一、操作系统层面的五种状态
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- 初始状态：仅是在语言层面创建了线程对象，还未与操作系统线程关联
- 可运行状态（就绪状态）：指该线程已经被创建（与操作系统线程关联），可以由 CPU 调度执行
-
运行状态：指获取了 CPU 时间片运行中的状态
- 当 CPU 时间片用完，会从
运行状态转换至可运行状态，会导致线程的上下文切换
- 当 CPU 时间片用完，会从
-
阻塞状态
- 如果调用了阻塞 API，如 BIO 读写文件，这时该线程实际不会用到 CPU，会导致线程上下文切换，进入
阻塞状态 - 等 BIO 操作完毕，会由操作系统唤醒阻塞的线程，转换至
可运行状态 - 与
可运行状态的区别是，对阻塞状态的线程来说只要它们一直不唤醒，调度器就一直不会考虑调度它们
- 如果调用了阻塞 API，如 BIO 读写文件，这时该线程实际不会用到 CPU，会导致线程上下文切换，进入
- 终止状态：表示线程已经执行完毕，生命周期已经结束，不会再转换为其它状态
二、 Java API 层面的六种状态
public enum State {
/**
* Thread state for a thread which has not yet started.
*/
NEW,
/**
* Thread state for a runnable thread. A thread in the runnable
* state is executing in the Java virtual machine but it may
* be waiting for other resources from the operating system
* such as processor.
*/
RUNNABLE,
/**
* Thread state for a thread blocked waiting for a monitor lock.
* A thread in the blocked state is waiting for a monitor lock
* to enter a synchronized block/method or
* reenter a synchronized block/method after calling
* {@link Object#wait() Object.wait}.
*/
BLOCKED,
/**
* Thread state for a waiting thread.
* A thread is in the waiting state due to calling one of the
* following methods:
* <ul>
* <li>{@link Object#wait() Object.wait} with no timeout</li>
* <li>{@link #join() Thread.join} with no timeout</li>
* <li>{@link LockSupport#park() LockSupport.park}</li>
* </ul>
*
* <p>A thread in the waiting state is waiting for another thread to
* perform a particular action.
*
* For example, a thread that has called <tt>Object.wait()</tt>
* on an object is waiting for another thread to call
* <tt>Object.notify()</tt> or <tt>Object.notifyAll()</tt> on
* that object. A thread that has called <tt>Thread.join()</tt>
* is waiting for a specified thread to terminate.
*/
WAITING,
/**
* Thread state for a waiting thread with a specified waiting time.
* A thread is in the timed waiting state due to calling one of
* the following methods with a specified positive waiting time:
* <ul>
* <li>{@link #sleep Thread.sleep}</li>
* <li>{@link Object#wait(long) Object.wait} with timeout</li>
* <li>{@link #join(long) Thread.join} with timeout</li>
* <li>{@link LockSupport#parkNanos LockSupport.parkNanos}</li>
* <li>{@link LockSupport#parkUntil LockSupport.parkUntil}</li>
* </ul>
*/
TIMED_WAITING,
/**
* Thread state for a terminated thread.
* The thread has completed execution.
*/
TERMINATED;
}
- NEW：线程刚被创建，但是还没有调用
start()方法 - RUNNABLE：当调用了
start()方法之后，Java API 层面的 RUNNABLE 状态涵盖了 操作系统 层面的可运行状态、运行状态和阻塞状态（由于 BIO 导致的线程阻塞，在 Java 里无法区分，仍然认为是可运行） - BLOCKED、WAITING、TIMED_WAITING：Java API 层面对
阻塞状态的细分 - TERMINATED：当线程代码运行结束
@Slf4j
public class StateTest {
public static void main(String[] args) throws IOException {
// new
Thread t1 = new Thread("t1") {
@Override
public void run() {
log.debug("running...");
}
};
Thread t2 = new Thread("t2") {
@Override
public void run() {
while(true) {
}
}
};
// runnable
t2.start();
Thread t3 = new Thread("t3") {
@Override
public void run() {
log.debug("running...");
}
};
// terminated
t3.start();
Thread t4 = new Thread("t4") {
@Override
public void run() {
synchronized (StateTest.class) {
try {
Thread.sleep(1000000);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
};
// timed_waiting
t4.start();
Thread t5 = new Thread("t5") {
@Override
public void run() {
try {
t2.join();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
};
// waiting
t5.start();
Thread t6 = new Thread("t6") {
@Override
public void run() {
synchronized (StateTest.class) {
try {
Thread.sleep(1000000);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
};
// blocked 拿不到锁
t6.start();
try {
Thread.sleep(500);
} catch (InterruptedException e) {
e.printStackTrace();
}
log.debug("t1 state {}", t1.getState());
log.debug("t2 state {}", t2.getState());
log.debug("t3 state {}", t3.getState());
log.debug("t4 state {}", t4.getState());
log.debug("t5 state {}", t5.getState());
log.debug("t6 state {}", t6.getState());
System.in.read();
}
}
15:16:58.719 [t3] DEBUG juc.thread.StateTest - running...
15:16:59.230 [main] DEBUG juc.thread.StateTest - t1 state NEW
15:16:59.238 [main] DEBUG juc.thread.StateTest - t2 state RUNNABLE
15:16:59.238 [main] DEBUG juc.thread.StateTest - t3 state TERMINATED
15:16:59.239 [main] DEBUG juc.thread.StateTest - t4 state TIMED_WAITING
15:16:59.239 [main] DEBUG juc.thread.StateTest - t5 state WAITING
15:16:59.239 [main] DEBUG juc.thread.StateTest - t6 state BLOCKED
三、线程状态转换
image.png
1.NEW --> RUNNABLE
当调用 t.start()方法时，由 NEW --> RUNNABLE
2.RUNNABLE <--> WAITING
t 线程用 synchronized(obj) 获取了对象锁后：
- 调用
obj.wait()方法时，t 线程从 RUNNABLE --> WAITING - 调用
obj.notify()，obj.notifyAll()，t.interrupt()时
竞争锁成功，t 线程从 WAITING --> RUNNABLE
竞争锁失败，t 线程从 WAITING --> BLOCKED
3.RUNNABLE <--> WAITING
- 当前线程调用
t.join()方法时，当前线程从 RUNNABLE --> WAITING（是当前线程在t 线程对象的监视器上等待） - t 线程运行结束，或调用了当前线程的
interrupt()时，当前线程从 WAITING --> RUNNABLE
4.RUNNABLE <--> WAITING
- 当前线程调用
LockSupport.park()方法会让当前线程从 RUNNABLE --> WAITING - 调用
LockSupport.unpark(目标线程)或调用了线程 的interrupt()，会让目标线程从 WAITING -->RUNNABLE
5.RUNNABLE <--> TIMED_WAITING
t 线程用 synchronized(obj) 获取了对象锁后：
- 调用
obj.wait(long n)方法时，t 线程从 RUNNABLE --> TIMED_WAITING - t 线程等待时间超过了 n 毫秒，或调用
obj.notify()，obj.notifyAll()，t.interrupt()时
竞争锁成功，t 线程从 TIMED_WAITING --> RUNNABLE
竞争锁失败，t 线程从 TIMED_WAITING --> BLOCKED
6.RUNNABLE <--> TIMED_WAITING
- 当前线程调用
t.join(long n)方法时，当前线程从 RUNNABLE --> TIMED_WAITING（当前线程在t 线程对象的监视器上等待） - 当前线程等待时间超过了 n 毫秒，或t 线程运行结束，或调用了当前线程的
interrupt()时，当前线程从TIMED_WAITING --> RUNNABLE
7.RUNNABLE <--> TIMED_WAITING
- 当前线程调用
Thread.sleep(long n)，当前线程从 RUNNABLE --> TIMED_WAITING - 当前线程等待时间超过了 n 毫秒，当前线程从 TIMED_WAITING --> RUNNABLE
8.RUNNABLE <--> TIMED_WAITING
- 当前线程调用
LockSupport.parkNanos(long nanos)或LockSupport.parkUntil(long millis)时，当前线程从 RUNNABLE --> TIMED_WAITING - 调用
LockSupport.unpark(目标线程)或调用了线程 的interrupt()，或是等待超时，会让目标线程从TIMED_WAITING--> RUNNABLE
9.RUNNABLE <--> BLOCKED
- t 线程用
synchronized(obj)获取了对象锁时如果竞争失败，从 RUNNABLE --> BLOCKED - 持 obj 锁线程的同步代码块执行完毕，会唤醒该对象上所有 BLOCKED 的线程重新竞争，如果其中 t 线程竞争成功，从 BLOCKED --> RUNNABLE ，其它失败的线程仍然 BLOCKED
10.RUNNABLE <--> TERMINATED
当前线程所有代码运行完毕，进入 TERMINATED
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