java ReentrantLock

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介绍

ReentrantLock称为重入锁,比内部锁synchonized拥有更强大的功能,它可中断、可定时、设置公平锁

【注】使用ReentrantLock时,一定要释放锁,一般释放放到finnal里写。

提供以下重要的方法

lock():获得锁,如果锁已被占用,则等待

lockInterruptibly():获得锁,但有限响应中断

unlock():释放锁

tryLock():尝试获取锁。如果获得,返回true;否则返回false

tryLock(long time, TimeUnit unit):在给定时间内获得锁。如果获得返回true;否则返回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\");
    }
}

一次执行结果:

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执行,secondThread不停的判断是否可以获得锁,当firstThread执行完,secondThread执行后被打断

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\");
    }
}

一次执行结果

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执行,secondThread等待,等待过程被打断。打断后firstThread执行结束了,secondThread得到锁,继续执行

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\");
    }
}

一次执行结果

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先获得锁执行,secondThread在等待,此时中断并未打断等待。firstThread执行完,secondThread获取后被打断

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\");
    }
}

一次执行结果

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();在执行过程中可以响应中断时间

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