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Java线程阻塞状态

news 2025/10/23 9:30:08

1 概述

Java线程提供了六种状态，其中三种是阻塞状态，用例子来了解一下这些阻塞状态，方便使用堆栈信息里的线程状态来协助定位问题。

2 线程的状态和转换

2.1 六种状态

JDK提供的线程支持六种状态，可以通过java.lang.Thread.State类定义来了解。
  • NEW：新建的线程，但还没有运行。这个在堆栈中不体现。
  • RUNNABLE：运行中的线程。
  • BLOCK/WAITING/TIMED_WAITING：阻塞的线程。
  • TERMINATED：运行结束的线程。
// java.lang.Thread.State
public enum State {NEW,RUNNABLE,BLOCKED,WAITING,TIMED_WAITING,TERMINATED;
}

2.2 synchronized阻塞的线程

下面例子使用synchronized关键字来提供锁，观察没有拿到锁的线程状态。

public class TestTask1 extends Thread {private final Object lock;private final String taskName;public TestTask1(String taskName, Object lock) {this.lock = lock;this.taskName = taskName;setName(taskName);}@Overridepublic void run() {synchronized (lock) {System.out.println("Running in " + taskName);try {Thread.sleep(100000); // 使用sleep()} catch (InterruptedException e) {throw new RuntimeException(e);}}}
}public class ThreadStatusDemo1 {public static void main(String[] args) {ThreadStatusDemo1 demo = new ThreadStatusDemo1();demo.test();}private void test() {Object lock = new Object();TestTask1 t1 = new TestTask1("my-test-1", lock);TestTask1 t2 = new TestTask1("my-test-2", lock);t1.start();t2.start();try {t1.join();t2.join();} catch (InterruptedException e) {e.printStackTrace();}}
}

打印堆栈信息：

"main" #1 prio=5 os_prio=0 tid=0x0000000002e84800 nid=0x7b80 in Object.wait() [0x0000000002caf000]java.lang.Thread.State: WAITING (on object monitor)at java.lang.Object.wait(Native Method)- waiting on <0x0000000718f992b0> (a com.qqian.stepfmk.srvpro.tstatus.TestTask)at java.lang.Thread.join(Thread.java:1245)- locked <0x0000000718f992b0> (a com.qqian.stepfmk.srvpro.tstatus.TestTask)at java.lang.Thread.join(Thread.java:1319)at com.qqian.stepfmk.srvpro.tstatus.ThreadStatusDemo.test(ThreadStatusDemo.java:16)at com.qqian.stepfmk.srvpro.tstatus.ThreadStatusDemo.main(ThreadStatusDemo.java:6)Locked ownable synchronizers:- None"my-test-1" #20 prio=5 os_prio=0 tid=0x000000002aea7000 nid=0x6918 waiting on condition [0x000000002c30e000]java.lang.Thread.State: TIMED_WAITING (sleeping)at java.lang.Thread.sleep(Native Method)at com.qqian.stepfmk.srvpro.tstatus.TestTask.run(TestTask.java:16)- locked <0x0000000718f95d80> (a java.lang.Object)Locked ownable synchronizers:- None"my-test-2" #21 prio=5 os_prio=0 tid=0x000000002aeaa000 nid=0x85c4 waiting for monitor entry [0x000000002c40f000]java.lang.Thread.State: BLOCKED (on object monitor)at com.qqian.stepfmk.srvpro.tstatus.TestTask.run(TestTask.java:14)- waiting to lock <0x0000000718f95d80> (a java.lang.Object)Locked ownable synchronizers:- None
从堆栈信息可以看出（线程1抢到锁）：
  • 用synchronized阻塞的线程（没有拿到锁），状态为BLOCKED。
  • 线程1抢到锁，里面用了Thread.sleep(timeout)，状态为TIMED_WAITING。
  • main线程用了Thread.join()，不带参数，状态为WAITING。

2.3 Ojbect.wait()阻塞

还是使用synchronized加锁，但在代码块里用了Object.wait()方法来等待。

public class TestTask3 extends Thread {private final Object lock;private final String taskName;public TestTask3(String taskName, Object lock) {this.lock = lock;this.taskName = taskName;setName(taskName);}@Overridepublic void run() {synchronized (lock) {System.out.println("Running in " + taskName);try {lock.wait(); // 使用wait()等待} catch (InterruptedException e) {throw new RuntimeException(e);}}}
}public class ThreadStatusDemo3 {public static void main(String[] args) {ThreadStatusDemo3 demo = new ThreadStatusDemo3();demo.test();}private void test() {Object lock = new Object();TestTask3 t1 = new TestTask3("my-test-1", lock);TestTask3 t2 = new TestTask3("my-test-2", lock);t1.start();t2.start();try {t1.join(10000000);t2.join();} catch (InterruptedException e) {e.printStackTrace();}}
}

打印堆栈信息：

"main" #1 prio=5 os_prio=0 tid=0x0000000002d35000 nid=0x8444 in Object.wait() [0x0000000002b4f000]java.lang.Thread.State: TIMED_WAITING (on object monitor)at java.lang.Object.wait(Native Method)- waiting on <0x00000007194ae888> (a com.qqian.stepfmk.srvpro.tstatus.TestTask3)at java.lang.Thread.join(Thread.java:1253)- locked <0x00000007194ae888> (a com.qqian.stepfmk.srvpro.tstatus.TestTask3)at com.qqian.stepfmk.srvpro.tstatus.ThreadStatusDemo3.test(ThreadStatusDemo3.java:16)at com.qqian.stepfmk.srvpro.tstatus.ThreadStatusDemo3.main(ThreadStatusDemo3.java:6)Locked ownable synchronizers:- None"my-test-1" #23 prio=5 os_prio=0 tid=0x000000002bb9f800 nid=0x5c10 in Object.wait() [0x000000002c42e000]java.lang.Thread.State: WAITING (on object monitor)at java.lang.Object.wait(Native Method)- waiting on <0x00000007194aad28> (a java.lang.Object)at java.lang.Object.wait(Object.java:502)at com.qqian.stepfmk.srvpro.tstatus.TestTask3.run(TestTask3.java:16)- locked <0x00000007194aad28> (a java.lang.Object)Locked ownable synchronizers:- None"my-test-2" #24 prio=5 os_prio=0 tid=0x000000002bba0000 nid=0x50d0 in Object.wait() [0x000000002c52e000]java.lang.Thread.State: WAITING (on object monitor)at java.lang.Object.wait(Native Method)- waiting on <0x00000007194aad28> (a java.lang.Object)at java.lang.Object.wait(Object.java:502)at com.qqian.stepfmk.srvpro.tstatus.TestTask3.run(TestTask3.java:16)- locked <0x00000007194aad28> (a java.lang.Object)Locked ownable synchronizers:- None
从上面堆栈可以看出：
  • Object.wait()会释放锁，所以两个线程都阻塞在了wait()处，线程状态都为WAITING。
  • Thread.join(timeout)带参数时，线程状态为TIMED_WAITING。

2.4 Object.wait(timeout)阻塞

还是使用synchronized加锁，在代码块里用了Object.wait(timeout)方法来等待，增加了timeout参数。

public class TestTask3 extends Thread {private final Object lock;private final String taskName;public TestTask3(String taskName, Object lock) {this.lock = lock;this.taskName = taskName;setName(taskName);}@Overridepublic void run() {synchronized (lock) {System.out.println("Running in " + taskName);try {lock.wait(100000); // 增加timeout参数} catch (InterruptedException e) {throw new RuntimeException(e);}}}
}public class ThreadStatusDemo3 {public static void main(String[] args) {ThreadStatusDemo3 demo = new ThreadStatusDemo3();demo.test();}private void test() {Object lock = new Object();TestTask3 t1 = new TestTask3("my-test-1", lock);TestTask3 t2 = new TestTask3("my-test-2", lock);t1.start();t2.start();try {t1.join(10000000);t2.join();} catch (InterruptedException e) {e.printStackTrace();}}
}

打印堆栈信息：

"main" #1 prio=5 os_prio=0 tid=0x00000000039c4800 nid=0x7f5c in Object.wait() [0x00000000037df000]java.lang.Thread.State: TIMED_WAITING (on object monitor)at java.lang.Object.wait(Native Method)- waiting on <0x0000000718f992d0> (a com.qqian.stepfmk.srvpro.tstatus.TestTask3)at java.lang.Thread.join(Thread.java:1253)- locked <0x0000000718f992d0> (a com.qqian.stepfmk.srvpro.tstatus.TestTask3)at com.qqian.stepfmk.srvpro.tstatus.ThreadStatusDemo3.test(ThreadStatusDemo3.java:16)at com.qqian.stepfmk.srvpro.tstatus.ThreadStatusDemo3.main(ThreadStatusDemo3.java:6)Locked ownable synchronizers:- None"my-test-1" #20 prio=5 os_prio=0 tid=0x000000002b9a3000 nid=0x24cc in Object.wait() [0x000000002ce5f000]java.lang.Thread.State: TIMED_WAITING (on object monitor)at java.lang.Object.wait(Native Method)- waiting on <0x0000000718f95d80> (a java.lang.Object)at com.qqian.stepfmk.srvpro.tstatus.TestTask3.run(TestTask3.java:16)- locked <0x0000000718f95d80> (a java.lang.Object)Locked ownable synchronizers:- None"my-test-2" #21 prio=5 os_prio=0 tid=0x000000002b9a4000 nid=0x3b0c in Object.wait() [0x000000002cf5f000]java.lang.Thread.State: TIMED_WAITING (on object monitor)at java.lang.Object.wait(Native Method)- waiting on <0x0000000718f95d80> (a java.lang.Object)at com.qqian.stepfmk.srvpro.tstatus.TestTask3.run(TestTask3.java:16)- locked <0x0000000718f95d80> (a java.lang.Object)Locked ownable synchronizers:- None
从上面可以看出：
  • Object.wait(timeout)会释放锁，所以两个线程都阻塞在了wait()处，线程状态都为TIMED_WAITING。

2.5 ReentrantLock.lock()阻塞

把锁换成ReentrantLock，不使用timeout参数：
import java.util.concurrent.locks.ReentrantLock;public class TestTask2 extends Thread {private final ReentrantLock lock;private final String taskName;public TestTask2(String taskName, ReentrantLock lock) {this.lock = lock;this.taskName = taskName;setName(taskName);}@Overridepublic void run() {try {lock.lock(); // 改为用ReentrantLock锁，不带timeout参数System.out.println("Running in " + taskName);try {Thread.sleep(100000);} catch (InterruptedException e) {throw new RuntimeException(e);}} finally {lock.unlock();}}
}public class ThreadStatusDemo2 {public static void main(String[] args) {ThreadStatusDemo2 demo = new ThreadStatusDemo2();demo.test();}private void test() {ReentrantLock lock = new ReentrantLock();TestTask2 t1 = new TestTask2("my-test-1", lock);TestTask2 t2 = new TestTask2("my-test-2", lock);t1.start();t2.start();try {t1.join();t2.join();} catch (InterruptedException e) {e.printStackTrace();}}
}

打印堆栈信息：

"main" #1 prio=5 os_prio=0 tid=0x0000000003134800 nid=0x66dc in Object.wait() [0x0000000002edf000]java.lang.Thread.State: WAITING (on object monitor)at java.lang.Object.wait(Native Method)- waiting on <0x0000000718f9f390> (a com.qqian.stepfmk.srvpro.tstatus.TestTask2)at java.lang.Thread.join(Thread.java:1245)- locked <0x0000000718f9f390> (a com.qqian.stepfmk.srvpro.tstatus.TestTask2)at java.lang.Thread.join(Thread.java:1319)at com.qqian.stepfmk.srvpro.tstatus.ThreadStatusDemo2.test(ThreadStatusDemo2.java:18)at com.qqian.stepfmk.srvpro.tstatus.ThreadStatusDemo2.main(ThreadStatusDemo2.java:8)Locked ownable synchronizers:- None"my-test-1" #20 prio=5 os_prio=0 tid=0x000000002af7b800 nid=0x6e78 waiting on condition [0x000000002c50f000]java.lang.Thread.State: TIMED_WAITING (sleeping)at java.lang.Thread.sleep(Native Method)at com.qqian.stepfmk.srvpro.tstatus.TestTask2.run(TestTask2.java:19)Locked ownable synchronizers:- <0x0000000718f9bd80> (a java.util.concurrent.locks.ReentrantLock$NonfairSync)"my-test-2" #21 prio=5 os_prio=0 tid=0x000000002af7c000 nid=0x88c4 waiting on condition [0x000000002c60e000]java.lang.Thread.State: WAITING (parking)at sun.misc.Unsafe.park(Native Method)- parking to wait for  <0x0000000718f9bd80> (a java.util.concurrent.locks.ReentrantLock$NonfairSync)at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)at java.util.concurrent.locks.AbstractQueuedSynchronizer.parkAndCheckInterrupt(AbstractQueuedSynchronizer.java:836)at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireQueued(AbstractQueuedSynchronizer.java:870)at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquire(AbstractQueuedSynchronizer.java:1199)at java.util.concurrent.locks.ReentrantLock$NonfairSync.lock(ReentrantLock.java:209)at java.util.concurrent.locks.ReentrantLock.lock(ReentrantLock.java:285)at com.qqian.stepfmk.srvpro.tstatus.TestTask2.run(TestTask2.java:16)Locked ownable synchronizers:- None
从上面可以看出：
  • ReentrantLock.lock()最终调的是sun.misc.Unsafe.park()来阻塞，线程状态为WAITING，并不是BLOCKED。

2.6 ReentrantLock.tryLock(timeout)阻塞

把锁换成ReentrantLock，使用timeout参数：
import java.util.concurrent.locks.ReentrantLock;public class TestTask2 extends Thread {private final ReentrantLock lock;private final String taskName;public TestTask2(String taskName, ReentrantLock lock) {this.lock = lock;this.taskName = taskName;setName(taskName);}@Overridepublic void run() {try {lock.tryLock(100000, TimeUnit.MILLISECONDS); // 改为带timeout参数System.out.println("Running in " + taskName);try {Thread.sleep(100000);} catch (InterruptedException e) {throw new RuntimeException(e);}} catch (InterruptedException e) {throw new RuntimeException(e);} finally {lock.unlock();}}
}public class ThreadStatusDemo2 {public static void main(String[] args) {ThreadStatusDemo2 demo = new ThreadStatusDemo2();demo.test();}private void test() {ReentrantLock lock = new ReentrantLock();TestTask2 t1 = new TestTask2("my-test-1", lock);TestTask2 t2 = new TestTask2("my-test-2", lock);t1.start();t2.start();try {t1.join();t2.join();} catch (InterruptedException e) {e.printStackTrace();}}
}

堆栈信息：

"main" #1 prio=5 os_prio=0 tid=0x0000000003c44800 nid=0x12f0 in Object.wait() [0x000000000397f000]java.lang.Thread.State: WAITING (on object monitor)at java.lang.Object.wait(Native Method)- waiting on <0x0000000718f9f4e0> (a com.qqian.stepfmk.srvpro.tstatus.TestTask2)at java.lang.Thread.join(Thread.java:1245)- locked <0x0000000718f9f4e0> (a com.qqian.stepfmk.srvpro.tstatus.TestTask2)at java.lang.Thread.join(Thread.java:1319)at com.qqian.stepfmk.srvpro.tstatus.ThreadStatusDemo2.test(ThreadStatusDemo2.java:18)at com.qqian.stepfmk.srvpro.tstatus.ThreadStatusDemo2.main(ThreadStatusDemo2.java:8)Locked ownable synchronizers:- None"my-test-1" #20 prio=5 os_prio=0 tid=0x000000002bb53800 nid=0x7a80 waiting on condition [0x000000002d00f000]java.lang.Thread.State: TIMED_WAITING (sleeping)at java.lang.Thread.sleep(Native Method)at com.qqian.stepfmk.srvpro.tstatus.TestTask2.run(TestTask2.java:20)Locked ownable synchronizers:- <0x0000000718f9b9a0> (a java.util.concurrent.locks.ReentrantLock$NonfairSync)"my-test-2" #21 prio=5 os_prio=0 tid=0x000000002bb56000 nid=0x391c waiting on condition [0x000000002d10f000]java.lang.Thread.State: TIMED_WAITING (parking)at sun.misc.Unsafe.park(Native Method)- parking to wait for  <0x0000000718f9b9a0> (a java.util.concurrent.locks.ReentrantLock$NonfairSync)at java.util.concurrent.locks.LockSupport.parkNanos(LockSupport.java:215)at java.util.concurrent.locks.AbstractQueuedSynchronizer.doAcquireNanos(AbstractQueuedSynchronizer.java:934)at java.util.concurrent.locks.AbstractQueuedSynchronizer.tryAcquireNanos(AbstractQueuedSynchronizer.java:1247)at java.util.concurrent.locks.ReentrantLock.tryLock(ReentrantLock.java:442)at com.qqian.stepfmk.srvpro.tstatus.TestTask2.run(TestTask2.java:17)Locked ownable synchronizers:- None
从上面可以看出：
  • ReentrantLock.tryLock(timeout)最终调的是sun.misc.Unsafe.park()来阻塞，线程状态为TIMED_WAITING，并不是BLOCKED。

3 小结

1、当由synchronized关键字提供的锁阻塞没有取到锁的线程时，状态为BLOCKED，其它锁阻塞的都不是BLOCKED状态。
2、锁时通过Unsafe.park()阻塞、调用Object.wait()、Thread.join()时，线程状态为WAITING。
3、锁是通过Unsafe.park(timeout)阻塞、调用Object.wait(timeout)、Thread.sleep(timeout)、Thread.join(timeout)时，线程状态为TIMED_WAITING。
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