Java ThreadPoolExecutor
ThreadPoolExecutor 且使用如下构造方法：
public ThreadPoolExecutor(int corePoolSize,
int maximumPoolSize,
long keepAliveTime,
TimeUnit unit,
BlockingQueue<Runnable> workQueue,
ThreadFactory threadFactory,
RejectedExecutionHandler handler)
如上使用一些初始化参数构建 ThreadPoolExecutor：
- corePoolSize - 线程池中保存的线程数，线程池不会 prefill 线程，不管线程池中是否有空闲线程，当线程数大小小于 corePoolSize 就新建线程
- maximumPoolSize - 线程池允许的最大线程数
- keepAliveTime - 当线程池中线程数大于 corePoolSize 时，多余的线程在等待空闲时间 keepAliveTime 后终止
- unit - keepAliveTime 的时间单位
- workQueue - Task 被执行之前首先至于此 workQueue，当然 workQueue 只保存实现 Runnable 的 Task，通常被 execute 方法提交
- threadFactory - 用来创建创建新线程
- handler - 当队列里累积的 Task 多于 workQueue 最大容量时用来处理新来的 Task
NOTE: 线程池并不会 prefill 线程，当
corePoolSize> 0 时，线程池不会自动关闭
示例
使用如下代码初始化一个 ThreadPoolExecutor:
ThreadPoolExecutor executor = new ThreadPoolExecutor(8, 8, 30, TimeUnit.SECONDS, new LinkedBlockingQueue<Runnable>(), new ThreadFactory(){
private final int id = executorSeq.getAndIncrement();
private final AtomicInteger threadSeq = new AtomicInteger(1);
public Thread newThread(Runnable r) {
return doPrivileged(new ThreadAction(r, id, threadSeq));
}}, POLICY);
示例.1 执行 PrintTask
执行 10 个 PrintTask:
for(int i = 0 ; i < 10 ; i ++) {
executor.execute(new PrintTask());
}
执行完成之后，ThreadPool 的状态: [Running, pool size = 8, active threads = 0, queued tasks = 0, completed tasks = 10]
ThreadPool 中所有线程处于 waiting on condition 状态:
"MSC service thread 1-8" #16 prio=5 os_prio=0 tid=0x00007f20c40ec800 nid=0x2780 waiting on condition [0x00007f209dce3000]
java.lang.Thread.State: WAITING (parking)
at sun.misc.Unsafe.park(Native Method)
- parking to wait for <0x00000000d7f80410> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:2039)
at java.util.concurrent.LinkedBlockingQueue.take(LinkedBlockingQueue.java:442)
at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1067)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1127)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at java.lang.Thread.run(Thread.java:745)
Locked ownable synchronizers:
- None
NOTE: 线程处于 waiting on condition 状态是因为 LinkedBlockingQueue 中没有 Runnable Task。
示例.2 执行 WaitTask
执行 10 个 WaitTask:
for(int i = 0 ; i < 10 ; i ++) {
executor.execute(new WaitTask());
}
执行完成之后，ThreadPool 的状态: [Running, pool size = 8, active threads = 8, queued tasks = 2, completed tasks = 0]
NOTE: queued tasks is 2, that’s due to ThreadPool’s maximumPoolSize is 8 and previous 8 threads are in wait.
ThreadPool 中所有线程处于 Object.wait() 状态:
"MSC service thread 1-8" #16 prio=5 os_prio=0 tid=0x00007f8f180f5000 nid=0x2823 in Object.wait() [0x00007f8ee56d1000]
java.lang.Thread.State: WAITING (on object monitor)
at java.lang.Object.wait(Native Method)
- waiting on <0x00000000d7f8fae8> (a org.wildfly.example.threads.MSCThreadPoolExecutor$WaitTask)
at java.lang.Object.wait(Object.java:502)
at org.wildfly.example.threads.MSCThreadPoolExecutor$WaitTask.run(MSCThreadPoolExecutor.java:55)
- locked <0x00000000d7f8fae8> (a org.wildfly.example.threads.MSCThreadPoolExecutor$WaitTask)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at java.lang.Thread.run(Thread.java:745)
Locked ownable synchronizers:
- <0x00000000d7f8faf8> (a java.util.concurrent.ThreadPoolExecutor$Worker)