package com.company;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
/**
* 学习《Java核心技术 卷一》并发章节，同步内容。
* 关于ReentrantLock的使用。
*/
public class ConcurrencyDemo {
private Lock lock = new ReentrantLock();
/**
* 不带锁的线程，在r的语句块中，每一步都可能会被打断。
*/
public void unsynchConcurrencyTest() {
for (int i = 0; i < 100; i++) {
Runnable r = () ->
{
try {
while (true) {
int num = (int) (100 * Math.random());
System.out.println(num + "_19");
Thread.sleep(1000);
System.out.println(num + "_21");
}
} catch (InterruptedException e) {
}
};
Thread t = new Thread(r);
t.start();
}
}
/**
* 这是一个带锁的线程demo。
* 可以看出：
* 第一个循环开始的时候（也就是第一格线程被创建，一共有10个Thread被创建），
* 第一格Thread为：Thread[Thread-6,5,main]
* 在lock()之后，sleep()期间，执行下一个线程。
* （猜测是t.start()之后先不管了，就是执行run，然后在开始下一个Thread，也就是这一套程序只会执行t.start()，把线程都启动/创建，
* 接下来的就是线程自己run）
* 在sleep（）的时候，其他线程准备闯入执行，
* 首先是其他线程请求获取锁，然后发现没有unlock，于是被阻塞。借着其他的Thread请求，但是都在lock的地方被阻塞。
* 接下来就T这个拥有锁的Thread（Thread[Thread-6,5,main]）开始执行，知道unlock。
* 但是这个程序并没有unlock，所以一直都会处于Thread[Thread-6,5,main]这个线程中。
*
* 输出的片段：
* Thread[Thread-6,5,main]:Try to get lock...
* Thread[Thread-8,5,main]:Try to get lock...
* 31
* Thread[Thread-1,5,main]:Try to get lock...
* Thread[Thread-2,5,main]:Try to get lock...
* Thread[Thread-0,5,main]:Try to get lock...
* Thread[Thread-7,5,main]:Try to get lock...
* Thread[Thread-5,5,main]:Try to get lock...
* Thread[Thread-9,5,main]:Try to get lock...
* Thread[Thread-4,5,main]:Try to get lock...
* Thread[Thread-3,5,main]:Try to get lock...
* 31
* Thread[Thread-6,5,main]:loop done...
* 27
* 27
* Thread[Thread-6,5,main]:loop done...
* 23
* 23
* Thread[Thread-6,5,main]:loop done...
* 5
* 5
* Thread[Thread-6,5,main]:loop done...
* 25
*/
public void lockOneConcurrencyTest() {
for (int i = 0; i < 10; i++) {
Runnable r = () ->
{
try {
var cur = Thread.currentThread();
System.out.println(cur + ":Try to get lock...");
lock.lock();
while (true) {
int num = (int) (100 * Math.random());
System.out.println(num);
Thread.sleep(1000);
System.out.println(num);
System.out.println(cur + ":loop done...");
}
} catch (InterruptedException e) {
}
finally {
lock.unlock();
System.out.println("Free lock...");
}
};
Thread t = new Thread(r);
t.start();
}
}
/**
* 确保每一次while都能够被完整的执行而不被打断。
*
* 每一个程序在请求锁的时候，如果它持有，那么就会先调用持有的那段代码，执行完之后，才会执行本段申请锁的之后的代码。
* 也就是持有计数(hold count)机制，可重入机制（reentrant）。
*
* 可以从输出看出，在Got lock之前会有线程执行Try to get lock...
* 也就是只有lock()到unlock()区间的代码被保护。
* 在其他线程即将执行这一段代码(lock()和unlock()之间的代码)的时候，
* 就会被阻塞，直到前一个调用lock的那一段执行完之后这一段才会被执行。
*
* 输出：
*
* C:\ForProgram\jdk-10.0.2\bin\java.exe "-javaagent:C:\ForProgram\JetBrains\IntelliJ IDEA Community Edition 2018.1.1\lib\idea_rt.jar=7209:C:\ForProgram\JetBrains\IntelliJ IDEA Community Edition 2018.1.1\bin" -Dfile.encoding=UTF-8 -classpath C:\Users\WuJing\Desktop\Learn\Java\ReviewJava\Blobs\out\production\Blobs com.company.ConcurrencyDemo
* Thread[Thread-2,5,main]:Try to get lock...
* Thread[Thread-9,5,main]:Try to get lock...
* Thread[Thread-8,5,main]:Try to get lock...
* Thread[Thread-6,5,main]:Try to get lock...
* Thread[Thread-8,5,main]:Got lock...
* Thread[Thread-4,5,main]:Try to get lock...
* Thread[Thread-3,5,main]:Try to get lock...
* Thread[Thread-1,5,main]:Try to get lock...
* Thread[Thread-5,5,main]:Try to get lock...
* 7
* Thread[Thread-0,5,main]:Try to get lock...
* Thread[Thread-7,5,main]:Try to get lock...
* 7
* Thread[Thread-8,5,main]:loop done...
* Thread[Thread-6,5,main]:Got lock...
* Free lock...
* 45
* Thread[Thread-8,5,main]:Try to get lock...
* 45
* Thread[Thread-6,5,main]:loop done...
* Free lock...
* Thread[Thread-6,5,main]:Try to get lock...
* Thread[Thread-9,5,main]:Got lock...
* 58
* 58
* Thread[Thread-9,5,main]:loop done...
* Free lock...
* Thread[Thread-9,5,main]:Try to get lock...
* Thread[Thread-4,5,main]:Got lock...
* 13
* 13
* Thread[Thread-4,5,main]:loop done...
* Free lock...
* Thread[Thread-4,5,main]:Try to get lock...
* Thread[Thread-4,5,main]:Got lock...
* 99
* 99
* Thread[Thread-4,5,main]:loop done...
* Free lock...
* Thread[Thread-4,5,main]:Try to get lock...
* Thread[Thread-3,5,main]:Got lock...
* 11
* 11
* Thread[Thread-3,5,main]:loop done...
* Free lock...
* Thread[Thread-3,5,main]:Try to get lock...
* Thread[Thread-2,5,main]:Got lock...
* 72
* 72
* Thread[Thread-2,5,main]:loop done...
* Free lock...
* Thread[Thread-1,5,main]:Got lock...
* Thread[Thread-2,5,main]:Try to get lock...
* 12
* 12
* Thread[Thread-1,5,main]:loop done...
* Free lock...
* Thread[Thread-1,5,main]:Try to get lock...
* Thread[Thread-5,5,main]:Got lock...
* 68
* 68
* Thread[Thread-5,5,main]:loop done...
* Thread[Thread-0,5,main]:Got lock...
* 38
* Free lock...
* Thread[Thread-5,5,main]:Try to get lock...
* 38
* Thread[Thread-0,5,main]:loop done...
* Free lock...
* Thread[Thread-0,5,main]:Try to get lock...
* Thread[Thread-0,5,main]:Got lock...
* 2
* 2
* Thread[Thread-0,5,main]:loop done...
* Free lock...
* Thread[Thread-0,5,main]:Try to get lock...
* Thread[Thread-7,5,main]:Got lock...
* 8
* 8
* Thread[Thread-7,5,main]:loop done...
* Free lock...
* Thread[Thread-8,5,main]:Got lock...
* Thread[Thread-7,5,main]:Try to get lock...
* 24
* 24
* Thread[Thread-8,5,main]:loop done...
* Free lock...
* Thread[Thread-6,5,main]:Got lock...
* 9
* Thread[Thread-8,5,main]:Try to get lock...
*
* Process finished with exit code -1
*
*/
public void lockConcurrencyTest() {
for (int i = 0; i < 10; i++) {
Runnable r = () ->
{
while (true) {
try {
var cur = Thread.currentThread();
System.out.println(cur + ":Try to get lock...");
lock.lock();
System.out.println(cur + ":Got lock...");
int num = (int) (100 * Math.random());
System.out.println(num);
Thread.sleep(1000);
System.out.println(num);
System.out.println(cur + ":loop done...");
} catch (InterruptedException e) {
}
finally {
lock.unlock();
System.out.println("Free lock...");
}
}
};
Thread t = new Thread(r);
t.start();
}
}
public static void main(String[] args) {
ConcurrencyDemo c = new ConcurrencyDemo();
c.lockConcurrencyTest();
}
}
Java核心技术卷一并发章节同步中锁ReentrantLock的探究
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转载自blog.csdn.net/qq_39422041/article/details/81435387
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