如何使用lock？lock 与synchronized 区别是什么？
2024-10-31 08:15:39
极客架构
Lock
就像同步块一样，
java.util.concurrent.locks.Lock是线程同步机制。但是，锁比同步块更灵活，更复杂。由于Lock是接口，因此需要使用其实现之一在应用程序中使用Lock。 ReentrantLock是Lock接口的一种此类实现。
Lock lock = new ReentrantLock();
lock.lock();
lock.unlock();Lock 与 synchronized 不同之处
1. Lock可以设置超时.而synchronized 则不可以设置。
Lock.tryLock(long timeout, TimeUnit timeUnit)2.synchronized 必须是在同一方法中。lock() 和unlock()可以在不同的方法中。
Lock的使用实例
在此示例中，程序将模拟打印的行为。您可以在不同的时间间隔内或同时向打印任务提交多个打印作业。打印机将从打印队列中取出一份作业并进行打印。其余工作将在那里等待。一旦打印机完成了手头的打印作业，它将从队列中选择另一个作业并开始打印。保持循环进行。
public class PrinterQueue {
private final Lock queueLock = new ReentrantLock();
public void printJob(Object document) {
queueLock.lock();
try {
long duration = new Random().nextInt(10000);
System.out.println(Thread.currentThread().getName() + ": PrintQueue: Printing a Job during "
+ (duration / 1000) + " seconds :: Time - " + new Date());
Thread.sleep(duration);
} catch (InterruptedException e) {
e.printStackTrace();
} finally {
queueLock.unlock();
System.out.printf("%s: The document has been printed\n", Thread.currentThread().getName());
}
}
}
class PrintingJob implements Runnable {
private PrinterQueue printerQueue;
public PrintingJob(PrinterQueue printerQueue) {
this.printerQueue = printerQueue;
}
@Override
public void run() {
System.out.printf("%s: Going to print a document\n", Thread.currentThread().getName());
printerQueue.printJob(new Object());
}
}测试
public class PrinterQueue {
private final Lock queueLock = new ReentrantLock();
public void printJob(Object document) {
queueLock.lock();
try {
long duration = new Random().nextInt(10000);
System.out.println(Thread.currentThread().getName() + ": PrintQueue: Printing a Job during "
+ (duration / 1000) + " seconds :: Time - " + new Date());
Thread.sleep(duration);
} catch (InterruptedException e) {
e.printStackTrace();
} finally {
queueLock.unlock();
System.out.printf("%s: The document has been printed\n", Thread.currentThread().getName());
}
}效果
"D:\Program Files\Java\jdk1.8.0_221\bin\java.exe" -Dvisualvm.id=15276093588700 "-javaagent:D:\Program Files\JetBrains\Toolbox\apps\IDEA-U\ch-0\201.6668.121\lib\idea_rt.jar=53022:D:\Program Files\JetBrains\Toolbox\apps\IDEA-U\ch-0\201.6668.121\bin" -Dfile.encoding=UTF-8 -classpath "D:\Program Files\Java\jdk1.8.0_221\jre\lib\charsets.jar;D:\Program Files\Java\jdk1.8.0_221\jre\lib\deploy.jar;D:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\access-bridge-64.jar;D:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\cldrdata.jar;D:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\dnsns.jar;D:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\jaccess.jar;D:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\jfxrt.jar;D:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\localedata.jar;D:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\nashorn.jar;D:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\sunec.jar;D:\Program Files\Java\jdk1.8.0_221\jre\lib\ext\sunjce_provider.jar;D:\Program 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com.demo.lock.LockExample
Thread 1: Going to print a document
Thread 9: Going to print a document
Thread 8: Going to print a document
Thread 5: Going to print a document
Thread 4: Going to print a document
Thread 6: Going to print a document
Thread 7: Going to print a document
Thread 3: Going to print a document
Thread 2: Going to print a document
Thread 0: Going to print a document
Thread 1: PrintQueue: Printing a Job during 2 seconds :: Time - Tue May 26 12:48:07 CST 2020
Thread 1: The document has been printed
Thread 9: PrintQueue: Printing a Job during 6 seconds :: Time - Tue May 26 12:48:09 CST 2020
Thread 9: The document has been printed
Thread 8: PrintQueue: Printing a Job during 2 seconds :: Time - Tue May 26 12:48:15 CST 2020
Thread 8: The document has been printed
Thread 5: PrintQueue: Printing a Job during 1 seconds :: Time - Tue May 26 12:48:18 CST 2020
Thread 5: The document has been printed
Thread 4: PrintQueue: Printing a Job during 9 seconds :: Time - Tue May 26 12:48:20 CST 2020
Thread 4: The document has been printed
Thread 6: PrintQueue: Printing a Job during 9 seconds :: Time - Tue May 26 12:48:29 CST 2020
Thread 6: The document has been printed
Thread 7: PrintQueue: Printing a Job during 7 seconds :: Time - Tue May 26 12:48:39 CST 2020
Thread 7: The document has been printed
Thread 3: PrintQueue: Printing a Job during 0 seconds :: Time - Tue May 26 12:48:47 CST 2020
Thread 3: The document has been printed
Thread 2: PrintQueue: Printing a Job during 2 seconds :: Time - Tue May 26 12:48:47 CST 2020
Thread 2: The document has been printed
Thread 0: PrintQueue: Printing a Job during 8 seconds :: Time - Tue May 26 12:48:50 CST 2020
Thread 0: The document has been printed
Process finished with exit code 0
该示例的主要的在PrinterQueue类的printJob（）方法中。当我们想使用锁来实现关键部分并确保只有一个执行线程运行代码块时，我们必须创建一个ReentrantLock对象。在方法的开始，我们必须使用lock（）方法来控制锁。
在关键部分的末尾，我们必须使用unlock（）方法释放锁的控制权，并允许其他线程运行该关键部分。如果您在关键部分的末尾不调用unlock（）方法，则正在等待该块的其他线程将永远处于等待状态，从而导致死锁情况。如果您在关键部分中使用try-catch块，请不要忘记将包含unlock（）方法的句子放在finally部分中
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