Java：線程池（ExecutorService）使用源碼說明

轉自：https://blog.csdn.net/wanghao_0206/article/details/76460877

一、前提

/**
* 線程運行demo，運行時打出線程id以及傳入線程中參數
*/
public classThreadRunnerimplementsRunnable{
? ? private final SimpleDateFormat format = new SimpleDateFormat("HH:mm:ss.SSS");

? ? /**
? ? ?* 線程私有屬性，創建線程時創建
? ? ?*/
? ? private Integer num;
? ? public ThreadRunner(Integer num) {
? ? ? ? this.num = num;
? ? }

? ? @Override
? ? public void run() {
? ? ? ? System.out.println("thread:" + Thread.currentThread().getName() + ",time:" + format.format(new Date()) + ",num:" + num);

? ? ? ? try {//使線程睡眠，模擬線程阻塞情況
? ? ? ? ? ? TimeUnit.SECONDS.sleep(1);
? ? ? ? } catch (InterruptedException e) {
? ? ? ? ? ? e.printStackTrace();
? ? ? ? }
? ? }
}

二、分類

1、FixedThreadPool-有一個固定大小的線程池

public class FixedThreadPoolDemo {
? ? public static void main(String[] args) {
? ? ? ? ExecutorService pool = Executors.newFixedThreadPool(4);
? ? ? ? for(int i = 0 ; i < 50 ; i++){
? ? ? ? ? ? pool.submit(new ThreadRunner((i + 1)));
? ? ? ? }
? ? ? ? pool.shutdown();
? ? }
}

輸出：

thread:pool-1-thread-2,time:16:14:45.677,num:2
thread:pool-1-thread-4,time:16:14:45.678,num:4
thread:pool-1-thread-3,time:16:14:45.680,num:3
thread:pool-1-thread-1,time:16:14:45.684,num:1
thread:pool-1-thread-4,time:16:14:46.680,num:5
thread:pool-1-thread-2,time:16:14:46.680,num:6
thread:pool-1-thread-3,time:16:14:46.680,num:7
thread:pool-1-thread-1,time:16:14:46.684,num:8
thread:pool-1-thread-4,time:16:14:47.680,num:9
thread:pool-1-thread-2,time:16:14:47.680,num:10
thread:pool-1-thread-3,time:16:14:47.681,num:11
thread:pool-1-thread-1,time:16:14:47.684,num:12
thread:pool-1-thread-4,time:16:14:48.681,num:13
thread:pool-1-thread-2,time:16:14:48.681,num:14
thread:pool-1-thread-3,time:16:14:48.681,num:15
thread:pool-1-thread-1,time:16:14:48.684,num:16
thread:pool-1-thread-4,time:16:14:49.681,num:17
thread:pool-1-thread-2,time:16:14:49.682,num:18
thread:pool-1-thread-3,time:16:14:49.682,num:19
thread:pool-1-thread-1,time:16:14:49.684,num:20
thread:pool-1-thread-4,time:16:14:50.681,num:21
thread:pool-1-thread-2,time:16:14:50.682,num:22
thread:pool-1-thread-3,time:16:14:50.682,num:23
thread:pool-1-thread-1,time:16:14:50.684,num:24
thread:pool-1-thread-4,time:16:14:51.681,num:25
thread:pool-1-thread-2,time:16:14:51.682,num:26
thread:pool-1-thread-3,time:16:14:51.682,num:27
thread:pool-1-thread-1,time:16:14:51.684,num:28
thread:pool-1-thread-4,time:16:14:52.681,num:29
thread:pool-1-thread-2,time:16:14:52.682,num:30
thread:pool-1-thread-3,time:16:14:52.682,num:31
thread:pool-1-thread-1,time:16:14:52.684,num:32
thread:pool-1-thread-4,time:16:14:53.681,num:33
thread:pool-1-thread-2,time:16:14:53.682,num:34
thread:pool-1-thread-3,time:16:14:53.683,num:35
thread:pool-1-thread-1,time:16:14:53.685,num:36
thread:pool-1-thread-2,time:16:14:54.682,num:38
thread:pool-1-thread-4,time:16:14:54.682,num:37
thread:pool-1-thread-3,time:16:14:54.683,num:39
thread:pool-1-thread-1,time:16:14:54.686,num:40
thread:pool-1-thread-2,time:16:14:55.682,num:41
thread:pool-1-thread-4,time:16:14:55.682,num:42
thread:pool-1-thread-3,time:16:14:55.683,num:43
thread:pool-1-thread-1,time:16:14:55.686,num:44
thread:pool-1-thread-2,time:16:14:56.682,num:45
thread:pool-1-thread-4,time:16:14:56.683,num:46
thread:pool-1-thread-3,time:16:14:56.684,num:47
thread:pool-1-thread-1,time:16:14:56.686,num:48
thread:pool-1-thread-2,time:16:14:57.683,num:49
thread:pool-1-thread-4,time:16:14:57.683,num:50

總結：?

- 池中線程數量固定，不會發生變化?

- 使用無界的LinkedBlockingQueue，要綜合考慮生成與消費能力，生成過剩，可能導致堆內存溢出。?

- 適用一些很穩定很固定的正規并發線程，多用于服務器

2、CachedThreadPool

public class CachedThreadPoolDemo {
? ? public static void main(String[] args) {
? ? ? ? ExecutorService pool = Executors.newCachedThreadPool();
? ? ? ? for(int i = 0 ; i < 50 ; i++){
? ? ? ? ? ? pool.submit(new ThreadRunner((i + 1)));
? ? ? ? }
? ? ? ? pool.shutdown();
? ? }
}

輸出：

thread:pool-1-thread-2,time:16:17:21.289,num:2
thread:pool-1-thread-3,time:16:17:21.290,num:3
thread:pool-1-thread-4,time:16:17:21.290,num:4
thread:pool-1-thread-6,time:16:17:21.291,num:6
thread:pool-1-thread-7,time:16:17:21.291,num:7
thread:pool-1-thread-8,time:16:17:21.291,num:8
thread:pool-1-thread-1,time:16:17:21.292,num:1
thread:pool-1-thread-10,time:16:17:21.293,num:10
thread:pool-1-thread-5,time:16:17:21.294,num:5
thread:pool-1-thread-11,time:16:17:21.294,num:11
thread:pool-1-thread-15,time:16:17:21.294,num:15
thread:pool-1-thread-9,time:16:17:21.294,num:9
thread:pool-1-thread-16,time:16:17:21.295,num:16
thread:pool-1-thread-20,time:16:17:21.295,num:20
thread:pool-1-thread-14,time:16:17:21.296,num:14
thread:pool-1-thread-12,time:16:17:21.296,num:12
thread:pool-1-thread-19,time:16:17:21.297,num:19
thread:pool-1-thread-13,time:16:17:21.299,num:13
thread:pool-1-thread-17,time:16:17:21.300,num:17
thread:pool-1-thread-18,time:16:17:21.302,num:18
thread:pool-1-thread-22,time:16:17:21.304,num:22
thread:pool-1-thread-23,time:16:17:21.304,num:23
thread:pool-1-thread-24,time:16:17:21.305,num:24
thread:pool-1-thread-21,time:16:17:21.305,num:21
thread:pool-1-thread-26,time:16:17:21.305,num:26
thread:pool-1-thread-25,time:16:17:21.306,num:25
thread:pool-1-thread-29,time:16:17:21.307,num:29
thread:pool-1-thread-28,time:16:17:21.308,num:28
thread:pool-1-thread-30,time:16:17:21.308,num:30
thread:pool-1-thread-34,time:16:17:21.308,num:34
thread:pool-1-thread-35,time:16:17:21.308,num:35
thread:pool-1-thread-33,time:16:17:21.308,num:33
thread:pool-1-thread-27,time:16:17:21.309,num:27
thread:pool-1-thread-32,time:16:17:21.308,num:32
thread:pool-1-thread-31,time:16:17:21.309,num:31
thread:pool-1-thread-36,time:16:17:21.310,num:36
thread:pool-1-thread-37,time:16:17:21.310,num:37
thread:pool-1-thread-38,time:16:17:21.310,num:38
thread:pool-1-thread-42,time:16:17:21.310,num:42
thread:pool-1-thread-40,time:16:17:21.310,num:40
thread:pool-1-thread-41,time:16:17:21.311,num:41
thread:pool-1-thread-47,time:16:17:21.762,num:47
thread:pool-1-thread-43,time:16:17:21.762,num:43
thread:pool-1-thread-39,time:16:17:21.762,num:39
thread:pool-1-thread-45,time:16:17:21.762,num:45
thread:pool-1-thread-44,time:16:17:21.763,num:44
thread:pool-1-thread-46,time:16:17:21.761,num:46
thread:pool-1-thread-48,time:16:17:21.761,num:48
thread:pool-1-thread-49,time:16:17:21.765,num:49
thread:pool-1-thread-50,time:16:17:21.765,num:50

總結?

- 池中線程時隨著處理數據增加而增加?

- 線程數并不是一直增加，如果有新任務需要執行時，首先查詢池中是否有空閑線程并且還為到空閑截止時間，如果有，則使用空閑線程，如果沒有，則創建新線程并放入池中。?

- 用于執行一些生存期很短的異步型任務。不適用于IO等長延時操作，因為這可能會創建大量線程，導致系統崩潰。?

- 使用SynchronousQueue作為阻塞隊列，如果有新任務進入隊列，必須隊列中數據被其他線程處理，否則會等待。

3、SingleThreadExecutor

public class SingleThreadPoolDemo {
? ? public static void main(String[] args) {
? ? ? ? ExecutorService pool = Executors.newSingleThreadExecutor();
? ? ? ? for(int i = 0 ; i < 50 ; i++){
? ? ? ? ? ? pool.submit(new ThreadRunner((i + 1)));
? ? ? ? }
? ? ? ? pool.shutdown();
? ? }
}

輸出：

thread:pool-1-thread-1,time:16:20:10.194,num:1
thread:pool-1-thread-1,time:16:20:11.197,num:2
thread:pool-1-thread-1,time:16:20:12.197,num:3
thread:pool-1-thread-1,time:16:20:13.197,num:4
thread:pool-1-thread-1,time:16:20:14.197,num:5
thread:pool-1-thread-1,time:16:20:15.198,num:6
thread:pool-1-thread-1,time:16:20:16.198,num:7
thread:pool-1-thread-1,time:16:20:17.198,num:8
thread:pool-1-thread-1,time:16:20:18.198,num:9
thread:pool-1-thread-1,time:16:20:19.198,num:10
thread:pool-1-thread-1,time:16:20:20.198,num:11
thread:pool-1-thread-1,time:16:20:21.199,num:12
thread:pool-1-thread-1,time:16:20:22.200,num:13
thread:pool-1-thread-1,time:16:20:23.200,num:14
thread:pool-1-thread-1,time:16:20:24.200,num:15
thread:pool-1-thread-1,time:16:20:25.200,num:16
thread:pool-1-thread-1,time:16:20:26.201,num:17
thread:pool-1-thread-1,time:16:20:27.201,num:18
thread:pool-1-thread-1,time:16:20:28.201,num:19
thread:pool-1-thread-1,time:16:20:29.201,num:20
thread:pool-1-thread-1,time:16:20:30.202,num:21
thread:pool-1-thread-1,time:16:20:31.202,num:22
thread:pool-1-thread-1,time:16:20:32.203,num:23
thread:pool-1-thread-1,time:16:20:33.203,num:24
thread:pool-1-thread-1,time:16:20:34.203,num:25
thread:pool-1-thread-1,time:16:20:35.203,num:26
thread:pool-1-thread-1,time:16:20:36.203,num:27
thread:pool-1-thread-1,time:16:20:37.203,num:28
thread:pool-1-thread-1,time:16:20:38.203,num:29
thread:pool-1-thread-1,time:16:20:39.203,num:30
thread:pool-1-thread-1,time:16:20:40.203,num:31
thread:pool-1-thread-1,time:16:20:41.203,num:32
thread:pool-1-thread-1,time:16:20:42.203,num:33
thread:pool-1-thread-1,time:16:20:43.204,num:34
thread:pool-1-thread-1,time:16:20:44.204,num:35
thread:pool-1-thread-1,time:16:20:45.204,num:36
thread:pool-1-thread-1,time:16:20:46.204,num:37
thread:pool-1-thread-1,time:16:20:47.205,num:38
thread:pool-1-thread-1,time:16:20:48.205,num:39
thread:pool-1-thread-1,time:16:20:49.205,num:40
thread:pool-1-thread-1,time:16:20:50.206,num:41
thread:pool-1-thread-1,time:16:20:51.206,num:42
thread:pool-1-thread-1,time:16:20:52.207,num:43
thread:pool-1-thread-1,time:16:20:53.207,num:44
thread:pool-1-thread-1,time:16:20:54.207,num:45
thread:pool-1-thread-1,time:16:20:55.207,num:46
thread:pool-1-thread-1,time:16:20:56.207,num:47
thread:pool-1-thread-1,time:16:20:57.208,num:48
thread:pool-1-thread-1,time:16:20:58.208,num:49
thread:pool-1-thread-1,time:16:20:59.209,num:50

總結：?

- 線程中只有一個線程在執行?

- 適用于有明確執行順序但是不影響主線程的任務，壓入池中的任務會按照隊列順序執行。?

- 使用無界的LinkedBlockingQueue，要綜合考慮生成與消費能力，生成過剩，可能導致堆內存溢出。

三、源碼

public static ExecutorService newFixedThreadPool(int nThreads) {
? ? ? ? return new ThreadPoolExecutor(nThreads, nThreads,
? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? 0L, TimeUnit.MILLISECONDS,
? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? new LinkedBlockingQueue());

public static ExecutorService newCachedThreadPool() {
? ? ? ? return new ThreadPoolExecutor(0, Integer.MAX_VALUE,
? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? 60L, TimeUnit.SECONDS,
? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? new SynchronousQueue());

public static ExecutorService newSingleThreadExecutor() {
? ? ? ? return new FinalizableDelegatedExecutorService
? ? ? ? ? ? (new ThreadPoolExecutor(1, 1,
? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? 0L, TimeUnit.MILLISECONDS,
? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? new LinkedBlockingQueue()));
? ? }

* ThreadPoolExecutor 構造方法*

public ThreadPoolExecutor(int corePoolSize,
? ? ? ? ? ? ? ? ? ? ? ? ? int maximumPoolSize,
? ? ? ? ? ? ? ? ? ? ? ? ? long keepAliveTime,
? ? ? ? ? ? ? ? ? ? ? ? ? TimeUnit unit,
? ? ? ? ? ? ? ? ? ? ? ? ? BlockingQueue workQueue) {
? ? this(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue,
? ? ? ? ?Executors.defaultThreadFactory(), defaultHandler);
}

public ThreadPoolExecutor(int corePoolSize,
? ? ? ? ? ? ? ? ? ? ? ? ? int maximumPoolSize,
? ? ? ? ? ? ? ? ? ? ? ? ? long keepAliveTime,
? ? ? ? ? ? ? ? ? ? ? ? ? TimeUnit unit,
? ? ? ? ? ? ? ? ? ? ? ? ? BlockingQueue workQueue,
? ? ? ? ? ? ? ? ? ? ? ? ? ThreadFactory threadFactory,
? ? ? ? ? ? ? ? ? ? ? ? ? RejectedExecutionHandler handler) {

? ? if (corePoolSize < 0 ||
? ? ? ? maximumPoolSize <= 0 ||
? ? ? ? maximumPoolSize < corePoolSize ||
? ? ? ? keepAliveTime < 0)
? ? ? ? throw new IllegalArgumentException();
? ? if (workQueue == null || threadFactory == null || handler == null)
? ? ? ? throw new NullPointerException();
? ? this.corePoolSize = corePoolSize;
? ? this.maximumPoolSize = maximumPoolSize;
? ? this.workQueue = workQueue;
? ? this.keepAliveTime = unit.toNanos(keepAliveTime);
? ? this.threadFactory = threadFactory;
? ? this.handler = handler;
}

corePoolSize:線程池核心線程數量?

如果池中線程數量少于核心線程池數量，則直接新建線程處理當前任務。

核心線程池空閑不會被回收。

當池中無空閑線程時，新任務將被添加到阻塞隊列

maximumPoolSize：線程池最大線程數量?

當阻塞隊列已滿，并且有新任務還在入隊時，創建新的線程處理，直到線程數大于maximumPoolSize。

超出corePoolSize部分的線程超過空閑時間后會被回收

當線程已經超出corePoolSize，并且隊列容量已滿，則拒絕入隊。

keepAliveTime unit：線程存活時間?

當線程超出corePoolSize時生效

線程空余keepAliveTime后，將被回收

workQueue：線程使用阻塞隊列

threadFactory：創建線程池工廠?

用于控制創建線程或者銷毀線程時加入其它邏輯

handler：線程池拒絕策略?

直接丟棄（DiscardPolicy）

丟棄隊列中最老的任務(DiscardOldestPolicy)。

拋異常(AbortPolicy)

將任務分給調用線程來執行(CallerRunsPolicy)

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