在java多線程中，我們知道可以用synchronize關鍵字來實現線程間的同步互斥工作，還有更加優秀的機制去實現同步互斥工作，Lock對象。重入鎖和讀寫鎖，他們具有比synchronize更加強大的功能，並且具有嗅探鎖定，多路分支等功能。
一、ReentrantLock（重入鎖）（詳見JDK-API）
public class UseReentrantLock {
private Lock lock = new ReentrantLock();
public void method1(){
try {
lock.lock();
System.out.println("當前線程:" + Thread.currentThread().getName() + "進入method1..");
Thread.sleep(1000);
System.out.println("當前線程:" + Thread.currentThread().getName() + "退出method1..");
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
} finally {
lock.unlock();
}
}
public void method2(){
try {
lock.lock();
System.out.println("當前線程:" + Thread.currentThread().getName() + "進入method2..");
Thread.sleep(2000);
System.out.println("當前線程:" + Thread.currentThread().getName() + "退出method2..");
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
} finally {
lock.unlock();
}
}
public static void main(String[] args) {
final UseReentrantLock ur = new UseReentrantLock();
Thread t1 = new Thread(new Runnable() {
@Override
public void run() {
ur.method1();
ur.method2();
}
}, "t1");
t1.start();
try {
Thread.sleep(10);
} catch (InterruptedException e) {
e.printStackTrace();
}
//System.out.println(ur.lock.getQueueLength());
}
}
二、鎖的等待與通知
在使用synchronize的時候，如果需要多線程之間進行協作工作，則需要Object的wait（）和notify（）,notifyAll( )方法進行配合工作。那麼同樣，我們在使用Lock的時候，可以使用一個新的等待通知類，它就是Condition，這個Condition一定是針對具體某一把鎖的。也就是在只有鎖的基礎上纔會產生Condition。
public class UseCondition {
private Lock lock = new ReentrantLock();
private Condition condition = lock.newCondition();
public void method1(){
try {
lock.lock();
System.out.println("當前線程：" + Thread.currentThread().getName() + "進入等待狀態..");
Thread.sleep(3000);
System.out.println("當前線程：" + Thread.currentThread().getName() + "釋放鎖..");
condition.await(); // Object wait
System.out.println("當前線程：" + Thread.currentThread().getName() +"繼續執行...");
} catch (Exception e) {
e.printStackTrace();
} finally {
lock.unlock();
}
}
public void method2(){
try {
lock.lock();
System.out.println("當前線程：" + Thread.currentThread().getName() + "進入..");
Thread.sleep(3000);
System.out.println("當前線程：" + Thread.currentThread().getName() + "發出喚醒..");
condition.signal(); //Object notify
} catch (Exception e) {
e.printStackTrace();
} finally {
lock.unlock();
}
}
public static void main(String[] args) {
final UseCondition uc = new UseCondition();
Thread t1 = new Thread(new Runnable() {
@Override
public void run() {
uc.method1();
}
}, "t1");
Thread t2 = new Thread(new Runnable() {
@Override
public void run() {
uc.method2();
}
}, "t2");
t1.start();
t2.start();
}
}
三、多Condition
我們可以通過一個Lock對象產生多個Condition進行多線程間的交互，非常的靈活。可以使得部分需要喚醒的線程喚醒，其他線程則繼續等待通知。
public class UseManyCondition {
private ReentrantLock lock = new ReentrantLock();
private Condition c1 = lock.newCondition();
private Condition c2 = lock.newCondition();
public void m1(){
try {
lock.lock();
System.out.println("當前線程：" +Thread.currentThread().getName() + "進入方法m1等待..");
c1.await();
System.out.println("當前線程：" +Thread.currentThread().getName() + "方法m1繼續..");
} catch (Exception e) {
e.printStackTrace();
} finally {
lock.unlock();
}
}
public void m2(){
try {
lock.lock();
System.out.println("當前線程：" +Thread.currentThread().getName() + "進入方法m2等待..");
c1.await();
System.out.println("當前線程：" +Thread.currentThread().getName() + "方法m2繼續..");
} catch (Exception e) {
e.printStackTrace();
} finally {
lock.unlock();
}
}
public void m3(){
try {
lock.lock();
System.out.println("當前線程：" +Thread.currentThread().getName() + "進入方法m3等待..");
c2.await();
System.out.println("當前線程：" +Thread.currentThread().getName() + "方法m3繼續..");
} catch (Exception e) {
e.printStackTrace();
} finally {
lock.unlock();
}
}
public void m4(){
try {
lock.lock();
System.out.println("當前線程：" +Thread.currentThread().getName() + "喚醒..");
c1.signalAll();
} catch (Exception e) {
e.printStackTrace();
} finally {
lock.unlock();
}
}
public void m5(){
try {
lock.lock();
System.out.println("當前線程：" +Thread.currentThread().getName() + "喚醒..");
c2.signal();
} catch (Exception e) {
e.printStackTrace();
} finally {
lock.unlock();
}
}
public static void main(String[] args) {
final UseManyCondition umc = new UseManyCondition();
Thread t1 = new Thread(new Runnable() {
@Override
public void run() {
umc.m1();
}
},"t1");
Thread t2 = new Thread(new Runnable() {
@Override
public void run() {
umc.m2();
}
},"t2");
Thread t3 = new Thread(new Runnable() {
@Override
public void run() {
umc.m3();
}
},"t3");
Thread t4 = new Thread(new Runnable() {
@Override
public void run() {
umc.m4();
}
},"t4");
Thread t5 = new Thread(new Runnable() {
@Override
public void run() {
umc.m5();
}
},"t5");
t1.start(); // c1
t2.start(); // c1
t3.start(); // c2
try {
Thread.sleep(2000);
} catch (InterruptedException e) {
e.printStackTrace();
}
t4.start(); // c1
try {
Thread.sleep(2000);
} catch (InterruptedException e) {
e.printStackTrace();
}
t5.start(); // c2
}
四 . Lock / Condition其他方法和用法
1.公平鎖和非公平鎖: Lock lock = new ReentrantLock ( boolean isFair);
lock的用法:
tryLock():嘗試獲得鎖,獲得結果用true/false返回.
tryLock():在給定的時間內嘗試獲得鎖,獲得結果用true/false返回.
isFair():是否是公平鎖
isLocked():是否鎖定
getHoldCount():查詢當前線程保持此鎖的個數,也就是調用lock()的次數
lockInterruptibly:優先響應中斷的鎖