tryLock(long time, TimeUnit unit) 的作用在給定等待時長內鎖沒有被另外的線程持有，并且當前線程也沒有被中斷,則獲得該鎖，通過該方法可以實現鎖對象的限時等待。
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package com.wkcto.lock.reentrant;import java.util.concurrent.TimeUnit;import java.util.concurrent.locks.ReentrantLock;/** *tryLock(long time, TimeUnit unit) 的基本使用 */public class Test07 { static class TimeLock implements Runnable{ private static ReentrantLock lock = new ReentrantLock(); //定義鎖對象 @Override public void run() { try { if ( lock.tryLock(3, TimeUnit.SECONDS) ){ //獲得鎖返回true System.out.println(Thread.currentThread().getName() + "獲得鎖,執行耗時任務");// Thread.sleep(4000); //假設Thread-0線程先持有鎖,完成任務需要4秒鐘,Thread-1線程嘗試獲得鎖,Thread-1線程在3秒內還沒有獲得鎖的話,Thread-1線程會放棄 Thread.sleep(2000); //假設Thread-0線程先持有鎖,完成任務需要2秒鐘,Thread-1線程嘗試獲得鎖,Thread-1線程會一直嘗試,在它約定嘗試的3秒內可以獲得鎖對象 }else { //沒有獲得鎖 System.out.println(Thread.currentThread().getName() + "沒有獲得鎖"); } } catch (InterruptedException e) { e.printStackTrace(); } finally { if (lock.isHeldByCurrentThread()){ lock.unlock(); } } } } public static void main(String[] args) { TimeLock timeLock = new TimeLock(); Thread t1 = new Thread(timeLock); Thread t2 = new Thread(timeLock); t1.start(); t2.start(); }} |
tryLock()僅在調用時鎖定未被其他線程持有的鎖，如果調用方法時，鎖對象對其他線程持有，則放棄，調用方法嘗試獲得沒，如果該鎖沒有被其他線程占用則返回true表示鎖定成功; 如果鎖被其他線程占用則返回false,不等待。
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package com.wkcto.lock.reentrant;import java.util.concurrent.locks.ReentrantLock;/** *tryLock() * 當鎖對象沒有被其他線程持有的情況下才會獲得該鎖定 */public class Test08 { static class Service{ private ReentrantLock lock = new ReentrantLock(); public void serviceMethod(){ try { if (lock.tryLock()){ System.out.println(Thread.currentThread().getName() + "獲得鎖定"); Thread.sleep(3000); //模擬執行任務的時長 }else { System.out.println(Thread.currentThread().getName() + "沒有獲得鎖定"); } } catch (InterruptedException e) { e.printStackTrace(); } finally { if (lock.isHeldByCurrentThread()){ lock.unlock(); } } } } public static void main(String[] args) throws InterruptedException { Service service = new Service(); Runnable r = new Runnable() { @Override public void run() { service.serviceMethod(); } }; Thread t1 = new Thread(r); t1.start(); Thread.sleep(50); //睡眠50毫秒,確保t1線程鎖定 Thread t2 = new Thread(r); t2.start(); }} |
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package com.wkcto.lock.reentrant;import java.util.Random;import java.util.concurrent.locks.ReentrantLock;/** * 使用tryLock()可以避免死鎖 */public class Test09 { static class IntLock implements Runnable{ private static ReentrantLock lock1 = new ReentrantLock(); private static ReentrantLock lock2 = new ReentrantLock(); private int lockNum; //用于控制鎖的順序 public IntLock(int lockNum) { this.lockNum = lockNum; } @Override public void run() { if ( lockNum % 2 == 0 ){ //偶數先鎖1,再鎖2 while (true){ try { if (lock1.tryLock()){ System.out.println(Thread.currentThread().getName() + "獲得鎖1, 還想獲得鎖2"); Thread.sleep(new Random().nextInt(100)); try { if (lock2.tryLock()){ System.out.println(Thread.currentThread().getName() + "同時獲得鎖1與鎖2 ----完成任務了"); return; //結束run()方法執行,即當前線程結束 } } finally { if (lock2.isHeldByCurrentThread()){ lock2.unlock(); } } } } catch (InterruptedException e) { e.printStackTrace(); } finally { if (lock1.isHeldByCurrentThread()){ lock1.unlock(); } } } }else { //奇數就先鎖2,再鎖1 while (true){ try { if (lock2.tryLock()){ System.out.println(Thread.currentThread().getName() + "獲得鎖2, 還想獲得鎖1"); Thread.sleep(new Random().nextInt(100)); try { if (lock1.tryLock()){ System.out.println(Thread.currentThread().getName() + "同時獲得鎖1與鎖2 ----完成任務了"); return; //結束run()方法執行,即當前線程結束 } } finally { if (lock1.isHeldByCurrentThread()){ lock1.unlock(); } } } } catch (InterruptedException e) { e.printStackTrace(); } finally { if (lock2.isHeldByCurrentThread()){ lock2.unlock(); } } } } } } public static void main(String[] args) { IntLock intLock1 = new IntLock(11); IntLock intLock2 = new IntLock(22); Thread t1 = new Thread(intLock1); Thread t2 = new Thread(intLock2); t1.start(); t2.start(); //運行后,使用tryLock()嘗試獲得鎖,不會傻傻的等待,通過循環不停的再次嘗試,如果等待的時間足夠長,線程總是會獲得想要的資源 }} |
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原文鏈接：https://juejin.cn/post/7023267765918105630
