锁(重入锁，读写锁)
它们具有比synchronized更为强大的功能，并且有嗅探锁定、多路分支等功能。
重入锁，在需要进行同步的代码部分加上锁定，但不要忘记最后一定要释放锁定，不然会造成锁永远无法释放，其他线程永远进不去的结果。
package edu.sdut.lock;
import java.util.concurrent.CopyOnWriteArrayList;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
public class UseReentrantLock {
private Lock lock = new ReentrantLock();
public void method1(){
try {
lock.lock();
System.out.println("当前线程:" + Thread.currentThread().getName() + "进入method1..");
Thread.sleep(1000);
System.out.println("当前线程:" + Thread.currentThread().getName() + "退出method1..");
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
} finally {
lock.unlock();
}
}
public void method2(){
try {
lock.lock();
System.out.println("当前线程:" + Thread.currentThread().getName() + "进入method2..");
Thread.sleep(2000);
System.out.println("当前线程:" + Thread.currentThread().getName() + "退出method2..");
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
} finally {
lock.unlock();
}
}
public static void main(String[] args) {
final UseReentrantLock ur = new UseReentrantLock();
Thread t1 = new Thread(new Runnable() {
@Override
public void run() {
ur.method1();
ur.method2();
}
}, "t1");
t1.start();
try {
Thread.sleep(10);
} catch (InterruptedException e) {
e.printStackTrace();
}
//System.out.println(ur.lock.getQueueLength());
}
}
锁的等待/通知
在使用Lock的时候，可以使用一个新的等待/通知类，Condition,这个Condition一定是针对具体，某一把锁的。也就是在只有锁的基础上才会产生Condition.
多个Condition的使用：
package edu.sdut.lock; import java.util.concurrent.locks.Condition; import java.util.concurrent.locks.Lock; import java.util.concurrent.locks.ReentrantLock; public class UseManyCondition { private ReentrantLock lock = new ReentrantLock(); private Condition c1 = lock.newCondition(); private Condition c2 = lock.newCondition(); public void m1(){ try { lock.lock(); System.out.println("当前线程：" +Thread.currentThread().getName() + "进入方法m1等待.."); //等待 c1.await(); System.out.println("当前线程：" +Thread.currentThread().getName() + "方法m1继续.."); } catch (Exception e) { e.printStackTrace(); } finally { lock.unlock(); } } public void m2(){ try { lock.lock(); System.out.println("当前线程：" +Thread.currentThread().getName() + "进入方法m2等待.."); c1.await(); System.out.println("当前线程：" +Thread.currentThread().getName() + "方法m2继续.."); } catch (Exception e) { e.printStackTrace(); } finally { lock.unlock(); } } public void m3(){ try { lock.lock(); System.out.println("当前线程：" +Thread.currentThread().getName() + "进入方法m3等待.."); c2.await(); System.out.println("当前线程：" +Thread.currentThread().getName() + "方法m3继续.."); } catch (Exception e) { e.printStackTrace(); } finally { lock.unlock(); } } public void m4(){ try { lock.lock(); System.out.println("当前线程：" +Thread.currentThread().getName() + "唤醒.."); //唤醒 相当于synchronized中的 wait/notify //lock.signal(); c1.signalAll(); } catch (Exception e) { e.printStackTrace(); } finally { lock.unlock(); } } public void m5(){ try { lock.lock(); System.out.println("当前线程：" +Thread.currentThread().getName() + "唤醒.."); c2.signal(); } catch (Exception e) { e.printStackTrace(); } finally { lock.unlock(); } } public static void main(String[] args) { final UseManyCondition umc = new UseManyCondition(); Thread t1 = new Thread(new Runnable() { @Override public void run() { umc.m1(); } },"t1"); Thread t2 = new Thread(new Runnable() { @Override public void run() { umc.m2(); } },"t2"); Thread t3 = new Thread(new Runnable() { @Override public void run() { umc.m3(); } },"t3"); Thread t4 = new Thread(new Runnable() { @Override public void run() { umc.m4(); } },"t4"); Thread t5 = new Thread(new Runnable() { @Override public void run() { umc.m5(); } },"t5"); t1.start();// c1 t2.start();// c1 t3.start();// c2 try { Thread.sleep(2000); } catch (InterruptedException e) { e.printStackTrace(); } t4.start();// c1 try { Thread.sleep(2000); } catch (InterruptedException e) { e.printStackTrace(); } t5.start();// c2 } }
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Lock/Condition其他方法和使用
Lock lock = new ReentrantLock(boolean isFair);
lock用法：
tryLock();尝试获得锁
ReentrantReadWriteLock（读写锁）
读写锁ReentrantReadWriteLock，其核心就是实现读写分离的锁，在高并发访问下，尤其是读多写少的情况下，性能要远高于重写锁。
对于Synchronized、ReentrantLock，同一时间内只能有一个线程访问被锁定的代码，那么读写锁则不同，其本质是分离两个锁，即读锁和写锁。在读锁下，多个线程呢个可以并发的进行访问，但是在写锁的时候，只能顺序的访问。
读读共享、写写互斥、读写互斥。
import java.util.concurrent.locks.ReentrantReadWriteLock; import java.util.concurrent.locks.ReentrantReadWriteLock.ReadLock; import java.util.concurrent.locks.ReentrantReadWriteLock.WriteLock; public class UseReentrantReadWriteLock { private ReentrantReadWriteLock rwLock = new ReentrantReadWriteLock(); private ReadLock readLock = rwLock.readLock(); private WriteLock writeLock = rwLock.writeLock(); public void read(){ try { readLock.lock(); System.out.println("当前线程:" + Thread.currentThread().getName() + "进入..."); Thread.sleep(3000); System.out.println("当前线程:" + Thread.currentThread().getName() + "退出..."); } catch (Exception e) { e.printStackTrace(); } finally { readLock.unlock(); } } public void write(){ try { writeLock.lock(); System.out.println("当前线程:" + Thread.currentThread().getName() + "进入..."); Thread.sleep(3000); System.out.println("当前线程:" + Thread.currentThread().getName() + "退出..."); } catch (Exception e) { e.printStackTrace(); } finally { writeLock.unlock(); } } public static void main(String[] args) { final UseReentrantReadWriteLock urrw = new UseReentrantReadWriteLock(); Thread t1 = new Thread(new Runnable() { @Override public void run() { urrw.read(); } }, "t1"); Thread t2 = new Thread(new Runnable() { @Override public void run() { urrw.read(); } }, "t2"); Thread t3 = new Thread(new Runnable() { @Override public void run() { urrw.write(); } }, "t3"); Thread t4 = new Thread(new Runnable() { @Override public void run() { urrw.write(); } }, "t4"); //t1.start(); //t2.start(); //t1.start(); // R //t3.start(); // W t3.start(); t4.start(); } } |