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概念:
1、在java环境下ReentrantLock和synchronized都是可重入锁
2、非重入锁会导致死锁
3、重入锁,传递给下一个方法,重复使用
重入锁测试代码:
package thread.pool;/*** 重入锁、非重入锁* @author Administrator**/
public class Test5 implements Runnable {public synchronized void get(){System.out.println(Thread.currentThread().getId() +"---get()");set();}public synchronized void set(){System.out.println(Thread.currentThread().getId() +"---set()");}@Overridepublic void run() {get();}public static void main(String[] args) {Test5 th = new Test5();new Thread(th).start();new Thread(th).start();new Thread(th).start();new Thread(th).start();new Thread(th).start();}
}
package thread.pool;import java.util.concurrent.locks.ReentrantLock;/*** 重入锁、非重入锁* @author Administrator**/
public class Test6 implements Runnable {ReentrantLock dd = new ReentrantLock();public void get(){dd.lock();System.out.println(Thread.currentThread().getId() +"---get()");set();dd.unlock();}public void set(){dd.lock();System.out.println(Thread.currentThread().getId() +"---set()");dd.unlock();}@Overridepublic void run() {get();}public static void main(String[] args) {Test6 th = new Test6();new Thread(th).start();new Thread(th).start();new Thread(th).start();new Thread(th).start();new Thread(th).start();}
}
读写锁的测试代码:
package thread.pool;import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantReadWriteLock;/*** * 读写锁* * @author Administrator**/
public class Test7 {static Map<String, Object> map = new HashMap<>();static ReentrantReadWriteLock da = new ReentrantReadWriteLock();static Lock r = da.readLock();static Lock w = da.writeLock();public static void get(String key) {r.lock();System.out.println(""+key+"正在进行----读----操作-----开始");try {Thread.sleep(100);Object object = map.get(key);System.out.println(""+key+"-"+object+"正在进行----读---操作-----结束");} catch (InterruptedException e) {e.printStackTrace();}finally {r.unlock();}}public static void set(String key, String value) {w.lock();System.out.println(""+key+"-"+value+"正在进行----写----操作-----开始");try {Thread.sleep(100);map.put(key, value);System.out.println(""+key+"-"+value+"正在进行----写----操作-----结束");} catch (InterruptedException e) {e.printStackTrace();}finally {w.unlock();}}public static void main(String[] args) {new Thread(new Runnable() {@Overridepublic void run() {for (int i = 0; i < 10; i++) {Test7.get(i+"");}}}).start();new Thread(new Runnable() {@Overridepublic void run() {for (int i = 0; i < 10; i++) {Test7.set(i+"", i+"");}}}).start();}
}
4、CAS无锁机制
举例:原子类底层实现保证线程安全,就是采用CAS无锁机制,CAS无锁机制效率比有效机制高
5、CAS体系中有三个参数,它包含三个参数CAS(V,E,N):v表示要更新的变量值,E表示预期值,N表示新值。仅当V值等于E值时,才会将V的值设为N,如果V值和E值不同,则说明已经有其他线程做了更新,则当前线程什么都不会做。最后,CAS返回当前V的真实值
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