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使用ReentrantLock时出现死锁

multithreading java

javaworld · 技术社区 · 6 年前

使用ReentrantLock实现生产者-消费者问题的IM

public class Processor {
   Lock lock =  new ReentrantLock(true);
   Condition condn = lock.newCondition();
    public void produce() throws InterruptedException{
       lock.lock();
            System.out.println("inside producer method");
            condn.await();
            System.out.println("thread again wakeup");
        lock.unlock();
    }

    public void consume() throws InterruptedException{
          lock.lock();
            Thread.sleep(1000);
            condn.signal();
            System.out.println("will i ever be ok ");
            lock.unlock();
    }


}

ReentrantLock同步了两种方法,但有时进程会死锁

开/关我会没事的吗内部生产者法

运行堆转储时

引用处理程序“2守护程序prio=10操作系统prio=31 cpu=0.26ms已用时间=540.35s tid=0x00007fd5f186f800 nid=0x4603等待条件[0x000070000235700]

 java.lang.Thread.State: RUNNABLE
    at java.lang.ref.Reference.waitForReferencePendingList(java.base@11.0.1/Native Method)
    at java.lang.ref.Reference.processPendingReferences(java.base@11.0.1/Reference.java:241)
    at java.lang.ref.Reference$ReferenceHandler.run(java.base@11.0.1/Reference.java:213)

"Finalizer" #3 daemon prio=8 os_prio=31 cpu=0.67ms elapsed=540.35s tid=0x00007fd5f1883000 nid=0x4303 in Object.wait()  [0x000070000245a000]
   java.lang.Thread.State: WAITING (on object monitor)
    at java.lang.Object.wait(java.base@11.0.1/Native Method)
    - waiting on <0x0000000787f08f80> (a java.lang.ref.ReferenceQueue$Lock)
    at java.lang.ref.ReferenceQueue.remove(java.base@11.0.1/ReferenceQueue.java:155)
    - waiting to re-lock in wait() <0x0000000787f08f80> (a java.lang.ref.ReferenceQueue$Lock)
    at java.lang.ref.ReferenceQueue.remove(java.base@11.0.1/ReferenceQueue.java:176)
    at java.lang.ref.Finalizer$FinalizerThread.run(java.base@11.0.1/Finalizer.java:170)

"Signal Dispatcher" #4 daemon prio=9 os_prio=31 cpu=0.34ms elapsed=540.27s tid=0x00007fd5f1884000 nid=0x3903 waiting on condition  [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE


"Thread-0" #12 prio=5 os_prio=31 cpu=1.72ms elapsed=540.07s tid=0x00007fd5f00c7000 nid=0xa303 waiting on condition  [0x0000700002d75000]
   java.lang.Thread.State: WAITING (parking)
    at jdk.internal.misc.Unsafe.park(java.base@11.0.1/Native Method)
    - parking to wait for  <0x0000000787ed4030> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
    at java.util.concurrent.locks.LockSupport.park(java.base@11.0.1/LockSupport.java:194)
    at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(java.base@11.0.1/AbstractQueuedSynchronizer.java:2081)
    at Processor.produce(Processor.java:11)
    at RunnableExample$1.run(RunnableExample.java:13)
    at java.lang.Thread.run(java.base@11.0.1/Thread.java:834)

为什么在我使用

    condn.signal();

2 回复 | 直到 6 年前

xingbin 6 年前

如果消费者打电话 consume 先是制片人打电话 produce ,则制作人将错过 signal 然后被卡住。

Some Name 6 年前

你可以用 Phaser 为了这个。关键是 移相器 制片人问:“我错过了一些消费吗?”如果没有,它正在等待,如果是,它将立即进一步进行。下面是一个例子:

public class Processor {
   private final Phaser phaser = new Phaser(1);
   private volatile int lastPhaseId = 0;

    public void produce() throws InterruptedException{
            System.out.println("inside producer method");
            lastPhaseId = phaser.awaitAdvance(lastPhaseId);
            System.out.println("thread again wakeup");
    }

    public void consume() throws InterruptedException{
            Thread.sleep(1000);
            phaser.arrive();
            System.out.println("will i ever be ok ");
    }
}

这对单一消费者有效。如果假设多个消费者 phase.arrive() 需要互斥访问和/或注册方相应更改(取决于所需的语义)