Synchronization block (method) of Java multi-thread synchronization mechanism-synchronized and multi-thread synchronized

Synchronization block (method) of Java multi-thread synchronization mechanism-synchronized and multi-thread synchronized

During multi-threaded access, only one thread can use synchronized to modify the method or code block at the same time, solving the problem of resource sharing. The following code shows how to purchase five train tickets in three windows:

1 package com. jikexueyuan. thread; 2/* 3 * synchronized is not used, concurrency 4 */5 class RunnableDemo implements Runnable {6 private int tickets = 5; 7 @ Override 8 public void run () {9 for (int I = 0; I <10; I ++) {10 try {11 Thread. sleep (500); 12} catch (InterruptedException e) {13 e. printStackTrace (); 14} 15 if (tickets> 0) {16 System. out. println ("Ticket:" + tickets --); 17} 18} 19 20} 21} 22 23 public class ThreadTest {24 25 public static void main (String [] args) {26 RunnableDemo r = new RunnableDemo (); 27 Thread t1 = new Thread (r); 28 Thread t2 = new Thread (r); 29 Thread t3 = new Thread (r ); 30 t1.start (); 31 t2.start (); 32 t3.start (); 33} 34 35}

The result of one operation:

Ticket: 5 Ticket: 4 Ticket: 3 Ticket: 2 Ticket: 1 ticket: 2

After synchronized is used to synchronize a block:

1 package com. jikexueyuan. thread; 2/* 3 * use synchronized Blocks 4 */5 class RunnableDemo implements Runnable {6 private int tickets = 5; 7 @ Override 8 public void run () {9 for (int I = 0; I <10; I ++) {10 try {11 Thread. sleep (500); 12} catch (InterruptedException e) {13 e. printStackTrace (); 14} 15 synchronized (this) {16 if (tickets> 0) {17 System. out. println ("Ticket:" + tickets --); 18} 19} 20} 21} 22} 23 24 public class ThreadTest {25 26 public static void main (String [] args) {27 RunnableDemo r = new RunnableDemo (); 28 Thread t1 = new Thread (r); 29 Thread t2 = new Thread (r); 30 Thread t3 = new Thread (r ); 31 t1.start (); 32 t2.start (); 33 t3.start (); 34} 35 36}

Use the synchronized synchronization method:

1 package com. jikexueyuan. thread; 2/* 3 * use synchronized synchronization method 4 */5 class RunnableDemo implements Runnable {6 private int tickets = 5; 7 @ Override 8 public void run () {9 for (int I = 0; I <10; I ++) {10 show (); 11} 12} 13 public synchronized void show () {14 if (tickets> 0) {15 System. out. println ("Ticket:" + tickets --); 16} 17} 18} 19 20 public class ThreadTest {21 22 public static void main (String [] args) {23 RunnableDemo r = new RunnableDemo (); 24 Thread t1 = new Thread (r); 25 Thread t2 = new Thread (r); 26 Thread t3 = new Thread (r ); 27 t1.start (); 28 t2.start (); 29 t3.start (); 30} 31 32}

Whether synchronized synchronization block or synchronization method is used, the running results are reasonable:

Ticket: 5 Ticket: 4 Ticket: 3 Ticket: 2 Ticket: 1

Thinking: volatile is another synchronization mechanism. Can it? Reference my linked article: Java Theory and Practice: Correct Use of Volatile variable http://www.ibm.com/developerworks/cn/java/j-jtp06197.html