yield
/**
* A hint to the scheduler that the current thread is willing to yield
* its current use of a processor. The scheduler is free to ignore this
* hint.
*
* <p> Yield is a heuristic attempt to improve relative progression
* between threads that would otherwise over-utilise a CPU. Its use
* should be combined with detailed profiling and benchmarking to
* ensure that it actually has the desired effect.
*
* <p> It is rarely appropriate to use this method. It may be useful
* for debugging or testing purposes, where it may help to reproduce
* bugs due to race conditions. It may also be useful when designing
* concurrency control constructs such as the ones in the
* {@link java.util.concurrent.locks} package.
*/
public static native void yield();
yield:英文意思是:屈服,退让。在线程中也有类似意思,意思是当前线程退让出使用权,把运行机会交给线程池中拥有相同优先级的线程。线程调用了yield方法,该线程就从运行状态变为可运行状态
join
public final synchronized void join(long millis)
throws InterruptedException {
long base = System.currentTimeMillis();
long now = 0;
if (millis < 0) {
throw new IllegalArgumentException("timeout value is negative");
}
if (millis == 0) {
while (isAlive()) {
wait(0);
}
} else {
while (isAlive()) {
long delay = millis - now;
if (delay <= 0) {
break;
}
wait(delay);
now = System.currentTimeMillis() - base;
}
}
}
join 底层还是运用wait,所以join的作用是谁调用,谁等待。比如:
Thread a = new Thread(() ->{
System.out.println("this is a");
});
a.start();
a.join();
System.out.println("this is main thread");
结果:
this is a
this is main thread
调用a.join()的是主线程,相当于主线程调用了wait方法,所以主线程等待a线程执行完了再执行。
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