问题
Below code creates large number of runnable object in loop, even only 5 treads are there to process the tasks. Is there any way so that at any moment only 5 runnable object will be present in memory not the total number of tasks( 100000).
ExecutorService executor = Executors.newFixedThreadPool(5);
for (int i = 0; i < 10000; i++) {
Runnable worker = new WorkerThread("" + i);
System.out.println("ExecutorExample.main()");
executor.execute(worker);
}
回答1:
The requirement that at any moment only 5 runnable object will be present in memory is too restrictive. When a task finishes, there would be no next task to run, and some time would be spend to create another task. Better to have 5 runnung tasks and 5 waiting in a line. In order to restrict the number of the tasks in the queue, use a BlockingQueue of fixed size for runnables, e.g.
ThreadPoolExecutor executor = new ThreadPoolExecutor(
5, 5,
10L, TimeUnit.MILLISECONDS,
new LinkedBlockingQueue<Runnable>(5)
)
UPDT To avoid RejectedExecutionException, add RejectedExecutionHandler, as proposed in https://stackoverflow.com/a/3518588/1206301:
RejectedExecutionHandler block = new RejectedExecutionHandler() {
@Override
public void rejectedExecution(Runnable r, ThreadPoolExecutor executor) {
try {
executor.getQueue().put(r);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
};
executor.setRejectedExecutionHandler(block);
来源：https://stackoverflow.com/questions/44924429/best-practice-for-executing-large-number-of-tasks