我有一个如下所示的 API,其中 Baz
是工作程序实现。
此 Bar
需要是线程安全的,这在与 Baz 的回调交互时会变得棘手。
回调中需要引用当前的baz实例(可以在工作线程上调用,也可以同步调用)。 评论应该显示问题:
final class Bar {
final Lock lock = new ReentrantLock();
Baz baz; // Guarded by lock.
void run() { // Called by any thread.
lock.lock();
if (baz.isRunning()) {
lock.unlock();
return;
}
baz = new Baz();
// If it unlocks here, the next line may execute on the wrong Baz.
// If it doesn't unlock here, there will be a deadlock when done() is called synchronously.
// lock.unlock();
baz.run(new Baz.Callback() { // May be called synchronously or by Baz worker thread.
@Override
public void done() {
lock.lock();
baz = new Baz();
lock.unlock();
}
});
}
}
有没有什么好的方法既可以使它正常工作又不会造成死锁?
编辑:更简洁:
final class Foo {
final Lock lock = new ReentrantLock();
void run() {
lock.lock();
worker.enqueue(new Callback() {
@Override void complete() {
lock.lock(); // Could cause deadlock.
}
});
lock.unlock();
}
}
最佳答案
不确定是否完全实现了您想要实现的目标,但也许这就是您正在寻找的东西?
final class Bar {
final Lock lock = new ReentrantLock();
Baz baz = new Baz();
void run() {
if (!lock.tryLock()) {
return;
}
try {
CountdownLatch callbackFlag = new CountdownLatch(1);
baz.run(new Baz.Callback() {
@Override
public void done() {
callbackFlag.countDown();
}
});
try {
callbackFlag.await(); // better use overloaded method with max timeout waiting. you don't probably want to wait forever
baz = new Baz(); // do you really want to reinit Baz on each execution?
} catch (InterruptedException e) {
// decide what you want to happen here
}
} finally {
lock.unlock();
}
}
}
关于java - 维护线程安全,同时防止可能发生同步回调的死锁,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/45382932/