4. Multi-thread synchronization

First, synchronization: synchronized

Sync Concurrency Multiple threads access the same resource to ensure resource security ----> Thread safety

• Sync Block:

Synchronized (Reference type | this | class. Class) {

}

• Synchronization method: public static synchronized void ...---->web12306

web12306 Code implementation:

Package com.cust.syn;/** * Description: Synchronizing concurrent multiple threads accessing the same resource * synchronized thread safety * @author Cookie */public class SynDemo01 {public S tatic void Main (string[] args) {//Real role Web12306 w = new Web12306 ();//three agent roles thread T1 = new Thread (W, "passer-by"); Thread t2 = new Thread (W, "Ox B"); thread t3 = new Thread (W, "Siege Lion"); T1.start (); T2.start (); T3.start ();}}    Class Web12306 implements Runnable {Private Boolean flag = true; int num = ten; @Overridepublic void Run () {while (flag) {TEST5 ();}} The lock resource is incorrect---> thread unsafe rate Comparison high public void Test5 () {//a B csynchronized ((Integer) num) {//Lock if (num <= 0) {flag = Fals e;//thread end return;} A b ctry {thread.sleep ($);//runnable cannot throw an exception outside} catch (Interruptedexception e) {e.printstacktrace ();} System.out.println (Thread.CurrentThread (). GetName () + "grabbed the first" + num--+ "Ticket");}} A b = 0 c = -1//lock range is incorrect---> thread unsafe rate Comparison high public void test4 () {//a B csynchronized (this) {//Lock the object that calls this method is Web12306if ( Num <=0) {flag = false;//thread end return;}} A b ctry {thread.sleep ($);//runnable cannot throw an exception outside} catch(Interruptedexception e) {E.printstacktrace ();} System.out.println (Thread.CurrentThread (). GetName () + "grabbed the first" + num--+ "ticket"); A b = 0 c = -1//lock sync block---> Line shuo full speed low public void test3 () {synchronized (this) {///Lock the object that called this method is web12306if (num <=0 {flag = false;//thread end return;} try {thread.sleep;//runnable cannot throw an exception outside} catch (Interruptedexception e) {e.printstacktrace ();} System.out.println (Thread.CurrentThread (). GetName () + "grabbed the first" + num--+ "Ticket");}} Locking Method---> Line shuo Full speed low public synchronized void Test2 () {if (num <=0) {flag = false;//thread end return;} try {thread.sleep;//runnable cannot throw an exception outside} catch (Interruptedexception e) {e.printstacktrace ();} System.out.println (Thread.CurrentThread (). GetName () + "grabbed the first" + num--+ "ticket"); Concurrency does not handle----> thread restless full rate lower public void test1 () {if (num <=0) {flag = false;//thread end return;} try {thread.sleep;//runnable cannot throw an exception outside} catch (Interruptedexception e) {e.printstacktrace ();} System.out.println (Thread.CurrentThread (). GetName () + "grabbed the first" + num--+ "Ticket");}}

Second, the single case mode　

Lazy and a hungry man-style

Package com.cust.syn;/** * Singleton mode * GC JVM trash Runtime * Lazy type: Double checking double check * 1. Constructor privatization * 2. Declaring a private static variable *  3. Create a common static method, access the variable, and make sure that there is a variable * a hungry man: * * @author Cookie */public class Singletondemo {}/** * lazy: Double checking double-check * 1. Constructor privatization * 2. Declare a private static variable * 3. Create a common static method, access the variable, and make sure that there is a variable * @author cookie */class jvm{private static JVM jvm;private JVM () {}public static JVM getinstance () {if (null = = JVM) {//Increase efficiency, do not enter the method if the object already exists synchronized (Jvm.class) {// Static method cannot call Thisif (NULL==JVM) {//If not present, create object security JVM = new JVM ();}}} return JVM;}} /** * A hungry man: * 1. Constructor privatization * 2. Declare a private static variable and instantiate the variable at the same time * 3. Create a common static method, Access variable * @author cookie */class jvm2{private static JV M2 JVM = new JVM2 ();p rivate JVM2 () {}public static JVM2 getinstance () {///Do not use this method, the variable may be initialized to the return JVM;}} /** * class loaded during use, Delay load time (MYJVM) a hungry man recommended * @author cookie */class jvm3{private static class Myjvm{private static JVM3 JVM = new JVM3 ();} Private JVM3 () {}public static JVM3 getinstance () {//does not use this method and does not load Myjvmreturn MYJVM.JVM;}}

Three, deadlock: Too much synchronization is prone to deadlock

/** * Description: Deadlock: Too much synchronization easy to cause deadlock * @author Cookie */public class SynDemo03 {public static void main (string[] args) {Object g = n EW object (); object m = new Object (); Test T1 = new test (G,M); Test2 t2 = new Test2 (g,m); Thread proxy = new thread (t1); Thread Proxy2 = new Thread (t2);p Roxy.start ();p Roxy2.start ();}} Class Test implements Runnable{object Goods;object money;public Test (object goods, object money) {this.goods = Goods;this. Money = money;} @Overridepublic void Run () {test ();} public void Test () {synchronized (goods) {try {Thread.Sleep ($)} catch (Interruptedexception e) {e.printstacktrace ();} Synchronized (Money) {}}system.out.println ("Pay by Hand");}} Class Test2 implements Runnable{object Goods;object money;public Test2 (object goods, object money) {this.goods = Goods;thi S.money = money;} @Overridepublic void Run () {test ();} public void Test () {synchronized (money) {try {Thread.Sleep ($)} catch (Interruptedexception e) {e.printstacktrace ();} Synchronized (goods) {}}system.out.println ("hand Delivery");}}

Iv. Resolve deadlocks: Producer Consumer semaphore method

Package com.cust.pro;/** * A scene common resource producer consumer mode Semaphore Method object:wait () Release lock wait Sleep () do not release lock * Notify ()/notifyall () wake-up wait * * @au Thor Cookie */class Movie {private String pic;//semaphore//semaphore//Flag---->t producer production, consumer wait, production finished after production, wake-up consumer//flag----&GT;F Consumer  Fee, producer waits, consumer consumer finishes, wake producer private Boolean flag = True;public synchronized void Play (String pic) {if (!flag) {//consumer consumer producer waits for try {this.wait ();} catch (Interruptedexception e) {e.printstacktrace ();}} try {thread.sleep;} catch (Interruptedexception E1) {e1.printstacktrace ();} Production end this.pic = pic; System.out.println ("produced:" + pic);//wake-up consumer, this.notifyall ();//producer End this.flag = false;} public synchronized Void Watch () {if (flag) {//producer production, consumer waits for try {this.wait ();} catch (Interruptedexception e) {E.printstack Trace ();}} Consumer consumption try {thread.sleep ($);} catch (Interruptedexception e) {e.printstacktrace ();} Consumption completed System.out.println ("consumption:" + this.pic);//wake-up producer This.notify ();//consumer waits for this.flag = true;}} Class Player implements Runnable{private Movie m;public Player (Movie m) {this.m = m;} @Overridepublic void Run () {for (int i = 0; i <; i++) {if (0==i%2) {M.play ("left Tsing Lung");} Else{m.play ("Right white Tiger");}}} Class Watcher implements Runnable{private movie M;public watcher (Movie m) {this.m = m;} @Overridepublic void Run () {for (int i = 0; i <; i++) {M.watch ();}}} public class App {public static void main (string[] args) {//common resource movie m = new Movie ();//multithreaded Player P = new player (m); Watcher W = new Watcher (m); new Thread (P). Start (); new Thread (W). Start ();}}

　　

4. Multi-thread synchronization