synchronized 用法详解
1. 加在普通方法上
单例下互斥，非单例无用
1 public class Test { 2 3 private synchronized void syncMethod1() { 4 System.out.println("in1：" + System.currentTimeMillis() / 1000); 5 try { 6 Thread.sleep(5000); 7 } catch (InterruptedException e) { 8 e.printStackTrace(); 9 } 10 } 11 12 private synchronized void syncMethod2() { 13 System.out.println("in2：" + System.currentTimeMillis() / 1000); 14 try { 15 Thread.sleep(5000); 16 } catch (InterruptedException e) { 17 e.printStackTrace(); 18 } 19 } 20 21 public static void main(String[] args) { 22 final Test test = new Test(); 23 new Thread(new Runnable() { 24 public void run() { 25 test.syncMethod1(); 26 } 27 }).start(); 28 29 new Thread(new Runnable() { 30 public void run() { 31 test.syncMethod2(); 32 } 33 }).start(); 34 35 } 36 }
result in1：1562051336 in2：1562051341
2.代码块，使用this
锁住当前对象，同上普通方法锁相同，非单例无用
1 public class Test { 2 3 4 private void syncMethod1() { 5 synchronized (this) { 6 System.out.println("in1：" + System.currentTimeMillis() / 1000); 7 try { 8 Thread.sleep(5000); 9 } catch (InterruptedException e) { 10 e.printStackTrace(); 11 } 12 } 13 14 } 15 16 private void syncMethod2() { 17 synchronized (this) { 18 System.out.println("in2：" + System.currentTimeMillis() / 1000); 19 try { 20 Thread.sleep(5000); 21 } catch (InterruptedException e) { 22 e.printStackTrace(); 23 } 24 } 25 } 26 27 public static void main(String[] args) { 28 final Test test = new Test(); 29 new Thread(new Runnable() { 30 public void run() { 31 test.syncMethod1(); 32 } 33 }).start(); 34 35 new Thread(new Runnable() { 36 public void run() { 37 test.syncMethod2(); 38 } 39 }).start(); 40 } 41 }
result in1：1562051825 in2：1562051830
3.加在静态方法
同类下互斥,非同类下无用
1 public class Test { 2 3 4 private static synchronized void syncMethod1() { 5 System.out.println("in1：" + System.currentTimeMillis() / 1000); 6 try { 7 Thread.sleep(5000); 8 } catch (InterruptedException e) { 9 e.printStackTrace(); 10 } 11 } 12 13 private static synchronized void syncMethod2() { 14 System.out.println("in2：" + System.currentTimeMillis() / 1000); 15 try { 16 Thread.sleep(5000); 17 } catch (InterruptedException e) { 18 e.printStackTrace(); 19 } 20 } 21 22 public static void main(String[] args) { 23 new Thread(new Runnable() { 24 public void run() { 25 Test.syncMethod1(); 26 } 27 }).start(); 28 29 new Thread(new Runnable() { 30 public void run() { 31 Test.syncMethod2(); 32 } 33 }).start(); 34 35 } 36 }
resut in1：1562051498 in2：1562051503
4.代码块，使用类
使用相同类名互斥，类级别锁，同静态类方法锁，多实例下有效
1 public class Test { 2 3 4 private void syncMethod1() { 5 synchronized (Test.class) { 6 System.out.println("in1：" + System.currentTimeMillis() / 1000); 7 try { 8 Thread.sleep(5000); 9 } catch (InterruptedException e) { 10 e.printStackTrace(); 11 } 12 } 13 14 } 15 16 private void syncMethod2() { 17 synchronized (Test.class) { 18 System.out.println("in2：" + System.currentTimeMillis() / 1000); 19 try { 20 Thread.sleep(5000); 21 } catch (InterruptedException e) { 22 e.printStackTrace(); 23 } 24 } 25 } 26 27 public static void main(String[] args) { 28 29 new Thread(new Runnable() { 30 public void run() { 31 new Test().syncMethod1(); 32 } 33 }).start(); 34 35 new Thread(new Runnable() { 36 public void run() { 37 new Test().syncMethod2(); 38 } 39 }).start(); 40 41 }
result in1：1562051647 in2：1562051652
5.自定义对象锁(非静态)
实例变量对象锁，单例有效，多例无用
1 public class Test { 2 3 private final String[] MY_LOCK = new String[]{}; 4 5 private void syncMethod1() { 6 synchronized (MY_LOCK) { 7 System.out.println("in1：" + System.currentTimeMillis() / 1000); 8 try { 9 Thread.sleep(5000); 10 } catch (InterruptedException e) { 11 e.printStackTrace(); 12 } 13 } 14 15 } 16 17 private void syncMethod2() { 18 synchronized (MY_LOCK) { 19 System.out.println("in2：" + System.currentTimeMillis() / 1000); 20 try { 21 Thread.sleep(5000); 22 } catch (InterruptedException e) { 23 e.printStackTrace(); 24 } 25 } 26 } 27 28 public static void main(String[] args) { 29 final Test test = new Test(); 30 new Thread(new Runnable() { 31 public void run() { 32 test.syncMethod1(); 33 } 34 }).start(); 35 36 new Thread(new Runnable() { 37 public void run() { 38 test.syncMethod2(); 39 } 40 }).start(); 41 } 42 }
result in1：1562052198 in2：1562052203
5.自定义对象锁(静态)
静态对象锁，多例有效
1 public class Test { 2 3 private static final String[] MY_LOCK = new String[]{}; 4 5 private void syncMethod1() { 6 synchronized (MY_LOCK) { 7 System.out.println("in1：" + System.currentTimeMillis() / 1000); 8 try { 9 Thread.sleep(5000); 10 } catch (InterruptedException e) { 11 e.printStackTrace(); 12 } 13 } 14 15 } 16 17 private void syncMethod2() { 18 synchronized (MY_LOCK) { 19 System.out.println("in2：" + System.currentTimeMillis() / 1000); 20 try { 21 Thread.sleep(5000); 22 } catch (InterruptedException e) { 23 e.printStackTrace(); 24 } 25 } 26 } 27 28 public static void main(String[] args) { 29 new Thread(new Runnable() { 30 public void run() { 31 new Test().syncMethod1(); 32 } 33 }).start(); 34 35 new Thread(new Runnable() { 36 public void run() { 37 new Test().syncMethod2(); 38 } 39 }).start(); 40 } 41 }
result in1：1562052289 in2：1562052294
