getCount() == 0)

{

event = new CountDownLatch(1);

}

}

}

public void waitOne() throws InterruptedException

{

event.await();

}

public boolean waitOne(int timeout, TimeUnit unit) throws InterruptedException

{

return event.await(timeout, unit);

}

public boolean isSignalled()

{

return event.getCount() == 0;

}

public boolean waitOne(int timeout) throws InterruptedException

{

return waitOne(timeout, TimeUnit.MILLISECONDS);

}

}

MSDN地址：http://msdn.microsoft.com/en-us/library/system.threading.manualresetevent.aspx

Java测试：

import java.util.Scanner;

import java.io.IOException;

public class ManualResetEventTest

{

// mre is used to block and release threads manually. It is

// created in the unsignaled state.

static AutoResetEvent mre = new AutoResetEvent(false);

public static void main(String[] arg0) throws IOException, InterruptedException

{

System.out.println("\nStart 3 named threads that block on a ManualResetEvent:\n");

Scanner keyIn = new Scanner(System.in);

System.out.print("Press the enter key to continue");

keyIn.nextLine();

for (int i = 0; i <= 2; i++)

{

threadProc threadProc = new threadProc();

Thread t = new Thread(threadProc);

t.setName("Thread_" + i);

t.start();

}

Thread.sleep(500);

System.out.println("\nWhen all three threads have started, press Enter to call Set()"

+ "\nto release all the threads.\n");

keyIn.nextLine();

mre.set();

Thread.sleep(500);

System.out.println("\nWhen a ManualResetEvent is signaled, threads that call WaitOne()"

+ "\ndo not block. Press Enter to show this.\n");

keyIn.nextLine();

for (int i = 3; i <= 4; i++)

{

threadProc threadProc = new threadProc();

Thread t = new Thread(threadProc);

t.setName("Thread_" + i);

t.start();

}

Thread.sleep(500);

System.out.println("\nPress Enter to call Reset(), so that threads once again block"

+ "\nwhen they call WaitOne().\n");

keyIn.nextLine();

mre.reset();

// Start a thread that waits on the ManualResetEvent.

threadProc threadProc = new threadProc();

Thread t5 = new Thread(threadProc);

t5.setName("Thread_5");

t5.start();

Thread.sleep(500);

System.out.println("\nPress Enter to call Set() and conclude the demo.");

keyIn.nextLine();

mre.set();

}

}

class threadProc implements Runnable

{

@Override

public void run()

{

String name = Thread.currentThread().getName();

System.out.println(name + " starts and calls mre.WaitOne()");

try

{

ManualResetEventTest.mre.waitOne();

}

catch (InterruptedException e)

{

e.printStackTrace();

}

System.out.println(name + " ends.");

}

}

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2011-04-07 16:39

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