Java線程池參數詳解

一、核心參數

1、corePoolSize

核心池的大小，即線程池維護線程的最少數量。當提交一個任務到線程池時，線程池會創建一個線程來執行任務，即使其他線程處於空閑狀態。如果池中的線程數達到corePoolSize後，新提交的任務將被放入隊列中等待。如果隊列已滿，且池中的線程數小於maximumPoolSize，則創建新的線程執行任務。如果池中的線程數達到maximumPoolSize，則根據設置的拒絕策略來處理任務。

ThreadPoolExecutor threadPoolExecutor = new ThreadPoolExecutor(corePoolSize, maximumPoolSize, keepAliveTime, TimeUnit.SECONDS, new LinkedBlockingQueue<Runnable>());

2、maximumPoolSize

線程池最大數量。當線程池中的線程數目達到這個數目時，新的任務會被放入隊列中等待。如果隊列滿了，調用者就必須自己處理這個任務。如果使用無界的任務隊列這個參數就沒有任何作用。

ThreadPoolExecutor threadPoolExecutor = new ThreadPoolExecutor(corePoolSize, maximumPoolSize, keepAliveTime, TimeUnit.SECONDS, new LinkedBlockingQueue<Runnable>());

3、keepAliveTime

線程池中工作線程空閑後，保持存活的時間。

ThreadPoolExecutor threadPoolExecutor = new ThreadPoolExecutor(corePoolSize, maximumPoolSize, keepAliveTime, TimeUnit.SECONDS, new LinkedBlockingQueue<Runnable>());

二、任務隊列參數

1、workQueue

任務隊列，用來存儲等待執行的任務。常用的有四種隊列：

// 線程池中任務隊列為SynchronousQueue
ThreadPoolExecutor threadPoolExecutor1 = new ThreadPoolExecutor(corePoolSize, maximumPoolSize, keepAliveTime,
            TimeUnit.SECONDS, new SynchronousQueue<Runnable>());

// 線程池中任務隊列為LinkedBlockingQueue
ThreadPoolExecutor threadPoolExecutor2 = new ThreadPoolExecutor(corePoolSize, maximumPoolSize, keepAliveTime,
            TimeUnit.SECONDS, new LinkedBlockingQueue<Runnable>());

// 線程池中任務隊列為ArrayBlockingQueue
ThreadPoolExecutor threadPoolExecutor3 = new ThreadPoolExecutor(corePoolSize, maximumPoolSize, keepAliveTime,
            TimeUnit.SECONDS, new ArrayBlockingQueue<Runnable>(100));

// 線程池中任務隊列為PriorityBlockingQueue
ThreadPoolExecutor threadPoolExecutor4 = new ThreadPoolExecutor(corePoolSize, maximumPoolSize, keepAliveTime,
            TimeUnit.SECONDS, new PriorityBlockingQueue<Runnable>());

2、capacity

任務隊列的容量。如果任務數量達到這個值，新提交的任務將會被拒絕，並根據設置的拒絕策略來處理任務。

// 容量為100的有界隊列
ThreadPoolExecutor threadPoolExecutor = new ThreadPoolExecutor(corePoolSize, maximumPoolSize, keepAliveTime,
            TimeUnit.SECONDS, new ArrayBlockingQueue<Runnable>(100));

三、超時策略參數

1、allowCoreThreadTimeOut

該屬性為true時，表示樣品允許為核心線程設置超時時間，即當線程數大於核心線程數時，核心線程也會參與超時檢查。

ThreadPoolExecutor threadPoolExecutor = new ThreadPoolExecutor(corePoolSize, maximumPoolSize, keepAliveTime, TimeUnit.SECONDS, new LinkedBlockingQueue<Runnable>());
threadPoolExecutor.allowCoreThreadTimeOut(true);

2、rejectedExecutionHandler

當線程池中的資源已經全部使用，添加新線程被拒絕時，會進行拒絕處理。常用的拒絕策略有四種：

// 拒絕策略為AbortPolicy
ThreadPoolExecutor threadPoolExecutor1 = new ThreadPoolExecutor(corePoolSize, maximumPoolSize, keepAliveTime,
            TimeUnit.SECONDS, new LinkedBlockingQueue<Runnable>(), new ThreadPoolExecutor.AbortPolicy());

// 拒絕策略為DiscardPolicy
ThreadPoolExecutor threadPoolExecutor2 = new ThreadPoolExecutor(corePoolSize, maximumPoolSize, keepAliveTime,
            TimeUnit.SECONDS, new LinkedBlockingQueue<Runnable>(), new ThreadPoolExecutor.DiscardPolicy());

// 拒絕策略為DiscardOldestPolicy
ThreadPoolExecutor threadPoolExecutor3 = new ThreadPoolExecutor(corePoolSize, maximumPoolSize, keepAliveTime,
            TimeUnit.SECONDS, new LinkedBlockingQueue<Runnable>(), new ThreadPoolExecutor.DiscardOldestPolicy());

// 拒絕策略為CallerRunsPolicy
ThreadPoolExecutor threadPoolExecutor4 = new ThreadPoolExecutor(corePoolSize, maximumPoolSize, keepAliveTime,
            TimeUnit.SECONDS, new LinkedBlockingQueue<Runnable>(), new ThreadPoolExecutor.CallerRunsPolicy());

四、線程池擴展參數

1、ThreadFactory

通過ThreadFactory方式自定義線程池中的線程對象，可以自定義線程的名字、是否為守護線程等。

ThreadPoolExecutor threadPoolExecutor = new ThreadPoolExecutor(corePoolSize, maximumPoolSize, keepAliveTime, TimeUnit.SECONDS, new LinkedBlockingQueue<Runnable>(), new ThreadFactory() {
    private final AtomicInteger atomicInteger = new AtomicInteger(0);
    public Thread newThread(Runnable r) {
        Thread thread = new Thread(r);
        thread.setName("Thread-" + atomicInteger.getAndIncrement());
        return thread;
    }
});

2、beforeExecute和afterExecute

在每個任務之前和之後執行的操作。可以用來統計任務的執行時間等。

ThreadPoolExecutor threadPoolExecutor = new ThreadPoolExecutor(corePoolSize, maximumPoolSize, keepAliveTime, TimeUnit.SECONDS, new LinkedBlockingQueue<Runnable>(), new ThreadPoolExecutor.AbortPolicy());
threadPoolExecutor.setThreadFactory(new ThreadFactory() {
    private final AtomicInteger atomicInteger = new AtomicInteger(0);
    public Thread newThread(Runnable r) {
        Thread thread = new Thread(r);
        thread.setName("Thread-" + atomicInteger.getAndIncrement());
        return thread;
    }
});
// 執行任務前處理
threadPoolExecutor.prestartAllCoreThreads();
threadPoolExecutor.execute(() -> {
    // 任務執行時間統計
    long startTime = System.currentTimeMillis();
    try {
        // 執行任務
    } finally {
        // 任務執行時間統計
        long endTime = System.currentTimeMillis();
        log.info("任務執行時間: " + (endTime - startTime) + " ms");
    }
});

五、總結

本文主要對Java線程池中的主要參數進行了詳細的闡述，包括核心參數、任務隊列參數、超時策略參數以及線程池擴展參數。在使用線程池時，需要根據具體業務場景選擇合適的參數配置，避免線程池資源浪費或者任務無法及時執行的情況。