使用Lock物件實現同步效果
阿新 • • 發佈：2018-12-29
Lock是一個介面，為了使用一個Lock物件，需要用到
Lock lock = new ReentrantLock();與 synchronized (someObject) 類似的，lock()方法，表示當前執行緒佔用lock物件，一旦佔用，其他執行緒就不能佔用了。
與 synchronized 不同的是，一旦synchronized 塊結束，就會自動釋放對someObject的佔用。 lock卻必須呼叫unlock方法進行手動釋放，為了保證釋放的執行，往往會把unlock() 放在finally中進行。
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package
multiplethread;
import
java.text.SimpleDateFormat;
import
java.util.Date;import
java.util.concurrent.locks.Lock;
import
java.util.concurrent.locks.ReentrantLock;
public
class
TestThread {
public
static
String now() {
return
new
SimpleDateFormat(
"HH:mm:ss"
).format(
new
Date());
}
public
static
void
log(String msg) {
System.out.printf(
"%s %s %s %n"
, now() , Thread.currentThread().getName() , msg);
}
public
static
void
main(String[] args) {
Lock lock =
new
ReentrantLock();
Thread t1 =
new
Thread() {
public
void
run() {
try
{
log(
"執行緒啟動"
);
log(
"試圖佔有物件：lock"
);
lock.lock();
log(
"佔有物件：lock"
);
log(
"進行5秒的業務操作"
);
Thread.sleep(
5000
);
}
catch
(InterruptedException e) {
e.printStackTrace();
}
finally
{
log(
"釋放物件：lock"
);
lock.unlock();
}
log(
"執行緒結束"
);
}
};
t1.setName(
"t1"
);
t1.start();
try
{
//先讓t1飛2秒
Thread.sleep(
2000
);
}
catch
(InterruptedException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
}
Thread t2 =
new
Thread() {
public
void
run() {
try
{
log(
"執行緒啟動"
);
log(
"試圖佔有物件：lock"
);
lock.lock();
log(
"佔有物件：lock"
);
log(
"進行5秒的業務操作"
);
Thread.sleep(
5000
);
}
catch
(InterruptedException e) {
e.printStackTrace();
}
finally
{
log(
"釋放物件：lock"
);
lock.unlock();
}
log(
"執行緒結束"
);
}
};
t2.setName(
"t2"
);
t2.start();
}
}
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