java - 修复线程池: pause until thread available?

Question

这个问题已经有答案了:

How to make ThreadPoolExecutor's submit() method block if it is saturated? (16 个回答)

已关闭 6 年前。

我正在开发一个基于 Java 的程序，该程序从文件中读取并将每一行发送到其自己的处理 Runnable 中以执行一些单线程计算。我使用一个固定的线程池，每个可用核心一个任务，来并行化它。该文件很大，提交作业时不可能将每个文件加载到内存中。是否可以让主线程(正在提交这些任务)暂停，直到线程池中的线程变得可用？

Answer 1

创建一个简单的线程池，其可用工作线程与池大小相同。在提交之前检查是否存在可用线程，然后提交，否则等待锁定。

您还可以使用信号量，它会阻塞直到 acquire() 获得一些值。信号量示例:

Semaphore semaphore = new Semaphore(pool_size);

//critical section
semaphore.acquire();

...

semaphore.release();

简单线程池示例:

    private List<WorkerThread> workers;
        private LinkedList<WorkerThread> availWorkers = new LinkedList<WorkerThread>();
        private LinkedList<WorkerThread> busyWorkers = new LinkedList<WorkerThread>(); 

提交方式

   public boolean submit(Runnable runnable) {
            if (runnable == null) {
                return false;
            }

            synchronized (Lock) {

                handoffPending = true;

                // Wait until a worker thread is available
                while ((availWorkers.size() < 1) && !isShutdown) {
                    try {
                        Lock.wait(500);
                    } catch (InterruptedException ignore) {
                    }
                }

                if (!isShutdown) {
                    WorkerThread wt = (WorkerThread)availWorkers.removeFirst();
                    busyWorkers.add(wt);
                    wt.run(runnable);
                } else {
                    // If the thread pool is going down, execute the Runnable
                    // within a new additional worker thread (no thread from the pool).
                    WorkerThread wt = new WorkerThread(this, threadGroup,
                            "WorkerThread-LastJob", prio, isMakeThreadsDaemons(), runnable);
                    busyWorkers.add(wt);
                    workers.add(wt);
                    wt.start();
                }
                Lock.notifyAll();

            }

            return true;
        }