Locked ownable synchronizers(转)
public class DeadLock {
public static void main(final String[] args) throws Exception {
final Object lock1 = new Object();
final Object lock2 = new Object();
Thread.currentThread().setName("main-thread");
final Thread r = new Thread("another-thread") {
@Override
public void run() {
try {
synchronized (lock2) {
Thread.sleep(20000);
synchronized (lock1) {
Thread.sleep(20000);
}
}
}
catch (final Exception e) {
e.printStackTrace();
}
}
};
r.start();
Thread.sleep(5000);
synchronized (lock1) {
Thread.sleep(20000);
synchronized (lock2) {
Thread.sleep(20000);
}
}
}
}
这段代码可能有点复杂,但原理不麻烦,就是描述了经典的加锁顺序问题。栈信息比较有趣,裁剪之后如下。
"another-thread" prio= tid=0x02b22400 nid=0x2250 waiting for monitor entry [0x0316f000]
java.lang.Thread.State: BLOCKED (on object monitor)
at DeadLock$.run(DeadLock.java:)
- waiting to lock <0x22bc3f90> (a java.lang.Object)
- locked <0x22bc3f98> (a java.lang.Object) Locked ownable synchronizers:
- None
"main-thread" prio= tid=0x00868800 nid=0x2634 waiting for monitor entry [0x0098f000]
java.lang.Thread.State: BLOCKED (on object monitor)
at DeadLock.main(DeadLock.java:)
- waiting to lock <0x22bc3f98> (a java.lang.Object)
- locked <0x22bc3f90> (a java.lang.Object) Locked ownable synchronizers:
- None
Found one Java-level deadlock:
=============================
"another-thread":
waiting to lock monitor 0x02ad433c (object 0x22bc3f90, a java.lang.Object),
which is held by "main-thread"
"main-thread":
waiting to lock monitor 0x02ad363c (object 0x22bc3f98, a java.lang.Object),
which is held by "another-thread" Java stack information for the threads listed above:
===================================================
"another-thread":
at DeadLock$.run(DeadLock.java:)
- waiting to lock <0x22bc3f90> (a java.lang.Object)
- locked <0x22bc3f98> (a java.lang.Object)
"main-thread":
at DeadLock.main(DeadLock.java:)
- waiting to lock <0x22bc3f98> (a java.lang.Object)
- locked <0x22bc3f90> (a java.lang.Object) Found deadlock.
主线程中提示了当前持有的锁和期望获取的锁,而新线程也存在类似的提示,只是获取锁的顺序不同。从栈信息可以看出,两个线程都处于BLOCKED状态。可能是源代码中的问题过于明显,导出的栈信息中给出了死锁的提示信息,实际项目的业务代码比样例要复杂,JVM可能做不到这么智能。这里的提示信息多多少少有点让我失望,在主线程栈信息的最后一部分没有输出当前持有锁的列表,很奇怪,不知道是不是和JDK的实现有关。
import java.security.SecureRandom;
import java.util.concurrent.SynchronousQueue;
import java.util.concurrent.ThreadFactory;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.locks.ReentrantLock; public class DeadLock {
private final ReentrantLock lock = new ReentrantLock();
private static final SecureRandom random = new SecureRandom(); public DeadLock() {
} public void runWork() { final ThreadPoolExecutor threadpool = new ThreadPoolExecutor(3, 3, 60L, TimeUnit.DAYS,
new SynchronousQueue<Runnable>(), new ThreadFactory() {
private final AtomicInteger counter = new AtomicInteger(1);
@Override
public Thread newThread(final Runnable r) {
return new Thread(r, "thread-sn-" + counter.getAndIncrement());
}
});
threadpool.setRejectedExecutionHandler(new ThreadPoolExecutor.CallerRunsPolicy());
Thread.currentThread().setName("main-thread");
for (int i = 0; i < 15; ++i) {
threadpool.submit(new Runnable() {
@Override
public void run() {
try { int timeout = 0;
while ((timeout = random.nextInt()) <= 0) {
}
timeout = timeout % 111;
Thread.sleep(timeout * 100L); lock.lock();
callLongTime(); }
catch (final Exception e) {
e.printStackTrace();
}
finally {
lock.unlock();
}
}
});
}
threadpool.shutdown();
} public static void main(final String[] args) throws Exception {
new DeadLock().runWork();
} static long callLongTime() {
System.out.println("thread name " + Thread.currentThread().getName());
long sum = 0;
for (long i = 0; i < 10000000000L; ++i) {
sum = sum ^ i + i;
}
return sum;
}
}
最后一个样例,写的比较复杂,但事情比较简单,线程之间的同步关键字换成了Java5提供的concurrent库中的重入锁。
"thread-sn-3" prio= tid=0x02de8400 nid=0x2688 runnable [0x0320f000]
java.lang.Thread.State: RUNNABLE
at DeadLock.callLongTime(DeadLock.java:)
at DeadLock$.run(DeadLock.java:)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:)
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:)
at java.util.concurrent.FutureTask.run(FutureTask.java:)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:)
at java.lang.Thread.run(Thread.java:) Locked ownable synchronizers:
- <0x22be1488> (a java.util.concurrent.locks.ReentrantLock$NonfairSync)
- <0x22be66d8> (a java.util.concurrent.ThreadPoolExecutor$Worker) "thread-sn-2" prio= tid=0x02de6c00 nid=0x218c waiting on condition [0x031bf000]
java.lang.Thread.State: WAITING (parking)
at sun.misc.Unsafe.park(Native Method)
- parking to wait for <0x22be1488> (a java.util.concurrent.locks.ReentrantLock$NonfairSync)
at java.util.concurrent.locks.LockSupport.park(LockSupport.java:)
at java.util.concurrent.locks.AbstractQueuedSynchronizer.parkAndCheckInterrupt(AbstractQueuedSynchronizer.java:)
at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireQueued(AbstractQueuedSynchronizer.java:)
at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquire(AbstractQueuedSynchronizer.java:)
at java.util.concurrent.locks.ReentrantLock$NonfairSync.lock(ReentrantLock.java:)
at java.util.concurrent.locks.ReentrantLock.lock(ReentrantLock.java:)
at DeadLock$.run(DeadLock.java:)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:)
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:)
at java.util.concurrent.FutureTask.run(FutureTask.java:)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:)
at java.lang.Thread.run(Thread.java:) Locked ownable synchronizers:
- <0x22be64e0> (a java.util.concurrent.ThreadPoolExecutor$Worker)
栈信息比较有趣,JVM在每个线程线的最后部分输出了当前线程持有的锁对象,类型和地址。从上述的信息中可以找到,当前处于运行状态的线程持有了一个地址为0x22be1488的锁,而这个锁正是其它线程等待获取的锁对象。
http://blog.csdn.net/jackie_xiaonan/article/details/8577785
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