How to use the ExecutorCompletionService function in Java for thread pool task scheduling

With the development of Internet technology, the importance of multi-threaded programming has become increasingly prominent. When writing high-concurrency programs, making full use of multi-threading technology can greatly improve the execution efficiency of the program. However, multi-threaded programming itself involves many issues, such as communication between threads, synchronization cooperation, etc. In order to solve these problems, Java provides many thread pool frameworks, among which ExecutorCompletionService is one of them. This article will introduce the usage of ExecutorCompletionService and how to use this function for thread pool task scheduling.

1. Overview of ExecutorCompletionService

ExecutorCompletionService is an extension of the Executor framework in Java. It maintains a thread pool to execute a set of asynchronous tasks and saves the results of these tasks in a in queue. ExecutorCompletionService allows us to obtain results in completed tasks. ExecutorCompletionService provides a Futured94943c0b4933ad8cac500132f64757f submit(Callabled94943c0b4933ad8cac500132f64757f task) method and a Futured94943c0b4933ad8cac500132f64757f take() method. The former submits the task to the thread pool and returns the Future object, and the latter obtains the completed task from the queue. result.

The main advantage of ExecutorCompletionService is that it reduces the time waiting for all tasks to complete. When a task is completed, we can get its results immediately without waiting for all other tasks to complete. This way, we can process completed tasks as early as possible without having to wait for all tasks to complete before processing them. This method can effectively improve the execution efficiency of the program.

2. Usage of ExecutorCompletionService

When using ExecutorCompletionService, we need to first create an ExecutorService object. ExecutorService is a thread pool framework in Java that can maintain a set of threads to perform a series of tasks. We can use the factory method provided by the Executors class to create an ExecutorService object. The following is a sample code to create an ExecutorService object:

ExecutorService executor = Executors.newFixedThreadPool(10);

A thread pool of size 10 is created here.

Next, we create an ExecutorCompletionService object and use it to submit tasks to the thread pool:

ExecutorCompletionService<String> completionService = new ExecutorCompletionService<>(executor);
for (int i = 0; i < 10; i++) {
    final int taskId = i;
    completionService.submit(() -> {
        String result = doSomeTask(taskId);
        return result;
    });
}

Here, 10 tasks are submitted using a for loop, each task is a Callable type object. In this example, we use Lambda expressions to create Callable objects, which is a new feature introduced in Java 8.

In the submit method, we pass in a Callable object, execute a hypothetical "task" in this Callable object, and return a result. In actual business scenarios, actual data processing, network requests and other operations can be performed here.

After submitting the task, we can use the take method to obtain the results of the completed tasks:

for (int i = 0; i < 10; i++) {
    Future<String> future = completionService.take();
    String result = future.get();
    System.out.println("Task " + i + " result: " + result);
}

Here, a for loop is used to obtain the results of the completed tasks. Calling the take method can Get a Future object and use the get method to get the results of the task. Here the results are output to the console.

3. Performance tuning of the thread pool

In addition to using ExecutorCompletionService to simplify the process of task submission and result acquisition, we also need to consider the performance tuning of the thread pool. The number of threads in the thread pool and the size of the queue will have an impact on the performance of the program.

Directly increasing the number of threads will cause two problems: first, the context switching between threads will increase, which will affect the performance of the program; second, the threads in the thread pool can easily consume system resources, causing the system to The load is too high and problems such as OOM occur. Therefore, we need to adjust the size of the thread pool according to the actual business scenario.

The size of the queue directly affects the concurrent processing capability of the thread pool. If the size of the queue is too small, it will cause the thread pool to execute very fast and consume system resources quickly; if the size of the queue is too large, it will cause the thread pool to execute very slowly and cannot maintain the efficiency of the program. Therefore, we need to adjust the queue size according to the actual business scenario.

In short, thread pool performance tuning needs to be based on actual business scenarios. Simply increasing the size of the thread pool and the size of the queue does not guarantee the efficiency of the program. We need to make adjustments according to the actual situation.

4. Conclusion

This article introduces the usage of the ExecutorCompletionService function in Java and how to use this function for thread pool task scheduling. Through ExecutorCompletionService, we can submit tasks and obtain task execution results more conveniently, thereby improving program execution efficiency. At the same time, this article also briefly introduces the performance tuning of thread pools to help us better optimize our code.

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