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ExecutorService: Await Task Completion
ExecutorService is a handy tool for efficient task execution, but pausing until all tasks are complete can be tricky. Let's dive into a common issue and its practical solution.
Error in wait()
The quoted code snippet, which employs a fixed-thread-pool ExecutorService, experiences an IllegalMonitorStateException when attempting to use es.wait(). This occurs because wait() is intended for use with specific thread synchronization idioms, not with ExecutorService.
Simplest Solution: invokeAll()
ExecutorService offers a simpler alternative for this purpose: invokeAll(). This method takes a collection of Callable tasks, executes them in parallel, and blocks until all tasks are finished. Here's how to use it:
ExecutorService es = Executors.newFixedThreadPool(2); List<Callable<Object>> todo = new ArrayList<>(uniquePhrases.size()); for (DataTable singleTable: uniquePhrases) { todo.add(Executors.callable(new ComputeDTask(singleTable))); } List<Future<Object>> answers = es.invokeAll(todo);
invokeAll() returns a list of Future objects, each representing an individual task. Once all tasks are complete, accessing any Future's isDone() will return true.
Advantages of invokeAll()
Other Methods
Remember, invokeAll() requires your tasks to implement Callable. If ComputeDTask is a Runnable, wrap it as shown in the code snippet or utilize Executors.callable().
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