java 线程的状态究竟意味着什么？

Question

我正在AndroidStudio学习工具，获取thread dump，如下：

我注意到像这样每个线程的不同状态，

我可以看到有 runnable、sleeping、waiting。而我深入线程栈，大部分线程栈都是这样的，

"<61> RxComputationScheduler-3@830064517520" daemon prio=5 waiting
    java.lang.Thread.State: WAITING
        at java.lang.Object.wait(Object.java:-1)
        at java.lang.Thread.parkFor(Thread.java:1205)
        at sun.misc.Unsafe.park(Unsafe.java:325)
        at java.util.concurrent.locks.LockSupport.park(LockSupport.java:157)
        at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:2017)
        at java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:1050)
        at java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:778)
        at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1035)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1097)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
        at java.lang.Thread.run(Thread.java:841)

我很困惑他们都在 Object.wait 停止，但是线程的状态可以是 runnable、sleeping、waiting?

这是其他状态线程的堆栈。

RUNNABLE

<53> RxSchedulerPurge-1@830057651944" daemon prio=5 runnable
  java.lang.Thread.State: RUNNABLE
      at java.lang.Object.wait(Object.java:-1)
      at java.lang.Thread.parkFor(Thread.java:1205)
      at sun.misc.Unsafe.park(Unsafe.java:325)
      at java.util.concurrent.locks.LockSupport.parkNanos(LockSupport.java:197)
      at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.awaitNanos(AbstractQueuedSynchronizer.java:2056)
      at java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:1062)
      at java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:778)
      at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1035)
      at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1097)
      at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
      at java.lang.Thread.run(Thread.java:841)</code>

TIMED_WAITING

<58> RxScheduledExecutorPool-2@830064740632" daemon prio=5 sleeping
  java.lang.Thread.State: TIMED_WAITING
      at java.lang.Object.wait(Object.java:-1)
      at java.lang.Thread.parkFor(Thread.java:1205)
      at sun.misc.Unsafe.park(Unsafe.java:325)
      at java.util.concurrent.locks.LockSupport.parkNanos(LockSupport.java:197)
      at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.awaitNanos(AbstractQueuedSynchronizer.java:2056)
      at java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:1062)
      at java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:778)
      at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1035)
      at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1097)
      at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
      at java.lang.Thread.run(Thread.java:841)

Answer 1

public static enum Thread.State
extends Enum<Thread.State>

线程状态。线程可以处于以下状态之一：

NEW
A thread that has not yet started is in this state.

RUNNABLE
A thread executing in the Java virtual machine is in this state.

BLOCKED
A thread that is blocked waiting for a monitor lock is in this state.

WAITING
A thread that is waiting indefinitely for another thread to perform a particular action is in this state.

TIMED_WAITING
A thread that is waiting for another thread to perform an action for up to a specified waiting time is in this state.

TERMINATED
A thread that has exited is in this state.

一个线程在给定的时间点只能处于一种状态。这些状态是不反映任何操作系统线程状态的虚拟机状态。

参考oracle's api了解更多信息。

Answer 2

New 表示如果您创建 Thread class 的实例但在调用 start() 方法之前线程处于新状态:

Thread t = new Thread(...); // t is New

Runnable表示调用start()方法后线程处于运行nable状态。基本上：

t.start(); // t is Runnable

运行是Runnable的"sub-state"：线程在运行ning如果线程调度程序已经 select 编辑它。你不能明确地对它做任何事情，这意味着你调用 start() 然后等待。

Ready是Runnable的另一个"sub-state"：线程有资格运行ning等待线程调度程序 select 它。

Blocked表示线程还活着时的状态，但是目前没有资格运行。例如，当一个线程遇到由另一个线程处理的 synchronized 块时，就会发生这种情况。在这种情况下，第一个线程变为 blocked.

Waiting 是您的线程既没有 blocked 也没有 ready 的状态。当您在线程上调用 wait() 或 join() 时通常会发生这种情况。

Thread t1 = new Thread(); // t1 is New
Thread t2 = new Thread(); // t2 is New
t1.start(); // t1 becomes Runnable
t2.start(); // t2 becomes Runnable
t1.join(); // t2 becomes Waiting, because t1 is processed until it terminates

还有一种叫Timed Waiting的状态，跟差不多，不过是调用sleep()造成的。如果调用 wait(timeout) 或 join(timeout)，线程也会进入 timed waiting 状态。

Thread t = new Thread(); // t is New
t.start(); // t is Runnable
t.sleep(4000); // t get state of Timed Waiting for 4 seconds

Terminated 是在 run() 方法退出时处于终止或死状态的线程。

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应 JoxTraex 的要求，以下是我在发帖前阅读的来源：

这只是谷歌搜索技巧的问题，真的...

java 线程的状态究竟意味着什么？

What does the java thread's state really mean?

java

performance

android

thread-dump

thread-state