A read-write lock
1.1 ReentrantReadWriteLock
The reentrantReadWriteloc solution mainly solves read-read sharing, read-write mutual exclusion. In the scenario of more reads and less writes, read-write locks have higher performance.
1.2 Case Code
1. Resource class
package com.ljf.thread.readwritelock;
import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.locks.ReadWriteLock;
import java.util.concurrent.locks.ReentrantLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;
/**
* @ClassName: MyResources
* @Description: TODO
* @Author: admin
* @Date: 2023/05/21 11:33:08
* @Version: V1.0
**/
public class MyResources {
ReentrantLock mylock = new ReentrantLock();
Map<String,String> resultMap=new HashMap<>();
ReadWriteLock myrwLock=new ReentrantReadWriteLock();
public void writeSomething(String key,String value){
myrwLock.writeLock().lock();
try {
System.out.println("Thread: " + Thread.currentThread().getName() + "Writing...");
Thread. sleep(500);
resultMap. put(key, value);
System.out.println("Thread: " + Thread.currentThread().getName() + "Write completed...");
} catch (InterruptedException e) {
e.printStackTrace();
}
finally {
myrwLock.writeLock().unlock();
}
}
public void readSomething(String key){
myrwLock. readLock(). lock();
try {
System.out.println("Thread: " + Thread.currentThread().getName() + "Reading...");
resultMap. get(key);
Thread. sleep(200);
System.out.println("Thread: " + Thread.currentThread().getName() + "Read completed...");
} catch (InterruptedException e) {
e.printStackTrace();
}
finally {
myrwLock.readLock().unlock();
}
}
}
2. Call class
package com.ljf.thread.readwritelock;
/**
* Hello world!
*
*/
public class App
{
public static void main( String[] args )
{
System.out.println( "Hello World!" );
MyResources myResources = new MyResources();
for(int k=0;k<10;k++){
final int m=k;
new Thread(new Runnable() {
@Override
public void run() {
myResources.writeSomething("do" + m,m + "");
}
}).start();
}
System.out.println("=====");
for(int k=0;k<10;k++){
final int m=k;
new Thread(new Runnable() {
@Override
public void run() {
myResources. readSomething("do" + m);
}
}).start();
}
}
}
3. Execution results: The writing threads are mutually exclusive, one thread finishes writing, and the other writes; the reading thread is shared, and multiple threads can read at the same time
Hello World!
Thread: Thread-1 is writing…
=====
Thread: Thread-1 write complete…
Thread: Thread-3 is writing…
Thread: Thread-3 write complete…
Thread: Thread-0 is writing…
Thread: Thread-0 write complete…
Thread: Thread-2 is writing…
Thread: Thread-2 write complete…
Thread: Thread-4 is writing…
Thread: Thread-4 write complete…
Thread: Thread-5 is writing…
Thread: Thread-5 write complete…
Thread: Thread-6 is writing…
Thread: Thread-6 write complete…
Thread: Thread-7 is writing…
Thread: Thread-7 write complete…
Thread: Thread-8 is writing…
Thread: Thread-8 write complete…
Thread: Thread-9 is writing…
Thread: Thread-9 write complete…
Thread: Thread-10 is reading…
Thread: Thread-11 is reading…
Thread: Thread-12 is reading…
Thread: Thread-13 is reading…
Thread: Thread-14 is reading…
Thread: Thread-15 is reading…
Thread: Thread-17 is reading…
Thread: Thread-18 is reading…
Thread: Thread-16 is reading…
Thread: Thread-19 is reading…
Thread: Thread-15 Read complete…
Thread: Thread-19 Read complete…
Thread: Thread-16 Read complete…
Thread: Thread-12 Read complete…
Thread: Thread-14 Read complete…
Thread: Thread-11 Read complete…
Thread: Thread-13 Read complete…
Thread: Thread-10 read complete…
Thread: Thread-18 Read complete…
Thread: Thread-17 Read complete…
1.3 Case Code
Call class
package com.ljf.thread.readwritelock;
/**
* Hello world!
*
*/
public class App
{
public static void main( String[] args )
{
System.out.println( "Hello World!" );
MyResources myResources = new MyResources();
for(int k=0;k<10;k++){
final int m=k;
new Thread(new Runnable() {
@Override
public void run() {
myResources.writeSomething("do" + m,m + "");
}
}).start();
}
System.out.println("=====");
for(int k=0;k<10;k++){
final int m=k;
new Thread(new Runnable() {
@Override
public void run() {
myResources. readSomething("do" + m);
}
}).start();
}
for (int i = 1; i <=3; i ++ ) {
final int m=i;
new Thread(new Runnable() {
@Override
public void run() {
myResources.writeSomething("do" + m,m + "");
}
}).start();
}
}
}
Result: Read-write mutual exclusion, read-read sharing, when the read thread is not completed, other write threads cannot acquire the lock.
Thread: Thread-0 is writing…
=====
Thread: Thread-0 write complete…
Thread: Thread-1 is writing…
Thread: Thread-1 write complete…
Thread: Thread-2 is writing…
Thread: Thread-2 write complete…
Thread: Thread-3 is writing…
Thread: Thread-3 write complete…
Thread: Thread-4 is writing…
Thread: Thread-4 write complete…
Thread: Thread-5 is writing…
Thread: Thread-5 write complete…
Thread: Thread-6 is writing…
Thread: Thread-6 write complete…
Thread: Thread-7 is writing…
Thread: Thread-7 write complete…
Thread: Thread-8 is writing…
Thread: Thread-8 write complete…
Thread: Thread-9 is writing…
Thread: Thread-9 write complete…
Thread: Thread-10 is reading…
Thread: Thread-11 is reading…
Thread: Thread-12 is reading…
Thread: Thread-13 is reading…
Thread: Thread-14 is reading…
Thread: Thread-16 is reading…
Thread: Thread-15 is reading…
Thread: Thread-17 is reading…
Thread: Thread-19 is reading…
Thread: Thread-18 is reading…
Thread: Thread-11 Read complete…
Thread: Thread-10 read complete…
Thread: Thread-12 Read complete…
Thread: Thread-16 Read complete…
Thread: Thread-14 Read complete…
Thread: Thread-18 Read complete…
Thread: Thread-19 Read complete…
Thread: Thread-13 Read complete…
Thread: Thread-17 Read complete…
Thread: Thread-15 Read complete…
Thread: Thread-20 is writing…
Thread: Thread-20 write complete…
Thread: Thread-21 is writing…
Thread: Thread-21 Write complete…
Thread: Thread-22 is writing…
Thread: Thread-22 write completed…