sleep
1.sleep是Thread的一个静态(static)方法。使得Runnable实现的线程也可以使用sleep方法。而且避免了线程之前相互调用sleep()方法,引发死锁。
2.sleep()执行时需要赋予一个沉睡时间。在沉睡期间(阻塞线程期间),CPU会放弃这个线程,执行其他任务。当沉睡时间到了之后,该线程会自动苏醒,不过此时线程不会立刻被执行,而是要等CPU分配资源,和其他线程进行竞争。
3.此外如果这个线程之前获取了一个机锁,在沉睡期间,这个机锁不会释放。其他等待这个机锁的程序,必须等待这个线程醒来,且执行完后才能运行。
sleep相关代码
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public class ThreadTest2 {
public static void main(String[] args){
System.out.println( "begin our test" );
ThreadSleep sleep = new ThreadSleep();
try {
Thread thread1 = new Thread(sleep, "路人甲" );
Thread thread2 = new Thread(sleep, "路人乙" );
thread1.start();
thread2.start();
} catch (Exception e){
e.printStackTrace();
}
System.out.println( "test is over" );
}
}
class ThreadSleep implements Runnable{
int count = 0 ;
@Override
public void run(){
System.out.println(Thread.currentThread().getName() + " say : hello sleep !!" );
count();
}
public void count(){
while (count < 20 ) {
System.out.println(Thread.currentThread().getName() + " say : count is " + count);
try {
count++;
Thread.sleep( 100 );
} catch (Exception e) {
e.printStackTrace();
}
}
}
}
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输出日志
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begin our test
test is over
路人甲 say : hello sleep !!
路人甲 say : count is 0
路人乙 say : hello sleep !!
路人乙 say : count is 1
路人甲 say : count is 2
路人乙 say : count is 2
路人甲 say : count is 4
路人乙 say : count is 4
路人甲 say : count is 6
路人乙 say : count is 7
路人乙 say : count is 8
路人甲 say : count is 8
路人甲 say : count is 10
路人乙 say : count is 10
路人乙 say : count is 12
路人甲 say : count is 12
路人乙 say : count is 14
路人甲 say : count is 14
路人甲 say : count is 16
路人乙 say : count is 16
路人甲 say : count is 18
路人乙 say : count is 18
|
通过日志可以发现线程甲和线程乙基本是交替执行,但是并不规律,且出现了并发问题。
该情况是由于代码中设置了睡眠时间为100毫秒,由于count递增执行速度很快,所以线程差不多是同时睡眠,然后同时苏醒并导致了并发的出现。
接下来要添加synchronize块,检查sleep时机锁是否释放
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public class ThreadTest2 {
public static void main(String[] args){
System.out.println( "begin our test" );
ThreadSleep sleep = new ThreadSleep();
try {
Thread thread1 = new Thread(sleep, "路人甲" );
Thread thread2 = new Thread(sleep, "路人乙" );
thread1.start();
thread2.start();
} catch (Exception e){
e.printStackTrace();
}
System.out.println( "test is over" );
}
}
class ThreadSleep implements Runnable{
int count = 0 ;
@Override
public void run(){
System.out.println(Thread.currentThread().getName() + " say : hello sleep !!" );
count();
}
public void count(){
while (count < 20 ) {
synchronized ( this ) {
System.out.println(Thread.currentThread().getName() + " say : count is " + count);
try {
count++;
Thread.sleep( 100 );
} catch (Exception e) {
e.printStackTrace();
}
}
}
}
}
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输出日志
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begin our test
路人甲 say : hello sleep !!
路人甲 say : count is 0
test is over
路人乙 say : hello sleep !!
路人甲 say : count is 1
路人甲 say : count is 2
路人甲 say : count is 3
路人甲 say : count is 4
路人甲 say : count is 5
路人甲 say : count is 6
路人甲 say : count is 7
路人甲 say : count is 8
路人甲 say : count is 9
路人甲 say : count is 10
路人甲 say : count is 11
路人甲 say : count is 12
路人甲 say : count is 13
路人甲 say : count is 14
路人甲 say : count is 15
路人甲 say : count is 16
路人甲 say : count is 17
路人甲 say : count is 18
路人甲 say : count is 19
路人乙 say : count is 20
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通过日志可以看出,基本是线程甲在执行,这是因为sleep时,机锁一直在线程甲上,所以线程乙只能一直等待直到线程甲释放锁。
wait
1.wait()是Object类的一个方法。当调用wait()方法时,该线程会进入和该对象相关的等待池中,并释放它所拥有的机锁。
2.执行wait()后,必须使用notify()方法或notifyAll()方法或设置等待时间(wait(long time))唤醒在等待线程池中的线程。
3.wait()必须放在synchronized block中,否则会在运行时报“java.lang.IllegalMonitorStateException”异常
wait相关代码
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public class ThreadTest2 {
public static void main(String[] args) {
System.out.println( "begin our test" );
ThreadSleep sleep = new ThreadSleep();
try {
Thread thread1 = new Thread(sleep, "路人甲" );
Thread thread2 = new Thread(sleep, "路人乙" );
thread1.start();
thread2.start();
} catch (Exception e) {
e.printStackTrace();
}
System.out.println( "test is over" );
}
}
class ThreadSleep implements Runnable {
int count = 0 ;
@Override
public void run() {
System.out.println(Thread.currentThread().getName() + " say : hello sleep !!" );
count();
}
public void count() {
while (count < 20 ) {
synchronized ( this ) {
System.out.println(Thread.currentThread().getName() + " say : count is " + count);
try {
count++;
this .wait( 100 );
} catch (Exception e) {
e.printStackTrace();
}
}
}
}
}
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输出日志
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begin our test
路人甲 say : hello sleep !!
路人甲 say : count is 0
test is over
路人乙 say : hello sleep !!
路人乙 say : count is 1
路人甲 say : count is 2
路人乙 say : count is 3
路人甲 say : count is 4
路人乙 say : count is 5
路人甲 say : count is 6
路人乙 say : count is 7
路人甲 say : count is 8
路人乙 say : count is 9
路人甲 say : count is 10
路人乙 say : count is 11
路人甲 say : count is 12
路人乙 say : count is 13
路人乙 say : count is 14
路人甲 say : count is 15
路人乙 say : count is 16
路人甲 say : count is 17
路人乙 say : count is 18
路人甲 say : count is 19
|
通过日志可以发现在wait的情况下,机锁会被释放。
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原文链接:https://my.oschina.net/u/241670/blog/842172