Java同步和锁机制代码实现
Java实现同步有两种方法，一是利用关键字synchronize来同步类、对象、方法，二是用Lock实现同步。Lock实现提供了比使用synchronize方法和语句可获得的更广泛的锁定操作，它能以更优雅的方式处理线程同步问题，但是用synchronize修饰的方法或者语句块在代码执行完之后锁自动释放，而用Lock需要我们手动释放锁，所以为了保证锁最终被释放（发生异常情况），要把互斥区放在try内，释放锁放在finally内。
以下为实现方法：
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import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; import java.util.concurrent.Future; import java.util.concurrent.locks.Lock; import java.util.concurrent.locks.ReadWriteLock; import java.util.concurrent.locks.ReentrantLock; import java.util.concurrent.locks.ReentrantReadWriteLock; //Lock机制 public class TestLock { public Lock lock = new ReentrantLock(); public double lockValue = 0d; public int addTime = 0; public void addLockValue(double v) { lock.lock(); System.out.println("add Time: " + addTime); try { Thread.sleep(1500); } catch (Exception e) { e.printStackTrace(); } lockValue += v; addTime++; System.out.println("Value: " + getLockValue()); lock.unlock(); } public double getLockValue() { return this.lockValue; } public static void main(String[] args) { try{ final TestLock tl = new TestLock(); Runnable task1 = new Runnable() { public void run() { tl.addLockValue(55.55); } }; Runnable task2 = new Runnable() { public void run() { System.out.println("Last Value: " + tl.getLockValue()); } }; ExecutorService service = Executors.newCachedThreadPool(); Future future = null; for(int i=0; i<3; i++) { future = service.submit(task1); } future.get(); service.submit(task2); future.get(); service.shutdownNow(); } catch(Exception e) { e.printStackTrace(); } } } //读写锁机制 public class TestLock { public ReadWriteLock lock = new ReentrantReadWriteLock(); public double lockValue = 0d; public int addTime = 0; public void addLockValue(double v) { Lock wlock =lock.writeLock(); wlock.lock(); System.out.println("add Time: " + addTime); try { Thread.sleep(1000); } catch (Exception e) { e.printStackTrace(); } lockValue += v; addTime++; System.out.println("Value: " + getLockValue()); wlock.unlock(); } public double getLockValue() { Lock rlock = lock.readLock(); rlock.lock(); try { Thread.sleep(1000); } catch (Exception e) { } try { return this.lockValue; } finally { rlock.unlock(); } } public static void main(String[] args) { try{ final TestLock tl = new TestLock(); Runnable task1 = new Runnable() { public void run() { tl.addLockValue(55.55); } }; Runnable task2 = new Runnable() { public void run() { System.out.println("Last Value: " + tl.getLockValue()); } }; ExecutorService service = Executors.newCachedThreadPool(); Future future = null; for(int i=0; i<3; i++) { future = service.submit(task1); } future.get(); for(int i=0; i<2; i++) { service.submit(task2); } future.get(); service.shutdownNow(); } catch(Exception e) { e.printStackTrace(); } } } //同步机制，可以同步类或方法 public class TestLock { public double lockValue = 0d; public int addTime = 0; public synchronized void addLockValue(double v) { System.out.println("add Time: " + addTime); try { Thread.sleep(1000); } catch (Exception e) { } finally { lockValue += v; addTime++; System.out.println("Value: " + getLockValue()); } } public double getLockValue() { try { Thread.sleep(1000); } catch (Exception e) { } return this.lockValue; } public static void main(String[] args) { try{ final TestLock tl = new TestLock(); Runnable task1 = new Runnable() { public void run() { tl.addLockValue(55.55); } }; Runnable task2 = new Runnable() { public void run() { System.out.println("Last Value: " + tl.getLockValue()); } }; ExecutorService service = Executors.newCachedThreadPool(); Future future = null; for(int i=0; i<3; i++) { future = service.submit(task1); } future.get(); for(int i=0; i<2; i++) { service.submit(task2); } future.get(); service.shutdownNow(); } catch(Exception e) { e.printStackTrace(); } } } //wait、notify、notifyAll public class TestLock { public double lockValue = 0d; public int addTime = 0; public Object object = new Object(); public synchronized void addLockValue(double v) { System.out.println("add Time: " + addTime); lockValue += v; addTime++; System.out.println("Value: " + getLockValue()); } public double getLockValue() { return this.lockValue; } public static void main(String[] args) { try{ final TestLock tl = new TestLock(); final Object object = new Object(); Thread t = new Thread(new Runnable(){ public void run() { synchronized(object) { try { object.wait(); } catch (Exception e) { e.printStackTrace(); } System.out.println("Last Value: " + tl.getLockValue()); System.out.println("线程-" + Thread.currentThread() + "获取到了锁！"); } } }); Thread t1 = new Thread(new Runnable(){ public void run() { synchronized(object) { try { object.wait(); } catch (Exception e) { e.printStackTrace(); } System.out.println("Last Value: " + tl.getLockValue()); System.out.println("线程-" + Thread.currentThread() + "获取到了锁！"); } } }); Thread t2 = new Thread(new Runnable(){ public void run() { synchronized(object) { tl.addLockValue(55.55); try { //单个线程则通知一个 //object.notify(); //多个线程则都能获得锁 object.notifyAll(); } catch (Exception e) { e.printStackTrace(); } System.out.println("线程-" + Thread.currentThread() + "调用了notify！"); System.out.println("线程-" + Thread.currentThread() + "释放了锁！"); } } }); t.start(); t1.start(); try { Thread.sleep(100); } catch(Exception e) { e.printStackTrace(); } t2.start(); } catch(Exception e) { e.printStackTrace(); } } } |
