1 原始构成
synchronized是关键字属于JVM层面, monitorenter(底层是通过monitor对象来完成,其wait/notify 等方法也依赖于monitor对象只有在同步块或方法中才能调wait/notify等方法) monitorexit
Lock是具体类(java.util.concurrent.locks.Lock)是api层面的锁
2 使用方法
synchronized不需要用户去手动释放锁,当synchronized 代码执行完后系统会自动让线程释放对锁的占用
ReentrantLock则需要用户去手动释放锁若没有主动释放锁,就有可能导致出现死锁现象。
需要Lock()和unLock()方法配合try/finally语句块来完成。
3 等待是否可中断
synchronized不可中断,除非抛出异常或者正常运行完成
ReentrantLock可中断
- 设置超时方法tryLock(long timeout, TimeUnit unit)
- lockInterruptibly()放代码块中,调用interrupt() 方法可中断
4 加锁是否公平
synchronized非公平锁
ReentrantLock两者都可以,默认非公平锁,构造方法可以传入boolean值,true 为公平锁,false为非公平锁
5 锁绑定多个条f件condition
synchronized没有
ReentrantLock用来实现分组唤醒需要唤醒的线程们,可以精确唤醒,而不是像synchronized要么随机唤醒一个线程 要么唤醒全部线程。 案例: A->B->C三个线程 依次打印 A打5次 B打10次 C打15次 循环打印10次
public class Demo16 {
public static void main(String[] args) throws InterruptedException {
Share share = new Share();
new Thread(() -> {
for (int i = 0; i < 10; i++) {
try {
share.aPrint5();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}, "AA").start();
new Thread(() -> {
for (int i = 0; i < 10; i++) {
try {
share.bPrint10();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}, "BB").start();
new Thread(() -> {
for (int i = 0; i < 10; i++) {
try {
share.cPrint15();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}, "CC").start();
}
}
class Share {
private Integer number = 1;
private Lock lock = new ReentrantLock();
private Condition c1 = lock.newCondition();
private Condition c2 = lock.newCondition();
private Condition c3 = lock.newCondition();
public void aPrint5() throws InterruptedException {
lock.lock();
try {
while (number != 1) {
c1.await();
}
for (int i = 0; i < 5; i++) {
System.out.println(Thread.currentThread().getName());
}
number = 2;
c2.signal();
}finally {
lock.unlock();
}
}
public void bPrint10() throws InterruptedException {
lock.lock();
try {
while (number != 2) {
c2.await();
}
for (int i = 0; i < 10; i++) {
System.out.println(Thread.currentThread().getName());
}
number = 3;
c3.signal();
}finally {
lock.unlock();
}
}
public void cPrint15() throws InterruptedException {
lock.lock();
try {
while (number != 3) {
c3.await();
}
for (int i = 0; i < 15; i++) {
System.out.println(Thread.currentThread().getName());
}
number = 1;
c1.signal();
}finally {
lock.unlock();
}
}
}