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java ReentrantLock

介紹

ReentrantLock稱為重入鎖，比内部鎖synchonized擁有更強大的功能，它可中斷、可定時、設定公平鎖

【注】使用ReentrantLock時，一定要釋放鎖，一般釋放放到finnal裡寫。

提供以下重要的方法

  • lock():獲得鎖，如果鎖已被占用，則等待
  • lockInterruptibly():獲得鎖，但有限響應中斷
  • unlock():釋放鎖
  • tryLock():嘗試擷取鎖。如果獲得，傳回true；否則傳回false
  • tryLock(long time, TimeUnit unit):在給定時間内獲得鎖。如果獲得傳回true；否則傳回false

示例

例子1

import java.util.concurrent.locks.ReentrantLock;

public class ReentrantLockTest {
    ReentrantLock lock;

    ReentrantLockTest(ReentrantLock lock) {
        this.lock = lock;
    }

    private Runnable getRunnable() {
        return new Runnable() {
            @Override
            public void run() {
                while(true) {
                    try {
                        if (lock.tryLock()) {
                            try {
                                System.out.println("Locked:" + Thread.currentThread().getName());
                                Thread.sleep(800);
                            } finally {
                                lock.unlock();
                                System.out.println("UnLocked:" + Thread.currentThread().getName());
                            }
                            System.out.println("break before");
                            break;
                        } else {
                            //System.out.println("Unable to lock " + Thread.currentThread().getName());
                        }

                    } catch (InterruptedException e){
                        System.out.println(Thread.currentThread() + " is Interupted");
                        e.printStackTrace();
                    }
                }
            }
        };
    }

    public static void main(String[] args) {
        ReentrantLock lock = new ReentrantLock();
        ReentrantLockTest test = new ReentrantLockTest(lock);
        ReentrantLockTest test2 = new ReentrantLockTest(lock);
        Thread thread1 = new Thread(test.getRunnable(), "firstThread");
        Thread thread2 = new Thread(test2.getRunnable(), "secondThread");

        thread1.start();
        thread2.start();
        try {
            Thread.sleep(300);
        }catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("interupt begin");
        thread2.interrupt();
        System.out.println("interupt end");
    }
}

一次執行結果：

Locked:firstThread
interupt begin
interupt end
UnLocked:firstThread
break before
Locked:secondThread
UnLocked:secondThread
Thread[secondThread,5,main] is Interupted
java.lang.InterruptedException: sleep interrupted
	at java.lang.Thread.sleep(Native Method)
	at com.jihite.templet.JavaBase.ReentrantLockTest$1.run(ReentrantLockTest.java:23)
	at java.lang.Thread.run(Thread.java:748)
Locked:secondThread
UnLocked:secondThread
break before

分析：firstThread執行，secondThread不停的判斷是否可以獲得鎖，當firstThread執行完，secondThread執行後被打斷

例子2

import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.ReentrantLock;

public class ReentrantLockTest {
    ReentrantLock lock;

    ReentrantLockTest(ReentrantLock lock) {
        this.lock = lock;
    }

    private Runnable getRunnable() {
        return new Runnable() {
            @Override
            public void run() {
                while(true) {
                    try {
                        if (lock.tryLock(700, TimeUnit.MILLISECONDS)) {
                            try {
                                System.out.println("Locked:" + Thread.currentThread().getName());
                                Thread.sleep(800);
                            } finally {
                                lock.unlock();
                                System.out.println("UnLocked:" + Thread.currentThread().getName());
                            }
                            System.out.println("break before");
                            break;
                        } else {
                            //System.out.println("Unable to lock " + Thread.currentThread().getName());
                        }

                    } catch (InterruptedException e){
                        System.out.println(Thread.currentThread() + " is Interupted");
                        e.printStackTrace();
                    }
                }
            }
        };
    }

    public static void main(String[] args) {
        ReentrantLock lock = new ReentrantLock();
        ReentrantLockTest test = new ReentrantLockTest(lock);
        ReentrantLockTest test2 = new ReentrantLockTest(lock);
        Thread thread1 = new Thread(test.getRunnable(), "firstThread");
        Thread thread2 = new Thread(test2.getRunnable(), "secondThread");

        thread1.start();
        thread2.start();
        try {
            Thread.sleep(300);
        }catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("interupt begin");
        thread2.interrupt();
        System.out.println("interupt end");
    }
}

一次執行結果

Locked:firstThread
interupt begin
interupt end
Thread[secondThread,5,main] is Interupted
java.lang.InterruptedException
	at java.util.concurrent.locks.AbstractQueuedSynchronizer.doAcquireNanos(AbstractQueuedSynchronizer.java:936)
	at java.util.concurrent.locks.AbstractQueuedSynchronizer.tryAcquireNanos(AbstractQueuedSynchronizer.java:1247)
	at java.util.concurrent.locks.ReentrantLock.tryLock(ReentrantLock.java:442)
	at com.jihite.templet.JavaBase.ReentrantLockTest$1.run(ReentrantLockTest.java:19)
	at java.lang.Thread.run(Thread.java:748)
Locked:secondThread
UnLocked:firstThread
break before
UnLocked:secondThread
break before

分析：firstThread執行，secondThread等待，等待過程被打斷。打斷後firstThread執行結束了，secondThread得到鎖，繼續執行

例子3

import java.util.concurrent.locks.ReentrantLock;

public class ReentrantLockTest2 {
    ReentrantLock lock;

    ReentrantLockTest2(ReentrantLock lock) {
        this.lock = lock;
    }

    private Runnable getRunnable() {
        return new Runnable() {
            @Override
            public void run() {
                while (true) {
                    try {
                        try {
                            lock.lock();
//                            lock.lockInterruptibly();
                            System.out.println("Locked:" + Thread.currentThread().getName());
                            Thread.sleep(800);
                            break;
                        } finally {
                            lock.unlock();
                            System.out.println("UnLocked:" + Thread.currentThread().getName());
                        }
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            }
        };
    }

    public static void main(String[] args) {
        ReentrantLock lock = new ReentrantLock();
        ReentrantLockTest2 test = new ReentrantLockTest2(lock);
        ReentrantLockTest2 test2 = new ReentrantLockTest2(lock);
        Thread thread1 = new Thread(test.getRunnable(), "firstThread");
        Thread thread2 = new Thread(test2.getRunnable(), "secondThread");

        thread1.start();
        thread2.start();
        try {
            Thread.sleep(600);
        }catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("interupt begin");
        thread2.interrupt();
        System.out.println("interupt end");
    }
}      
Locked:firstThread
interupt begin
interupt end
UnLocked:firstThread
Locked:secondThread
UnLocked:secondThread
java.lang.InterruptedException: sleep interrupted
	at java.lang.Thread.sleep(Native Method)
	at com.jihite.templet.JavaBase.ReentrantLockTest2$1.run(ReentrantLockTest2.java:22)
	at java.lang.Thread.run(Thread.java:748)
Locked:secondThread
UnLocked:secondThread

分析：firstThread先獲得鎖執行，secondThread在等待，此時中斷并未打斷等待。firstThread執行完，secondThread擷取後被打斷

例子4

public class ReentrantLockTest2 {
    ReentrantLock lock;

    ReentrantLockTest2(ReentrantLock lock) {
        this.lock = lock;
    }

    private Runnable getRunnable() {
        return new Runnable() {
            @Override
            public void run() {
                while (true) {
                    try {
                        try {
//                            lock.lock();
                            lock.lockInterruptibly();
                            System.out.println("Locked:" + Thread.currentThread().getName());
                            Thread.sleep(800);
                            break;
                        } finally {
                            lock.unlock();
                            System.out.println("UnLocked:" + Thread.currentThread().getName());
                        }
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            }
        };
    }

    public static void main(String[] args) {
        ReentrantLock lock = new ReentrantLock();
        ReentrantLockTest2 test = new ReentrantLockTest2(lock);
        ReentrantLockTest2 test2 = new ReentrantLockTest2(lock);
        Thread thread1 = new Thread(test.getRunnable(), "firstThread");
        Thread thread2 = new Thread(test2.getRunnable(), "secondThread");

        thread1.start();
        thread2.start();
        try {
            Thread.sleep(600);
        }catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("interupt begin");
        thread2.interrupt();
        System.out.println("interupt end");
    }
}      
Locked:firstThread
interupt begin
interupt end
Exception in thread "secondThread" java.lang.IllegalMonitorStateException
	at java.util.concurrent.locks.ReentrantLock$Sync.tryRelease(ReentrantLock.java:151)
	at java.util.concurrent.locks.AbstractQueuedSynchronizer.release(AbstractQueuedSynchronizer.java:1261)
	at java.util.concurrent.locks.ReentrantLock.unlock(ReentrantLock.java:457)
	at com.jihite.templet.JavaBase.ReentrantLockTest2$1.run(ReentrantLockTest2.java:25)
	at java.lang.Thread.run(Thread.java:748)

分析：lock.lockInterruptibly();在執行過程中可以響應中斷時間

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