一、一個線程池中的線程異常了,那麼線程池會怎麼處理這個線程?
需要說明,本文的線程池都是java.util.concurrent.ExecutorService線程池,本文將圍繞驗證,閱讀源碼倆方面來解析這個問題。
二、代碼驗證
2.1 驗證execute提交線程池中
2.1.1 測試代碼:
public class ThreadPoolExecutorDeadTest {
public static void main(String[] args) throws InterruptedException {
ExecutorService executorService = buildThreadPoolExecutor();
executorService.execute(() -> exeTask("execute"));
executorService.execute(() -> exeTask("execute"));
executorService.execute(() -> exeTask("execute-exception"));
executorService.execute(() -> exeTask("execute"));
executorService.execute(() -> exeTask("execute"));
Thread.sleep(5000);
System.out.println("再次執行任務=======================");
executorService.execute(() -> exeTask("execute"));
executorService.execute(() -> exeTask("execute"));
executorService.execute(() -> exeTask("execute"));
executorService.execute(() -> exeTask("execute"));
executorService.execute(() -> exeTask("execute"));
}
public static ExecutorService buildThreadPoolExecutor() {
return new ThreadPoolExecutor(5, 10, 30, TimeUnit.SECONDS,
new LinkedBlockingQueue<>(1000), new ThreadFactoryBuilder().setNameFormat("test-%s").build()
, new ThreadPoolExecutor.CallerRunsPolicy());
}
private static void exeTask(String name) {
String printStr = "[thread-name:" + Thread.currentThread().getName() + ",執行方式:" + name + "]";
if ("execute-exception".equals(name)) {
throw new RuntimeException(printStr + ", 我拋異常了");
} else {
System.out.println(printStr);
}
}
}
2.1.2 執行結果如下:
2.1.3 結論:
execute 提交到線程池的方式,如果執行中拋出異常,並且沒有在執行邏輯中catch,那麼會拋出異常,並且移除拋出異常的線程,創建新的線程放入到線程池中。
2.2 驗證submit提交線程池中
2.2.1 測試代碼:
public class ThreadPoolExecutorDeadTest {
public static void main(String[] args) throws InterruptedException {
ExecutorService executorService = buildThreadPoolExecutor();
executorService.submit(() -> exeTask("execute"));
executorService.submit(() -> exeTask("execute"));
executorService.submit(() -> exeTask("execute-exception"));
executorService.submit(() -> exeTask("execute"));
executorService.submit(() -> exeTask("execute"));
Thread.sleep(5000);
System.out.println("再次執行任務=======================");
executorService.submit(() -> exeTask("execute"));
executorService.submit(() -> exeTask("execute"));
executorService.submit(() -> exeTask("execute"));
executorService.submit(() -> exeTask("execute"));
executorService.submit(() -> exeTask("execute"));
}
public static ExecutorService buildThreadPoolExecutor() {
return new ThreadPoolExecutor(5, 10, 30, TimeUnit.SECONDS,
new LinkedBlockingQueue<>(1000), new ThreadFactoryBuilder().setNameFormat("test-%s").build()
, new ThreadPoolExecutor.CallerRunsPolicy());
}
private static void exeTask(String name) {
String printStr = "[thread-name:" + Thread.currentThread().getName() + ",執行方式:" + name + "]";
if ("execute-exception".equals(name)) {
throw new RuntimeException(printStr + ", 我拋異常了");
} else {
System.out.println(printStr);
}
}
}
2.2.2 執行結果如下:
2.2.3 結論:
submit 提交到線程池的方式,如果執行中拋出異常,並且沒有catch,不會拋出異常,不會創建新的線程。
三、源碼解析
3.1 java.util.concurrent.AbstractExecutorService#submit(java.lang.Runnable)
3.2 查看execute方法的執行邏輯java.util.concurrent.ThreadPoolExecutor#runWorker
3.3 java.util.concurrent.ThreadPoolExecutor#processWorkerExit
可以發現,如果拋出異常,會移除拋出異常的線程,創建新的線程。
3.4 爲什麼submit方法,沒有創建新的線程,而是繼續複用原線程?
還記得,我們在3.1的時候,發現submit也是調用了execute方法,但是在調用之前,包裝了一層 RunnableFuture,那一定是在RunnableFuture的實現 FutureTask中有特殊處理了,我們查看源碼可以發現。
但是,我們通過java.util.concurrent.FutureTask#get(),就可以獲取對應的異常信息。
四、總結
當一個線程池裏面的線程異常後:
以上倆種執行方式,都不會影響線程池裏面其他線程的正常執行。