Java语言ReadWriteLock特性实例测试
本文研究的主要是ReadWriteLock特性，具体如下。
ReadWriteLock几点特性
readLock与readLock不互斥
readLock与writeLock互斥
writeLock与readLock互斥
writeLock与writeLock互斥
举例来说:
线程1,先拿到readLock,线程2试图拿readLock,可以拿到
线程1,先拿到readLock,线程2试图拿writeLock,阻塞等待,直到线程1释放锁之后才可以拿到
线程1,先拿到writeLock,线程2试图拿readLock,阻塞等待,直到线程1释放锁之后才可以拿到
线程1,先拿到writeLock,线程2试图拿writeLock,阻塞等待,直到线程1释放锁之后才可以拿到
测试代码
packagecom.alioo.lock;
importjava.text.SimpleDateFormat;
importjava.util.Date;
importjava.util.concurrent.locks.Lock;
importjava.util.concurrent.locks.ReadWriteLock;
importjava.util.concurrent.locks.ReentrantReadWriteLock;
/**
*
*/
publicclassReadWriteLockDemo{
staticSimpleDateFormatsdf=newSimpleDateFormat("yyyy-MM-ddHH:mm:ss.SSS");
publicstaticvoidmain(String[]args){
Datadata=newData();
Workert1=newWorker(data,false);
//写
Workert2=newWorker(data,true);
//读
Workert3=newWorker(data,true);
//读
t1.start();
t2.start();
t3.start();
}
staticclassWorkerextendsThread{
Datadata;
Booleanread;
publicWorker(Datadata,Booleanread){
this.data=data;
this.read=read;
}
publicvoidrun(){
if(read)
data.read();else
data.write();
}
}
staticclassData{
ReadWriteLocklock=newReentrantReadWriteLock();
Lockread=lock.readLock();
Lockwrite=lock.writeLock();
publicvoidwrite(){
try{
Thread.sleep(2000);
//
}
catch(Exceptione){
}
write.lock();
System.out.println(Thread.currentThread()+"write:begin"
+sdf.format(newDate()));
try{
Thread.sleep(5000);
//
}
catch(Exceptione){
}
finally{
System.out.println(Thread.currentThread()+"write:end"
+sdf.format(newDate()));
write.unlock();
}
}
publicintread(){
read.lock();
System.out.println(Thread.currentThread()+"read:begin"
+sdf.format(newDate()));
try{
Thread.sleep(5000);
//
}
catch(Exceptione){
}
finally{
System.out.println(Thread.currentThread()+"read:end"
+sdf.format(newDate()));
read.unlock();
}
return1;
}
}
}
测试结果:
Thread[Thread-2,5,main]read:begin2018-01-2213:54:16.794
Thread[Thread-1,5,main]read:begin2018-01-2213:54:16.794
Thread[Thread-2,5,main]read:end2018-01-2213:54:21.795
Thread[Thread-1,5,main]read:end2018-01-2213:54:21.795
Thread[Thread-0,5,main]write:begin2018-01-2213:54:21.795
Thread[Thread-0,5,main]write:end2018-01-2213:54:26.795
测试结果解读:
同时启动了3个线程,其中1号线程Thread[Thread-0,5,main],执行write时先休眠了2秒.那么2,3号线程Thread[Thread-1,5,main],Thread[Thread-2,5,main]将会优先执行代码
read.lock();
由于read.lock();是不互斥的(即可重入的),所以他们同时拿到了锁,通过日志可以看出来
Thread[Thread-2,5,main]read:begin2018-01-2213:54:16.794 Thread[Thread-1,5,main]read:begin2018-01-2213:54:16.794
而且他们执行的时间开销是相同的(测试代码中都是休眠5秒),所以也将同时执行结束
Thread[Thread-2,5,main]read:end2018-01-2213:54:21.795 Thread[Thread-1,5,main]read:end2018-01-2213:54:21.795
只有当所有的readLock被释放掉之后,writeLock才能拿到锁,而这个时候Thread[Thread-1,5,main],Thread[Thread-2,5,main]执行结束后就会释放锁readLock
所以Thread[Thread-0,5,main]这个时候拿到了writeLock并执行自己的业务代码
Thread[Thread-0,5,main]write:begin2018-01-2213:54:21.795 Thread[Thread-0,5,main]write:end2018-01-2213:54:26.795
总结
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