java.util.concurrent.locks.readwritelock接口允许一次读取多个线程，但一次只能写入一个线程。

• 读锁 - 如果没有线程锁定readwritelock进行写入，则多线程可以访问读锁。
• 写锁 - 如果没有线程正在读或写，那么一个线程可以访问写锁。

锁方法

以下是lock类中可用的重要方法的列表。

示例

以下testthread程序演示了readwritelock接口的这些方法。这里我们使用readlock()获取读锁定和writelock()来获取写锁定。

import java.util.concurrent.locks.reentrantreadwritelock;

public class testthread {

   private static final reentrantreadwritelock lock = new reentrantreadwritelock(true);

   private static string message = "a";

   public static void main(string[] args) throws interruptedexception{
      thread t1 = new thread(new writera());
      t1.setname("writer a");
      thread t2 = new thread(new writerb());
      t2.setname("writer b");
      thread t3 = new thread(new reader());
      t3.setname("reader");
      t1.start();
      t2.start();
      t3.start();
      t1.join();
      t2.join();
      t3.join();
   }

   static class reader implements runnable {

      public void run() {
         if(lock.iswritelocked()) {
            system.out.println("write lock present.");
         }   
         lock.readlock().lock();
         try {
            long duration = (long) (math.random() * 10000);
            system.out.println(thread.currentthread().getname() 
               + "  time taken " + (duration / 1000) + " seconds.");
            thread.sleep(duration);
         } catch (interruptedexception e) {
            e.printstacktrace();
         } finally {
            system.out.println(thread.currentthread().getname() +": "+ message );
            lock.readlock().unlock();
         }
      }
   }

   static class writera implements runnable {

      public void run() {
         lock.writelock().lock();
         try {
            long duration = (long) (math.random() * 10000);
            system.out.println(thread.currentthread().getname() 
               + "  time taken " + (duration / 1000) + " seconds.");
            thread.sleep(duration);
         } catch (interruptedexception e) {
            e.printstacktrace();
         } finally {
            message = message.concat("a");
            lock.writelock().unlock();
         }
      }
   }

   static class writerb implements runnable {

      public void run() {
         lock.writelock().lock();
         try {
            long duration = (long) (math.random() * 10000);
            system.out.println(thread.currentthread().getname() 
               + "  time taken " + (duration / 1000) + " seconds.");
            thread.sleep(duration);
         } catch (interruptedexception e) {
            e.printstacktrace();
         } finally {
            message = message.concat("b");
            lock.writelock().unlock();
         }
      }
   }
}

这将产生以下结果,如下所示 -

writer a  time taken 6 seconds.
write lock present.
writer b  time taken 2 seconds.
reader  time taken 0 seconds.
reader: aab