同步代码块
基本语句
synchronized (任意对象) {
操作共享代码
}
代码示例
public class SellTicket implements Runnable {
private int tickets = 100;
private Object object = new Object();
@Override
public void run() {
while (true) {
synchronized (object) {
if (tickets > 0) {
try {
Thread.sleep(100);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println(Thread.currentThread().getName() + "正在出售第" + tickets + "张票");
tickets--;
}
}
}
}
public static void main(String[] args) {
SellTicket sellTicket = new SellTicket();
Thread thread1 = new Thread(sellTicket, "窗口1");
Thread thread2 = new Thread(sellTicket, "窗口2");
Thread thread3 = new Thread(sellTicket, "窗口3");
thread1.start();
thread2.start();
thread3.start();
}
}
优缺点：
- 解决了多线程的数据安全问题
- 多线程时，每个线程都会判断同步上的锁，耗费资源，降低了程序的运行效率
同步方法
同步方法：将synchronized关键字加到方法上
- 格式: 修饰符 synchronized 返回值类型 方法名(){ }
- 同步方法的锁对象是this
同步静态方法，就是把synchronized关键字加到静态方法上
- 格式: 修饰符 static synchronized 返回值类型 方法名(){ }
- 同步静态方法的锁对象是 类名.class
代码示例
public class SellTicket implements Runnable {
// private int tickets = 100;
private static int tickets = 100;
private Object object = new Object();
private int x = 0;
@Override
public void run() {
while (true) {
if (x % 2 == 0) {
// synchronized (object) {
// synchronized (this) {
synchronized (SellTicket.class) {
if (tickets > 0) {
try {
Thread.sleep(100);
} catch (InterruptedException e) {
e.printStackTrace();
} System.out.println(Thread.currentThread().getName() + "正在出售第" + tickets + "张票");
tickets--;
}
}
} else {
// synchronized (object) {
// if (tickets > 0) {
// try {
// Thread.sleep(100);
// } catch (InterruptedException e) {
// e.printStackTrace();
// }
// System.out.println(Thread.currentThread().getName() + "正在出售第" + tickets + "张票");
// tickets--;
// }
// }
sellTicket();
}
x++;
}
}
// private void sellTicket(){
// synchronized (object) {
// if (tickets > 0) {
// try {
// Thread.sleep(100);
// } catch (InterruptedException e) {
// e.printStackTrace();
// }
// System.out.println(Thread.currentThread().getName() + "正在出售第" + tickets + "张票");
// tickets--;
// }
// }
// }
// private synchronized void sellTicket(){
// if (tickets > 0) {
// try {
// Thread.sleep(100);
// } catch (InterruptedException e) {
// e.printStackTrace();
// }
// System.out.println(Thread.currentThread().getName() + "正在出售第" + tickets + "张票");
// tickets--;
// }
private static synchronized void sellTicket(){
if (tickets > 0) {
try {
Thread.sleep(100);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println(Thread.currentThread().getName() + "正在出售第" + tickets + "张票");
tickets--;
}
}
public static void main(String[] args) {
SellTicket sellTicket = new SellTicket();
Thread thread1 = new Thread(sellTicket, "窗口1");
Thread thread2 = new Thread(sellTicket, "窗口2");
Thread thread3 = new Thread(sellTicket, "窗口3");
thread1.start();
thread2.start();
thread3.start();
}
}
lock锁
lock实现提供比使用synchronized方法和语句可获得更广泛的操作
- void lock()获得锁
- void unlock()释放
lock是接口不能直接实例化，采用实现类实例化ReentrantLock
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
public class SellTicket implements Runnable {
private int tickets = 100;
private Object object = new Object();
private Lock lock = new ReentrantLock();
@Override
public void run() {
while (true) {
try {
lock.lock();
if (tickets > 0) {
try {
Thread.sleep(100);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println(Thread.currentThread().getName() + "正在出售第" + tickets + "张票");
tickets--;
}
} finally {
lock.unlock();
}
}
}
public static void main(String[] args) {
SellTicket sellTicket = new SellTicket();
Thread thread1 = new Thread(sellTicket, "窗口1");
Thread thread2 = new Thread(sellTicket, "窗口2");
Thread thread3 = new Thread(sellTicket, "窗口3");
thread1.start();
thread2.start();
thread3.start();
}
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