线程锁,解决并发请求

来源：互联网发布：工作任务分配软件编辑：程序博客网时间：2024/05/09 02:41

（1）

package com.example.multidownload;

import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.RandomAccessFile;

import android.os.Handler;

public class WriteThread extends Thread {
private String fileName;
private int startPosition;
private boolean state=true;
private int times;
private Handler handler;
public WriteThread(String fileName,int startPosition,Handler handler) {
super();
this.fileName=fileName;
this.startPosition=startPosition;
this.handler=handler;
}
@Override
public void run() {
super.run();
try {
RandomAccessFile randomAccessFile = new RandomAccessFile(fileName, "rwd");
randomAccessFile.seek(startPosition);
while (times<100) {
if(!state)
{
//java.lang.IllegalMonitorStateException: object not locked by thread before wait()
//即this.wait();周围也要加锁,不然会报上面的错
synchronized (this) {
System.out.println(WriteThread.this.getName()+"线程等待中........"+times);
handler.sendEmptyMessage(0);
this.wait();
}

}
System.out.println(WriteThread.this.getName()+"线程执行中........"+times);
randomAccessFile.writeChars("hello:"+WriteThread.this.getName()+"="+times+"\r\n");

times++;
Thread.sleep(100);
}
handler.sendEmptyMessage(1);
randomAccessFile.close();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
public void pauseWrite()
{
this.state=false;
}
public void resumeWrite()
{
this.state=true;
//java.lang.IllegalMonitorStateException: object not locked by thread before notifyAll()
//即this.notifyAll();外围也要加同步锁,不然会报上面的错
synchronized (this) {
this.notifyAll();
}
}

}

（2）

public class testThread {

/**
* @param 主/子线程同步,互斥打印(轮流打印10次,重复5变).............
*/
public static void main(String[] args) {
final Print print = new Print();

new Thread() {
public void run() {
for (int i = 0; i < 5; i++) {
print.printInSubThread(i);

}
};
}.start();
//主线程运行的代码放在子线程后,不然打印了了一变就成睡眠状态了，后面的代码就运行不了
for (int i = 0; i < 5; i++) {
print.printInMainThread(i);
}

}
/////////////////////打印/////////////////////////
public static class Print {
private boolean isPrintMainThread = true;

public synchronized void printInMainThread(int rowNums) {
while (!isPrintMainThread) {
// 子线程在打印,等待
try {
this.wait();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
for (int i = 0; i < 10; i++) {
System.out.println("printInMainThread" + i + "/" + rowNums);
}
isPrintMainThread = false;
this.notify();
}

public synchronized void printInSubThread(int rowNums) {
while (isPrintMainThread) {
// 主线程在打印,等待
try {
this.wait();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
for (int i = 0; i < 10; i++) {
System.out.println("printInSubThread:" + i + "/" + rowNums);
}
isPrintMainThread = true;
this.notify();
}
}

}

（3）

如何避免多个线程同时下载同一张图片(防止并发,要同步)?

final ReentrantLock reentrantLock = new ReentrantLock();
for (int i = 0; i < 10; i++) {
final int j=i;
new Thread(){
public void run() {
reentrantLock.lock();
System.out.println("hello:start:"+j);
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("hello:end:"+j);
reentrantLock.unlock();
};
}.start();
}

不同步(这样就并发了,各做各的事).....................

final ReentrantLock reentrantLock = new ReentrantLock();
for (int i = 0; i < 10; i++) {
final int j=i;
new Thread(){
public void run() {
//reentrantLock.lock();
System.out.println("hello:start:"+j);
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("hello:end:"+j);
//reentrantLock.unlock();
};
}.start();
}

（4）

如何避免多个线程同时调用一个方法,导致数据混乱(防止并发,要同步)?

public class testSyn {

/**
* @param args
*/
public static void main(String[] args) {
new Thread(){
public void run() {
while (true) {
go("WUXIFU");

}
};
}.start();
new Thread(){
public void run() {
while (true) {
go("wuyaoping");

}
};
}.start();

}

private static /*synchronized*/void go(String s) {
for (int i = 0; i < s.length(); i++) {
System.out.print(s.charAt(i));

try {
Thread.sleep(10);
} catch (InterruptedException e) {
e.printStackTrace();
}

}
System.out.println();
}

}

结果数据混乱(没有在方法里加synchronized)：

在方法里加synchronized

public class testSyn {

/**
* @param args
*/
public static void main(String[] args) {
new Thread(){
public void run() {
while (true) {
go("WUXIFU");

}
};
}.start();
new Thread(){
public void run() {
while (true) {
go("wuyaoping");

}
};
}.start();

}

private static synchronized void go(String s) {
for (int i = 0; i < s.length(); i++) {
System.out.print(s.charAt(i));

try {
Thread.sleep(10);
} catch (InterruptedException e) {
e.printStackTrace();
}

}
System.out.println();
}

}

结果正常:

(5)如何避免多线程请求同一个接口,只发送一次请求(只请求一次该接口)

package com.example.administrator.myapplication;import android.util.Log;import org.junit.Test;import java.lang.CloneNotSupportedException;import java.lang.Object;import java.lang.Override;import java.lang.System;import java.util.concurrent.locks.ReentrantLock;import static org.junit.Assert.*;/** * To work on unit tests, switch the Test Artifact in the Build Variants view. */public class ExampleUnitTest {    @Test    public void addition_isCorrect() throws Exception {        assertEquals(4, 2 + 2);        test();       test002();    }    private void test() {        final ReentrantLock reentrantLock = new ReentrantLock();        for (int i = 0; i < 10; i++) {            final int position = i;           new Thread(){               @Override               public void run() {                   super.run();                   final int position2=position;                 //  ReentrantLock   reentrantLock2 = new ReentrantLock();                   new Person(reentrantLock,position).sayHello(new Ihello() {                       public void goodBye() {                           System.out.println("成功了" + position2);                       }                   });               }           }.start();        }    }    private void test002() {        final ReentrantLock reentrantLock = new ReentrantLock();        final Person person = new Person(reentrantLock);        for (int i = 10; i < 20; i++) {            final int position = i;            new Thread(){                @Override                public void run() {                    super.run();                    final int position2=position;                   person.sayHello(new Ihello() {                       public void goodBye() {                           System.out.println("成功了" + position2);                       }                   },position2);                }            }.start();        }    }    public interface Ihello {        public void goodBye();    }    public class Person {        private  int position;        ReentrantLock reentrantLock;        public Person(ReentrantLock reentrantLock, int position) {            this.reentrantLock = reentrantLock;            this.position = position;        }        public Person(ReentrantLock reentrantLock) {            this.reentrantLock = reentrantLock;        }        public void sayHello(Ihello ihello) {                reentrantLock.lock();            System.out.println("start" + position);            ihello.goodBye();            System.out.println("end" + position);            try {                //TODO 所有在等待的同样任务将全部取消                reentrantLock.lockInterruptibly();            } catch (InterruptedException e) {                e.printStackTrace();            }            reentrantLock.unlock();            System.out.println("结尾" + position);        }        public void sayHello(Ihello ihello,int position) {            reentrantLock.lock();            System.out.println("start" + position);            ihello.goodBye();            System.out.println("end" + position);            try {                //TODO 所有在等待的同样任务将全部取消                reentrantLock.lockInterruptibly();            } catch (InterruptedException e) {                e.printStackTrace();            }            System.out.println("结尾" + position);            reentrantLock.unlock();        }    }}

返回结果：

java 并发

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