java ThreadPoolExecutor 学习笔记
/**
* @param corePoolSize
* 线程池中保持的线程数量
* @param maximumPoolSize
* 线程池最大可开启线程数
* @param keepAliveTime
* 当线程池中的线程总量大于保持的线程数量时，
* 此参数设置其中空闲的线程将保持的时间数量
* @param unit
* 保持的时间单位
* 当其中的线程有空闲超过这个时间的，就将此线程杀死，
* 一直到线程池的保持线程量，此时间设置将不再起作用
* @param workQueue
* 线程池的等待队列
* 当需要执行的线程大于保持的线程数量时，会将此线程加入到这里设置的等待队列中
* @param threadFactory
* 线程工厂类 制定了此参数后可将Runnable实现类添加到execute方法中
* 缺省使用静态内部类DefaultThreadFactory
* @param handler
* 当线程的等待队列超出容量时 执行的处理程序
* 缺省使用静态内部类AbortPolicy
*/
public ThreadPoolExecutor(
int corePoolSize,
int maximumPoolSize,
long keepAliveTime,
TimeUnit unit,
BlockingQueue<Runnable> workQueue,
ThreadFactory threadFactory,
RejectedExecutionHandler handler){}
一、简单案例
1、Executors.newFixedThreadPool(int num)
特点：
固定线程池中可用线程数量，等待队列使用的是无界链表队列LinkedBlockingQueue，
源码：
public static ExecutorService newFixedThreadPool(int nThreads) {
return new ThreadPoolExecutor(nThreads, nThreads,
0L, TimeUnit.MILLISECONDS,
new LinkedBlockingQueue<Runnable>());
}
简单例子如下所示：
public static void jdkExecutor(){
ExecutorService exe = Executors.newFixedThreadPool(3);
for(int i=0;i<5;i++){
exe.execute(new Thread(new Runnable() {
@Override
public void run() {
System.err.println(Thread.currentThread().getName());
}
}));
}
}
//使用的是 线程的缺省 DefaultThreadFactory(静态内部类)线程工厂
public static void jdkExecutor2(){
ExecutorService exe = Executors.newFixedThreadPool(3);
for(int i=0;i<5;i++){
exe.execute(new Runnable() {
@Override
public void run() {
System.err.println(Thread.currentThread().getName());
}
});
}
}
//自定义线程工厂
public static void jdkExecutor3(){
ExecutorService exe = Executors.newFixedThreadPool(3,
new JdkFactory());
for(int i=0;i<5;i++){
exe.execute(new Runnable() {
@Override
public void run() {
System.err.println(Thread.currentThread().getName());
}
});
}
}
//自定义工厂
public static class JdkFactory implements ThreadFactory{
@Override
public Thread newThread(Runnable r) {
return new Thread( r);
}
}
运行结果如下所示(有三个线程在执行)：
pool-1-thread-1 pool-1-thread-3 pool-1-thread-2 pool-1-thread-3 pool-1-thread-1
2、Executors.newSingleThreadExecutor()
特点：
每一个任务都是使用同一个线程完成，等待队列使用的是无界链表队列LinkedBlockingQueue，
源码：
public static ExecutorService newSingleThreadExecutor() {
return new FinalizableDelegatedExecutorService
(new ThreadPoolExecutor(1, 1,
0L, TimeUnit.MILLISECONDS,
new LinkedBlockingQueue<Runnable>()));
}
简单例子如下所示：
public static void jdkExecutor(){
ExecutorService exe = Executors.newSingleThreadExecutor();
for(int i=0;i<5;i++){
exe.execute(new Thread(new Runnable() {
@Override
public void run() {
System.err.println(Thread.currentThread().getName());
}
}));
}
}
//线程工厂模式同上
运行结果如下所示：
pool-1-thread-1 pool-1-thread-1 pool-1-thread-1 pool-1-thread-1 pool-1-thread-1
3、ExecutorService newCachedThreadPool()
特点：
线程池中可用线程数量无限，等待队列使用的是同步队列SynchronousQueue，会有60秒时间等待是否让空闲线程关闭。
源码：
public static ExecutorService newCachedThreadPool() {
return new ThreadPoolExecutor(0, Integer.MAX_VALUE,
60L, TimeUnit.SECONDS,
new SynchronousQueue<Runnable>());
}
简单案例如下所示：
public static void jdkExecutor(){
ExecutorService exe = Executors.newCachedThreadPool();
for(int i=0;i<10;i++){
exe.execute(new Thread(new Runnable() {
@Override
public void run() {
System.err.println(Thread.currentThread().getName());
}
}));
}
}
//线程工厂模式同上
运行结果如下所示：
pool-1-thread-1 pool-1-thread-3 pool-1-thread-2 pool-1-thread-4 pool-1-thread-6 pool-1-thread-2 pool-1-thread-4 pool-1-thread-3 pool-1-thread-6 pool-1-thread-5
4、直接使用JDK ThreadPoolExecutor
简单案例如下所示：
public static void jdkBaseExecuter(){
ThreadPoolExecutor treadepool = new ThreadPoolExecutor(2, 4,60,
TimeUnit.SECONDS, new ArrayBlockingQueue<Runnable>(200),
new ErrorHandler());
for(int i=0;i<10;i++){
treadepool.execute(new Runnable() {
@Override
public void run() {
System.err.println(Thread.currentThread().getName());
}
});
}
}
//RejectedExecutionHandler缺省使用内部类AbortPolicy
private static class ErrorHandler implements RejectedExecutionHandler{
@Override
public void rejectedExecution(Runnable r,ThreadPoolExecutor executor) {
System.err.println("队列越界:"+executor.getQueue().size());
}
}
运行结果如下所示：
pool-1-thread-1 pool-1-thread-2 pool-1-thread-1 pool-1-thread-2 pool-1-thread-1 pool-1-thread-2 pool-1-thread-2 pool-1-thread-2 pool-1-thread-1 pool-1-thread-2
发现此时程序一直使用的是2个线程再执行任务，并未对保持线程数进行扩充。原因是因为此时有界缓存队列大小为200，未达到队列最大值，并不会重新开启新线程。将代码做如下改动：
ThreadPoolExecutor treadepool = new ThreadPoolExecutor(2, 4,60, TimeUnit.SECONDS,new ArrayBlockingQueue<Runnable>(6),new ErrorHandler());
运行结果将如下所示：
pool-1-thread-1 pool-1-thread-3 pool-1-thread-3 pool-1-thread-3 pool-1-thread-2 pool-1-thread-2 pool-1-thread-2 pool-1-thread-3 pool-1-thread-4 pool-1-thread-1
如果将有界队列值再缩小如下所示：
ThreadPoolExecutor treadepool = new ThreadPoolExecutor(2, 4,60, TimeUnit.SECONDS,new ArrayBlockingQueue<Runnable>(4),new ErrorHandler());
运行结果如下所示：
pool-1-thread-1 pool-1-thread-3 pool-1-thread-4 队列越界:4 pool-1-thread-2 pool-1-thread-4 pool-1-thread-4 pool-1-thread-3 pool-1-thread-1 pool-1-thread-2
就会出现队列越界错误，如果使用的是缺省ExecutionHandler将会初夏如下错误：
java.util.concurrent.RejectedExecutionException: Task xxxxxxx rejected from java.util.concurrent.ThreadPoolExecutor@56833a2e [Running, pool size = 4, active threads = 0, queued tasks = 0, completed tasks = 8] at java.util.concurrent.ThreadPoolExecutor$AbortPolicy.rejectedExecution(ThreadPoolExecutor.java:2048) at java.util.concurrent.ThreadPoolExecutor.reject(ThreadPoolExecutor.java:821) at java.util.concurrent.ThreadPoolExecutor.execute(ThreadPoolExecutor.java:1372)
所以对线程池的配置要慎重。
5、ThreadPoolTaskExecutor spring线程池
简单案例如下所示：
public static void springExecutor(){
ThreadPoolTaskExecutor taskExecutor = new ThreadPoolTaskExecutor();
//手动创建时需要进行初始化ThreadFactory 和RejectedExecutionHandler
taskExecutor.initialize();
taskExecutor.setCorePoolSize(2);
taskExecutor.setMaxPoolSize(4);
taskExecutor.setQueueCapacity(200);
for(int i=0;i<10;i++){
taskExecutor.execute(new Thread(new Runnable() {
@Override
public void run() {
System.err.println(Thread.currentThread().getName());
}
}));
}
}
当然ThreadPoolTaskExecutor 也可以在Spring的XML中进行定义，然后依赖注入进来，代码如下所示：
@Autowired private TaskExecutor taskExecutor; <bean id="taskExecutor" class= "org.springframework.scheduling.concurrent.ThreadPoolTaskExecutor"> <property name="corePoolSize" value="2" /> <property name="maxPoolSize" value="4" /> <property name="queueCapacity" value="200" /> </bean> 注：在基于Spring容器时不需要手工进行initialize初始化，交由Spring容器初始化
运行结果如下所示：
ThreadPoolTaskExecutor-1 ThreadPoolTaskExecutor-1 ThreadPoolTaskExecutor-1 ThreadPoolTaskExecutor-1 ThreadPoolTaskExecutor-2 ThreadPoolTaskExecutor-1 ThreadPoolTaskExecutor-2 ThreadPoolTaskExecutor-1 ThreadPoolTaskExecutor-2 ThreadPoolTaskExecutor-1
具体的参数配置同上
注：以上的各种队列的不同点将于下篇进行说明