更新：请参阅此问题的底部以获取完整答案。
我想运行一个辅助线程，以便我的主线程和我的辅助线程交替执行操作（不，我不想在主线程中执行所有操作，它是用于单元测试）。
我想出了两个不同的解决方案，我不知道哪个是最好的，我对第一个有疑问：
使用交换器
我想出了一个使用Exchanger的东西（虽然我不想只交换一个对象）。
@Test
public void launchMyTest() {
/**
* An anonymous class to set some variables from a different thread
*/
class ThreadTest extends Thread {
//declare some various attributes that will be set
//NOT DECLARED VOLATILE
...
public final Exchanger<Integer> exchanger = new Exchanger<Integer>();
@Override
public void run() {
try {
//start of the synchronization
int turn = 1;
while (turn != 2) {
turn = this.exchanger.exchange(turn);
}
//do some work and set my various variables
...
//main thread's turn
turn = 1;
this.exchanger.exchange(turn);
//wait for this thread's turn
while (turn != 2) {
turn = this.exchanger.exchange(turn);
}
//redo some other work and reset the various variables
...
//main thread's turn
turn = 1;
this.exchanger.exchange(turn);
} catch (InterruptedException e) {
Thread.currentThread().interrupt();
}
}
}
try {
//some work in the main thread
....
//launch the job in the second thread
ThreadTest test = new ThreadTest();
test.start();
//start of the synchronization
int turn = 2;
test.exchanger.exchange(turn);
//wait for this thread's turn
while (turn != 1) {
turn = test.exchanger.exchange(turn);
}
//run some tests using the various variables of the anonymous class
....
//now, relaunch following operations in the second thread
turn = 2;
test.exchanger.exchange(turn);
//wait for this thread's turn
while (turn != 1) {
turn = test.exchanger.exchange(turn);
}
//do some other tests using the various variables of the anonymous class
//...
} catch (InterruptedException e) {
Thread.currentThread().interrupt();
}
}
问题：
- 我是否正确，该
exchange方法执行内存同步，就像使用Lock?
使用条件
使用Condition的另一种解决方案：
@Test
public void launchMyTest() {
/**
* An anonymous class to set some variables from a different thread
*/
class ThreadTest extends Thread {
//declare some various attributes that will be set
//NOT DECLARED VOLATILE
...
public final Lock lock = new ReentrantLock();
public final Condition oneAtATime = lock.newCondition();
public int turn = 1;
@Override
public void run() {
this.lock.lock();
try {
//do some work and set my various variables
...
//main thread's turn
this.turn = 1;
this.oneAtATime.signal();
//wait for this thread's turn
while (this.turn != 2) {
this.oneAtATime.await();
}
//redo some other work and reset the various variables
...
//main thread's turn
this.turn = 1;
this.oneAtATime.signal();
} catch (InterruptedException e) {
Thread.currentThread().interrupt();
} finally {
this.lock.unlock();
}
}
}
ThreadTest test = new ThreadTest();
test.lock.lock();
try {
//some work in the main thread
....
//launch the job in the second thread
test.turn = 2;
test.start();
//wait for this thread's turn
while (test.turn != 1) {
test.oneAtATime.await();
}
//run some tests using the various variables of the anonymous class
....
//now, relaunch following operations in the second thread
test.turn = 2;
test.oneAtATime.signal();
//wait for this thread's turn
while (test.turn != 1) {
test.oneAtATime.await();
}
//do some other tests using the various variables of the anonymous class
//...
} catch (InterruptedException e) {
Thread.currentThread().interrupt();
} finally {
test.lock.unlock();
}
}
在我看来，这有点复杂。
结论
你认为最好的解决方案是什么？我做得对吗，还是我错过了另一个明显的解决方案？
我没有使用 aCountDownLatch因为我想交替运行多个CountDownLatch操作，并且无法重置。而且我没有发现CyclicBarrier是让代码更简单...（实际上我并没有完全理解如何使用它，但它看起来并不比使用简单Exchangeror Condition）
谢谢你。
更新
@Clément MATHIEU 提供了如何实现这一目标的不同示例，在其接受的答案的评论中，请参阅：https ://gist.github.com/cykl/5131021
有三个示例，一个使用 a CyclicBarrier，另一个使用 an Exchanger，最后一个使用 2 Semaphores。虽然他说“更具表现力的是基于信号量的”是正确的，但Exchanger为了简单起见，我选择使用 an 。我的单元测试变成了：
@Test
public void launchMyTest() {
/**
* An anonymous class to set some variables from a different thread
*/
class ThreadTest extends Thread {
//declare some various attributes that will be set
//NOT DECLARED VOLATILE
...
public final Exchanger<Integer> exchanger = new Exchanger<Integer>();
@Override
public void run() {
try {
//do some work and set my various variables
...
//main thread's turn
this.exchanger.exchange(null);
//wait for this thread's turn
this.exchanger.exchange(null);
//redo some other work and reset the various variables
...
//main thread's turn
this.exchanger.exchange(null);
} catch (InterruptedException e) {
Thread.currentThread().interrupt();
}
}
}
try {
//some work in the main thread
....
//launch the job in the second thread
ThreadTest test = new ThreadTest();
test.start();
//wait for this thread's turn
test.exchanger.exchange(null);
//run some tests using the various variables of the anonymous class
....
//now, relaunch following operations in the second thread
test.exchanger.exchange(null);
//wait for this thread's turn
test.exchanger.exchange(null);
//do some other tests using the various variables of the anonymous class
//...
} catch (InterruptedException e) {
Thread.currentThread().interrupt();
}
}