Java中如何避免死锁呢?
下文笔者讲述java中避免死锁的方法分享,如下所示
使用信号量控制死锁
避免死锁的方法: 不使用synchronized这个显式的锁,而采用信号量控制资源,可被多少线程访问 当设置资源只可被一个线程访问时,则此时为锁住状态, 信号量可设置获取的超时时间, 对无法成功获取,可进行重复尝试,或指定尝试次数后,也可立即退出例:
使用信号量控制死锁
package com.java265.other; import java.util.Date; import java.util.concurrent.Semaphore; import java.util.concurrent.TimeUnit; public class Test16 { public static String obj1 = "java265.com-1"; public static final Semaphore a1 = new Semaphore(1); public static String obj2 = "java265.com-2"; public static final Semaphore a2 = new Semaphore(1); public static void main(String[] args) { LockAa a = new LockAa(); new Thread(a).start(); LockBb b = new LockBb(); new Thread(b).start(); } } class LockAa implements Runnable { public void run() { try { System.out.println(new Date().toString() + " LockA 开始执行"); while (true) { if (Test16.a1.tryAcquire(1, TimeUnit.SECONDS)) { System.out.println(new Date().toString() + " LockA 锁住 obj1"); if (Test16.a2.tryAcquire(1, TimeUnit.SECONDS)) { System.out.println(new Date().toString() + " LockA 锁住 obj2"); Thread.sleep(60 * 1000); // do something } else { System.out.println(new Date().toString() + "LockA 锁 obj2 失败"); } } else { System.out.println(new Date().toString() + "LockA 锁 obj1 失败"); } Test16.a1.release(); // 释放 Test16.a2.release(); Thread.sleep(1000); // 马上进行尝试,现实情况下do something是不确定的 } } catch (Exception e) { e.printStackTrace(); } } } class LockBb implements Runnable { public void run() { try { System.out.println("java265.com " + new Date().toString() + " LockB 开始执行"); while (true) { if (Test16.a2.tryAcquire(1, TimeUnit.SECONDS)) { System.out.println(new Date().toString() + " LockB 锁住 obj2"); if (Test16.a1.tryAcquire(1, TimeUnit.SECONDS)) { System.out.println(new Date().toString() + " LockB 锁住 obj1"); Thread.sleep(60 * 1000); // do something } else { System.out.println(new Date().toString() + "LockB 锁 obj1 失败"); } } else { System.out.println(new Date().toString() + "LockB 锁 obj2 失败"); } Test16.a1.release(); // 释放 Test16.a2.release(); Thread.sleep(10 * 1000); // 这里只是为了演示,所以tryAcquire只用1秒,而且B要给A让出能执行的时间,否则两个永远是死锁 } } catch (Exception e) { e.printStackTrace(); } } } -----运行以上代码,将输出以下信息----- Thu Apr 28 23:01:32 CST 2022 LockA 开始执行 java265.com Thu Apr 28 23:01:32 CST 2022 LockB 开始执行 Thu Apr 28 23:01:32 CST 2022 LockA 锁住 obj1 Thu Apr 28 23:01:32 CST 2022 LockB 锁住 obj2 Thu Apr 28 23:01:33 CST 2022LockB 锁 obj1 失败 Thu Apr 28 23:01:33 CST 2022LockA 锁 obj2 失败 Thu Apr 28 23:01:34 CST 2022 LockA 锁住 obj1 Thu Apr 28 23:01:34 CST 2022 LockA 锁住 obj2 Thu Apr 28 23:01:43 CST 2022 LockB 锁住 obj2 Thu Apr 28 23:01:43 CST 2022 LockB 锁住 obj1 Thu Apr 28 23:02:35 CST 2022 LockA 锁住 obj1 Thu Apr 28 23:02:35 CST 2022 LockA 锁住 obj2
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