synchronized與Lock的區別

時間 2019-11-16

標籤 synchronized lock 區別欄目 Java 简体版

原文原文鏈接

二者區別：java

1.首先synchronized是java內置關鍵字，在jvm層面，Lock是個java類；jvm

2.synchronized沒法判斷是否獲取鎖的狀態，Lock能夠判斷是否獲取到鎖；ide

3.synchronized會自動釋放鎖(a 線程執行完同步代碼會釋放鎖；b 線程執行過程當中發生異常會釋放鎖)，Lock需在finally中手工釋放鎖（unlock()方法釋放鎖），不然容易形成線程死鎖；spa

4.用synchronized關鍵字的兩個線程1和線程2，若是當前線程1得到鎖，線程2線程等待。若是線程1阻塞，線程2則會一直等待下去，而Lock鎖就不必定會等待下去，若是嘗試獲取不到鎖，線程能夠不用一直等待就結束了；線程

5.synchronized的鎖可重入、不可中斷、非公平，而Lock鎖可重入、可判斷、可公平（二者皆可）3d

6.Lock鎖適合大量同步的代碼的同步問題，synchronized鎖適合代碼少許的同步問題。code

小例子：blog

package com.cn.test.thread.lock;
 
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
 
public class LockTest {
    private Lock lock = new ReentrantLock();
    /*
     * 使用完畢釋放後其餘線程才能獲取鎖
     */
    public void lockTest(Thread thread) {
        lock.lock();//獲取鎖
        try {
            System.out.println("線程"+thread.getName() + "獲取當前鎖"); //打印當前鎖的名稱
            Thread.sleep(2000);//爲看出執行效果，是線程此處休眠2秒
        } catch (Exception e) {
            System.out.println("線程"+thread.getName() + "發生了異常釋放鎖");
        }finally {
            System.out.println("線程"+thread.getName() + "執行完畢釋放鎖");
            lock.unlock(); //釋放鎖
        }
    }
     
    public static void main(String[] args) {
        LockTest lockTest = new LockTest();
        //聲明一個線程 「線程一」
        Thread thread1 = new Thread(new Runnable() {
            @Override
            public void run() {
                lockTest.lockTest(Thread.currentThread());
            }
        }, "thread1");
        //聲明一個線程 「線程二」
        Thread thread2 = new Thread(new Runnable() {
 
            @Override
            public void run() {
                lockTest.lockTest(Thread.currentThread());
            }
        }, "thread2");
        // 啓動2個線程
        thread2.start();
        thread1.start();
 
    }
}

執行結果：get

package com.cn.test.thread.lock;

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

public class LockTest {
    private Lock lock = new ReentrantLock();
    
    /*
     * 嘗試獲取鎖 tryLock() 它表示用來嘗試獲取鎖，若是獲取成功，則返回true，若是獲取失敗（即鎖已被其餘線程獲取），則返回false
     */
    public void tryLockTest(Thread thread) {
        if(lock.tryLock()) { //嘗試獲取鎖
            try {
                System.out.println("線程"+thread.getName() + "獲取當前鎖"); //打印當前鎖的名稱
                Thread.sleep(2000);//爲看出執行效果，是線程此處休眠2秒
            } catch (Exception e) {
                System.out.println("線程"+thread.getName() + "發生了異常釋放鎖");
            }finally {
                System.out.println("線程"+thread.getName() + "執行完畢釋放鎖");
                lock.unlock(); //釋放鎖
            }
        }else{
            System.out.println("我是線程"+Thread.currentThread().getName()+"當前鎖被別人佔用，我沒法獲取");
        }
    }
    public static void main(String[] args) {
        LockTest lockTest = new LockTest();
        
        Thread thread1 = new Thread(new Runnable() {
            @Override
            public void run() {
                lockTest.tryLockTest(Thread.currentThread());
            }
        }, "thread1");
        //聲明一個線程 「線程二」
        Thread thread2 = new Thread(new Runnable() {

            @Override
            public void run() {
                lockTest.tryLockTest(Thread.currentThread());
            }
        }, "thread2");
        // 啓動2個線程
        thread2.start();
        thread1.start();


    }
}

執行結果：同步

package com.cn.test.thread.lock;

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

public class LockTest {
    private Lock lock = new ReentrantLock();
    public void tryLockParamTest(Thread thread) throws InterruptedException {
        if(lock.tryLock(3000, TimeUnit.MILLISECONDS)) { //嘗試獲取鎖 獲取不到鎖，就等3秒，若是3秒後仍是獲取不到就返回false  
            try {
                System.out.println("線程"+thread.getName() + "獲取當前鎖"); //打印當前鎖的名稱
                Thread.sleep(4000);//爲看出執行效果，是線程此處休眠2秒
            } catch (Exception e) {
                System.out.println("線程"+thread.getName() + "發生了異常釋放鎖");
            }finally {
                System.out.println("線程"+thread.getName() + "執行完畢釋放鎖");
                lock.unlock(); //釋放鎖
            }
        }else{
            System.out.println("我是線程"+Thread.currentThread().getName()+"當前鎖被別人佔用,等待3s後仍沒法獲取,放棄");
        }
    }
    public static void main(String[] args) {
        LockTest lockTest = new LockTest();
        Thread thread1 = new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    lockTest.tryLockParamTest(Thread.currentThread());
                } catch (InterruptedException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
        }, "thread1");
        //聲明一個線程 「線程二」
        Thread thread2 = new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    lockTest.tryLockParamTest(Thread.currentThread());
                } catch (InterruptedException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
        }, "thread2");
        // 啓動2個線程
        thread2.start();
        thread1.start();
    }
}