# \[Thread] ThreadPoolExecutor 정리 ## Java의 ThreadPoolExecutor Thread Pool은 애플리케이션의 특징 및 JVM을 구동하는 하드웨어 사양에 따라 세밀하게 조정해야 한다. Java 1.5 이 후 ExecutorService 구현체인 `ThreadPoolExecutor`를 통해 Thread Pool을 직접 설정하여 사용할 수 있다. ```java package java.util.concurrent; public ThreadPoolExecutor(int corePoolSize, int maximumPoolSize, long keepAliveTime, TimeUnit unit, BlockingQueue workQueue, ThreadFactory threadFactory, RejectedExecutionHandler handler) { // ... init code } ```
파라미터설명
corePoolSizeThread Pool에 계속해서 유지할 Thread 수
maximumPoolSizeThread Pool에 최대한으로 가질 수 있는 Thread 수
* workQueue가 가득 찼을 때 Thread 개수를 늘린다.
keepAliveTime기본으로 유지하고 있는 Thread 외에 증가한 Thread를 유지할 시간 설정
unitkeepAliveTime에서 사용할 TimeUnit 타입
workQueueTask가 corePoolSize를 초과할 때 보관할 BlockingQueue 정의
threadFactory(not required) Thread Pool에서 Thread를 생성할 때 사용할 threadFactory 정의
handler(not required) Thread Pool이 가득차서 더 이상 작업을 수용할 수 없을 때 사용되는 핸들러
{% hint style="info" %} Task 요청이 들어오면 아래의 순서로 ThreadPoolExecutor가 작동한다. *corePoolSize 증가 → workQueue 증가 → maximumPoolSize 증가* {% endhint %} ### 테스트 코드 작성 maximumPoolSize, queueSize 내에서 실행 가능한 크기로 사용. ```java @Test void threadPoolTaskExecutorTest() { int corePoolSize = 5; int maximumPoolSize = 10; int queueSize = 5; ThreadPoolExecutor executor = new ThreadPoolExecutor( corePoolSize, maximumPoolSize, 10, TimeUnit.SECONDS, new LinkedBlockingQueue<>(queueSize)); IntStream.range(0, 15).forEach(i -> { executor.execute(() -> { // 무거운 작업 }); System.out.println(executor); }); try { executor.shutdown(); executor.awaitTermination(Long.MAX_VALUE, TimeUnit.SECOUNDS); } catch (InterruptedException e) { // ... } } ``` ``` [Running, pool size = 1, active threads = 1, queued tasks = 0, completed tasks = 0] [Running, pool size = 2, active threads = 2, queued tasks = 0, completed tasks = 0] [Running, pool size = 3, active threads = 3, queued tasks = 0, completed tasks = 0] [Running, pool size = 4, active threads = 4, queued tasks = 0, completed tasks = 0] [Running, pool size = 5, active threads = 5, queued tasks = 0, completed tasks = 0] [Running, pool size = 5, active threads = 5, queued tasks = 1, completed tasks = 0] [Running, pool size = 5, active threads = 5, queued tasks = 2, completed tasks = 0] [Running, pool size = 5, active threads = 5, queued tasks = 3, completed tasks = 0] [Running, pool size = 5, active threads = 5, queued tasks = 4, completed tasks = 0] [Running, pool size = 5, active threads = 5, queued tasks = 5, completed tasks = 0] [Running, pool size = 6, active threads = 6, queued tasks = 5, completed tasks = 0] [Running, pool size = 7, active threads = 7, queued tasks = 5, completed tasks = 0] [Running, pool size = 8, active threads = 8, queued tasks = 5, completed tasks = 0] [Running, pool size = 9, active threads = 9, queued tasks = 5, completed tasks = 0] [Running, pool size = 10, active threads = 10, queued tasks = 5, completed tasks = 0] ``` 사용 가능한 Thread가 있을 때는 Thread를 가져다 사용하므로 corePoolSize 만큼 active threads를 사용한다. 그 이후 corePoolSize 사용량이 다 찬 경우 queued tasks가 채워지는 것을 확인할 수 있다. queued tasks의 capacity 만큼 Queue가 가득 찬 경우 maximumPoolSize 만큼 active threads가 늘어난다. #### maximumPoolSize보다 더 많은 작업을 돌리는 경우 ```java // ... IntStream.range(0, 20).forEach(i -> { // ... }); // ... ``` ``` java.util.concurrent.RejectedExecutionException: Task com.example.funch.DemoApplicationTests$$Lambda/0x0000020ba4588230@27896d3b rejected from java.util.concurrent.ThreadPoolExecutor@5fb07347 [Running, pool size = 10, active threads = 10, queued tasks = 5, completed tasks = 0] ``` 위와 같이 `RejectedExecutionException` 예외가 발생한다. 예외를 처리하기 위해선 ThreadPoolTaskExecutor를 생성할 때 `RejectedExecutionHandler` 로 제어할 수 있다. ## Spring의 ThreadPoolTaskExecutor ```java package org.springframework.scheduling.concurrent; public class ThreadPoolTaskExecutor extends ExecutorConfigurationSupport implements AsyncListenableTaskExecutor, SchedulingTaskExecutor { private int corePoolSize = 1; private int maxPoolSize = Integer.MAX_VALUE; private int keepAliveSeconds = 60; private int queueCapacity = Integer.MAX_VALUE; // ... @Override protected ExecutorService initializeExecutor(ThreadFactory threadFactory, RejectedExecutionHandler rejectedExecutionHandler) { BlockingQueue queue = this.createQueue(this.queueCapacity); // ... ThreadPoolExecutor executor = new ThreadPoolExecutor(this.corePoolSize, this.maxPoolSize, (long)this.keepAliveSeconds, TimeUnit.SECONDS, queue, threadFactory, rejectedExecutionHandler) { // ... } // ... return executor; } // ... } ``` ThreadPoolTaskExecutor에서 초기화할 때 내부적으로 `ThreadPoolExecutor`를 생성하여 사용하고 있다. --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://funch.gitbook.io/record/dev/spring/thread-threadpoolexecutor.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.