Java 同步代码块 - Synchronized Blocks

java锁实现原理：

http://blog.csdn.net/endlu/article/details/51249156

The synchronized keyword can be used to mark four different types of blocks:

Instance methods
Static methods
Code blocks inside instance methods
Code blocks inside static methods

Instance methods & Code blocks inside instance methods

Java实例方法同步是同步在拥有该方法的对象上

同步构造器中用括号括起来的对象叫做监视器对象

public class SyncBlockTest {

    public static void main(String[] args) {

        ExecutorService es = Executors.newFixedThreadPool(2);

        final MySyncBlockClass syncBlockClass = new MySyncBlockClass();

        es.submit(new Runnable() {

            @Override

            public void run() {

                try {

                    syncBlockClass.mehtod1();

                } catch (InterruptedException e) {

                    e.printStackTrace();

                }

            }

        });

        es.submit(new Runnable() {

            @Override

            public void run() {

                try {

                    syncBlockClass.mehtod2();

                } catch (InterruptedException e) {

                    e.printStackTrace();

                }

            }

        });

        es.shutdown();

    }

}

class MySyncBlockClass {

    public synchronized void mehtod1() throws InterruptedException {

        TimeUnit.SECONDS.sleep(1);

        System.out.println(System.currentTimeMillis() + ":method1 run.");

    }

    public synchronized void mehtod2() throws InterruptedException {

        TimeUnit.SECONDS.sleep(4);

        System.out.println(System.currentTimeMillis() + ":method2 run.");

    }

}

// method1较method2延迟了2000ms

// 1479350064132:method2 run.

// 1479350066132:method1 run.

实例方法同步

/**

     * method1 与method2等效

     * 同步构造器中用括号括起来的对象叫做监视器对象

     *

     * @throws InterruptedException

     */

    public synchronized void mehtod1() throws InterruptedException {

        TimeUnit.SECONDS.sleep(1);

        System.out.println(System.currentTimeMillis() + ":method1 run.");

    }

    public synchronized void mehtod2() throws InterruptedException {

        synchronized (this) {

            TimeUnit.SECONDS.sleep(4);

            System.out.println(System.currentTimeMillis() + ":method2 run.");

        }

    }

实例方法中的同步块

Static methods & Code blocks inside static methods

静态方法的同步是指同步在该方法所在的类对象上。因为在Java虚拟机中一个类只能对应一个类对象，所以同时只允许一个线程执行同一个类中的静态同步方法。

public class SyncBlockTest {

    public static void main(String[] args) {

        ExecutorService es = Executors.newFixedThreadPool(2);

        final MySyncBlockClass syncBlockClass1 = new MySyncBlockClass();

        final MySyncBlockClass syncBlockClass2 = new MySyncBlockClass();

        es.submit(new Runnable() {

            @Override

            public void run() {

                try {

                    syncBlockClass1.mehtod1();

                } catch (InterruptedException e) {

                    e.printStackTrace();

                }

            }

        });

        es.submit(new Runnable() {

            @Override

            public void run() {

                try {

                    syncBlockClass2.mehtod2();

                } catch (InterruptedException e) {

                    e.printStackTrace();

                }

            }

        });

        es.shutdown();

    }

}

class MySyncBlockClass {

    public static synchronized void mehtod1() throws InterruptedException {

        TimeUnit.SECONDS.sleep(1);

        System.out.println(System.currentTimeMillis() + ":method1 run.");

    }

    public static synchronized void mehtod2() throws InterruptedException {

        TimeUnit.SECONDS.sleep(4);

        System.out.println(System.currentTimeMillis() + ":method2 run.");

    }

}

// method1较method2延迟了3000ms

// 1479358310630:method1 run.

// 1479358314631:method2 run.

静态方法同步

/**

     * method1 与method2等效

     * 静态方法中的同步块

     *

     * @throws InterruptedException

     */

    public static synchronized void mehtod1() throws InterruptedException {

        TimeUnit.SECONDS.sleep(1);

        System.out.println(System.currentTimeMillis() + ":method1 run.");

    }

    public static synchronized void mehtod2() throws InterruptedException {

        synchronized (MySyncBlockClass.class) {

            TimeUnit.SECONDS.sleep(4);

            System.out.println(System.currentTimeMillis() + ":method2 run.");

        }

    }

静态方法中的同步块

示例：

以下代码对应的Block关系如下：

synchronized(class)与 static synchronized 等效

public class SyncMethod2 {

    private int value = 0;

    private final Object mutex = new Object();

    public synchronized int incAndGet0() {

        try {

            TimeUnit.SECONDS.sleep(4);

        } catch (InterruptedException e) {

            e.printStackTrace();

        }

        System.out.println("static synchronized void incAndGet0");

        return ++value;

    }

    public int incAndGet1() {

        synchronized(this){

            try {

                TimeUnit.SECONDS.sleep(4);

            } catch (InterruptedException e) {

                e.printStackTrace();

            }

            System.out.println("static synchronized void incAndGet1");

            return ++value;

        }

    }

    public int incAndGet2() {

        synchronized(SyncMethod.class){

            ++value;

            try {

                TimeUnit.SECONDS.sleep(4);

            } catch (InterruptedException e) {

                e.printStackTrace();

            }

            System.out.println("static synchronized void incAndGet4");

        }

        return 0;

    }

    public int incAndGet3() {

        synchronized(mutex){

            return ++value;

        }

    }

    public static synchronized void incAndGet4() {

        try {

            TimeUnit.SECONDS.sleep(4);

            System.out.println("static synchronized void incAndGet4");

        } catch (InterruptedException e) {

            e.printStackTrace();

        }

    }

}

各种同步场景

巴特西

Java 同步代码块 - Synchronized Blocks

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