程序如下：
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public
static
void
main(String[] args)
throws
Exception{
final
List list =
new
ArrayList();
final
Object lock =
new
Object();
Thread t1 =
new
Thread(
new
Runnable() {
@Override
public
void
run() {
synchronized
(lock){
for
(
int
i =
0
; i <
10
; i++){
list.add(i);
if
(list.size() ==
5
){
lock.notify();
System.out.println(Thread.currentThread().getName() +
"发出通知!"
);
}
}
}
System.out.println(Thread.currentThread().getName() +
"execute over!"
);
}
});
Thread t2 =
new
Thread(
new
Runnable() {
@Override
public
void
run() {
synchronized
(lock){
if
(list.size() !=
5
){
try
{
lock.wait();
}
catch
(InterruptedException e) {
e.printStackTrace();
}
}
System.out.println(Thread.currentThread().getName() +
" 收到通知!"
);
}
System.out.println(Thread.currentThread().getName() +
"execute over!"
);
}
});
t2.start();
Thread.sleep(
1000
);
t1.start();
}
|
分析：
程序的意图本是利用多线程之间的通信，利用wait/notify实现，可是运行的结果是虽然线程T1发出了通知，但是线程T2并没有立即收到通知进行执行，这是为什么呢？ 因为只有线程T1执行完毕释放了锁，T2才能执行，那么也就是说wait/notify并不是实时的（wait释放了锁，而notify没有释放锁导致的），那么线程之间实时的通信该怎么做呢？可以利用CountDownLatch来实现。
对程序的改进：
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public
static
void
main(String[] args)
throws
Exception{
final
List list =
new
ArrayList();
final
Object lock =
new
Object();
final
CountDownLatch countDownLatch =
new
CountDownLatch(
1
);
Thread t1 =
new
Thread(
new
Runnable() {
@Override
public
void
run() {
for
(
int
i =
0
; i <
10
; i++){
list.add(i);
if
(list.size() ==
5
){
countDownLatch.countDown();
System.out.println(Thread.currentThread().getName() +
"发出通知!"
);
}
}
System.out.println(Thread.currentThread().getName() +
"execute over!"
);
}
});
Thread t2 =
new
Thread(
new
Runnable() {
@Override
public
void
run() {
if
(list.size() !=
5
){
try
{
countDownLatch.await();
}
catch
(InterruptedException e) {
e.printStackTrace();
}
System.out.println(Thread.currentThread().getName() +
" 收到通知!"
);
}
System.out.println(Thread.currentThread().getName() +
"execute over!"
);
}
});
t2.start();
Thread.sleep(
1000
);
t1.start();
}
|
本文转自zfz_linux_boy 51CTO博客，原文链接：http://blog.51cto.com/zhangfengzhe/1875221，如需转载请自行联系原作者
