ThreadPoolTaskExecutor是一個spring的線程池技術,它內部屬性使用的是jdk中的java.util.concurrent.ThreadPoolExecutor進行實現,等同於ThreadPoolExecutor創建的線程池。
ThreadPoolTaskExecutor的參數:int corePoolSize:線程池維護線程的最小數量.
int maximumPoolSize:線程池維護線程的最大數量.
long keepAliveTime:空閒線程的存活時間.
TimeUnit unit: 時間單位,現有納秒,微秒,毫秒,秒枚舉值.
BlockingQueue<Runnable> workQueue:持有等待執行的任務隊列.
RejectedExecutionHandler handler: 用來拒絕一個任務的執行,有兩種情況會發生這種情況。
一是在execute方法中若addIfUnderMaximumPoolSize(command)爲false,即線程池已經飽和;
二是在execute方法中, 發現runState!=RUNNING || poolSize == 0,即已經shutdown,就調用ensureQueuedTaskHandled(Runnable command),在該方法中有可能調用reject。
Spring Boot自定義線程池
package com.boot.admin.thread;
import java.util.concurrent.Executor;
import java.util.concurrent.ThreadPoolExecutor;
import org.springframework.aop.interceptor.AsyncUncaughtExceptionHandler;
import org.springframework.context.annotation.Configuration;
import org.springframework.scheduling.annotation.AsyncConfigurer;
import org.springframework.scheduling.annotation.EnableAsync;
import org.springframework.scheduling.concurrent.ThreadPoolTaskExecutor;
@Configuration
@EnableAsync //開啓異步任務支持
public class ThreadPoolConfig implements AsyncConfigurer {
private static final int CORE_POLL_SIZE = 150;
private static final int MAX_POLL_SIZE = 200;
private static final int QUEUE_CAPACITY = 1000000;
private static final int KEEP_ALIVE_SECONDS = 60;
/**
* 實現AsyncConfigurer接口並重寫getAsyncExecutor方法,
* 創建線程池ThreadPoolTaskExecutor(Spring自帶的線程池與Java使用的還是有些區分),並返回
*/
@Override
public Executor getAsyncExecutor() {
ThreadPoolTaskExecutor taskExecutor = new ThreadPoolTaskExecutor();
taskExecutor.setCorePoolSize(CORE_POLL_SIZE);//核心線程數
taskExecutor.setMaxPoolSize(MAX_POLL_SIZE);//最大線程數
taskExecutor.setQueueCapacity(QUEUE_CAPACITY);//隊列最大長度
taskExecutor.setKeepAliveSeconds(KEEP_ALIVE_SECONDS);//線程池維護線程所允許的空閒時間
taskExecutor.setRejectedExecutionHandler(new ThreadPoolExecutor.CallerRunsPolicy());//線程池對拒絕任務(無線程可用)的處理策略
taskExecutor.initialize();
return taskExecutor;
}
@Override
public AsyncUncaughtExceptionHandler getAsyncUncaughtExceptionHandler() {
// TODO Auto-generated method stub
return null;
}
}
Reject策略預定義有四種: (1)ThreadPoolExecutor.AbortPolicy策略,是默認的策略,處理程序遭到拒絕將拋出運行時 RejectedExecutionException。
(2)ThreadPoolExecutor.CallerRunsPolicy策略 ,調用者的線程會執行該任務,如果執行器已關閉,則丟棄.
(3)ThreadPoolExecutor.DiscardPolicy策略,不能執行的任務將被丟棄.
(4)ThreadPoolExecutor.DiscardOldestPolicy策略,如果執行程序尚未關閉,則位於工作隊列頭部的任務將被刪除,然後重試執行程序(如果再次失敗,則重複此過程).