线程生命周期
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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;
}
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在 Thread 类中，有如下常用的方法：
线程优先级
线程调度方式
- 抢占式调度：多个线程抢夺 CPU 的执行权，CPU 在什么时候执行哪条线程是不确定的，执行多长时间也是不确定的，所以抢占式调度它体现了一个随机性。
- 非抢占式调度 / 分时调度模型：所有线程轮流使用 CPU 的使用权，平均分配每个线程占用 CPU 的时间片 。
在 Java 当中，它采取了第一种抢占式调度模型的方式。
在 Thread 类中，最小优先级是 1，最大是 10，默认为 5，优先级越高，该线程抢到 cpu 执行权的机会越大（注意是机会很大，不是 100%）
守护线程
守护线程又叫备胎线程，通过 setDaemon()方法把当前线程设置为守护线程。
- 当仅剩的线程是非守护线程时，该线程会继续执行，当仅剩的线程是守护线程时，Java 虚拟机将直接退出
- 注意：setDaemon(true)方法必须在 start()方法前执行，否则会抛出 ILLegalThreadStateException 异常。
- 在守护线程中产生的新线程也是守护线程。
应用场景：在 QQ 聊天界面传输文件，如果在文件未传输完的情况下退出界面，那么文件就会传输中止
礼让线程
通过 yield()方法，当前线程将让出当前线程的执行权
插入线程
通过 join()方法，可以在线程 A 执行的时候，让线程 B 插队，等线程 B 执行完再执行线程 A，或者调用 join 方法时传入毫秒时间，让线程 B 插队的时间受控