Through the previous three blog posts on the implementation of Spring Boot asynchronous tasks, we have learned use @Async to create asynchronous tasks and to configure thread pools and for asynchronous tasks. Use multiple thread pools to isolate different asynchronous tasks Today’s article, we continue to improve and optimize the above knowledge!
If you have read the above articles and have mastered them, let's think about the following questions together:
Assume that the thread pool is configured as the number of core threads 2, the maximum number of threads 2, and the buffer queue length 2. At this point, five asynchronous tasks start at the same time, what will happen?
Scene reproduction
Let's first implement the above assumption with code:
first step : Create a Spring Boot application, write the thread pool configuration according to the above assumptions.
@EnableAsync
@SpringBootApplication
public class Chapter78Application {
public static void main(String[] args) {
SpringApplication.run(Chapter78Application.class, args);
}
@EnableAsync
@Configuration
class TaskPoolConfig {
@Bean
public Executor taskExecutor1() {
ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();
executor.setCorePoolSize(2);
executor.setMaxPoolSize(2);
executor.setQueueCapacity(2);
executor.setKeepAliveSeconds(60);
executor.setThreadNamePrefix("executor-1-");
return executor;
}
}
} second step : Use @Async annotation to achieve a part of the task
@Slf4j
@Component
public class AsyncTasks {
public static Random random = new Random();
@Async("taskExecutor1")
public CompletableFuture<String> doTaskOne(String taskNo) throws Exception {
log.info("开始任务：{}", taskNo);
long start = System.currentTimeMillis();
Thread.sleep(random.nextInt(10000));
long end = System.currentTimeMillis();
log.info("完成任务：{}，耗时：{} 毫秒", taskNo, end - start);
return CompletableFuture.completedFuture("任务完成");
}
}third step : Write test cases
@Slf4j
@SpringBootTest
public class Chapter78ApplicationTests {
@Autowired
private AsyncTasks asyncTasks;
@Test
public void test2() throws Exception {
// 线程池配置：core-2,max-2,queue=2，同时有5个任务，出现下面异常：
// org.springframework.core.task.TaskRejectedException: Executor [java.util.concurrent.ThreadPoolExecutor@59901c4d[Running, pool size = 2,
// active threads = 0, queued tasks = 2, completed tasks = 4]] did not accept task: java.util.concurrent.CompletableFuture$AsyncSupply@408e96d9
long start = System.currentTimeMillis();
// 线程池1
CompletableFuture<String> task1 = asyncTasks.doTaskOne("1");
CompletableFuture<String> task2 = asyncTasks.doTaskOne("2");
CompletableFuture<String> task3 = asyncTasks.doTaskOne("3");
CompletableFuture<String> task4 = asyncTasks.doTaskOne("4");
CompletableFuture<String> task5 = asyncTasks.doTaskOne("5");
// 一起执行
CompletableFuture.allOf(task1, task2, task3, task4, task5).join();
long end = System.currentTimeMillis();
log.info("任务全部完成，总耗时：" + (end - start) + "毫秒");
}
}Execute it, you can log information similar to the following:
2021-09-22 17:33:08.159 INFO 21119 --- [ executor-1-2] com.didispace.chapter78.AsyncTasks : 开始任务：2
2021-09-22 17:33:08.159 INFO 21119 --- [ executor-1-1] com.didispace.chapter78.AsyncTasks : 开始任务：1
org.springframework.core.task.TaskRejectedException: Executor [java.util.concurrent.ThreadPoolExecutor@3e1a3801[Running, pool size = 2, active threads = 2, queued tasks = 2, completed tasks = 0]] did not accept task: java.util.concurrent.CompletableFuture$AsyncSupply@64968732
at org.springframework.scheduling.concurrent.ThreadPoolTaskExecutor.execute(ThreadPoolTaskExecutor.java:324)
at java.util.concurrent.CompletableFuture.asyncSupplyStage(CompletableFuture.java:1604)
at java.util.concurrent.CompletableFuture.supplyAsync(CompletableFuture.java:1830)
at org.springframework.aop.interceptor.AsyncExecutionAspectSupport.doSubmit(AsyncExecutionAspectSupport.java:274)
at org.springframework.aop.interceptor.AsyncExecutionInterceptor.invoke(AsyncExecutionInterceptor.java:129)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186)
at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.proceed(CglibAopProxy.java:750)
at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:692)
at com.didispace.chapter78.AsyncTasks$$EnhancerBySpringCGLIB$$c7e8d57b.doTaskOne(<generated>)
at com.didispace.chapter78.Chapter78ApplicationTests.test2(Chapter78ApplicationTests.java:51)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.junit.platform.commons.util.ReflectionUtils.invokeMethod(ReflectionUtils.java:688)
at org.junit.jupiter.engine.execution.MethodInvocation.proceed(MethodInvocation.java:60)
at org.junit.jupiter.engine.execution.InvocationInterceptorChain$ValidatingInvocation.proceed(InvocationInterceptorChain.java:131)
at org.junit.jupiter.engine.extension.TimeoutExtension.intercept(TimeoutExtension.java:149)
at org.junit.jupiter.engine.extension.TimeoutExtension.interceptTestableMethod(TimeoutExtension.java:140)
at org.junit.jupiter.engine.extension.TimeoutExtension.interceptTestMethod(TimeoutExtension.java:84)
at org.junit.jupiter.engine.execution.ExecutableInvoker$ReflectiveInterceptorCall.lambda$ofVoidMethod$0(ExecutableInvoker.java:115)
at org.junit.jupiter.engine.execution.ExecutableInvoker.lambda$invoke$0(ExecutableInvoker.java:105)
at org.junit.jupiter.engine.execution.InvocationInterceptorChain$InterceptedInvocation.proceed(InvocationInterceptorChain.java:106)
at org.junit.jupiter.engine.execution.InvocationInterceptorChain.proceed(InvocationInterceptorChain.java:64)
at org.junit.jupiter.engine.execution.InvocationInterceptorChain.chainAndInvoke(InvocationInterceptorChain.java:45)
at org.junit.jupiter.engine.execution.InvocationInterceptorChain.invoke(InvocationInterceptorChain.java:37)
at org.junit.jupiter.engine.execution.ExecutableInvoker.invoke(ExecutableInvoker.java:104)
at org.junit.jupiter.engine.execution.ExecutableInvoker.invoke(ExecutableInvoker.java:98)
at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.lambda$invokeTestMethod$6(TestMethodTestDescriptor.java:210)
at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.invokeTestMethod(TestMethodTestDescriptor.java:206)
at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.execute(TestMethodTestDescriptor.java:131)
at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.execute(TestMethodTestDescriptor.java:65)
at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$5(NodeTestTask.java:139)
at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$7(NodeTestTask.java:129)
at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:137)
at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:127)
at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:126)
at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:84)
at java.util.ArrayList.forEach(ArrayList.java:1255)
at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.invokeAll(SameThreadHierarchicalTestExecutorService.java:38)
at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$5(NodeTestTask.java:143)
at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$7(NodeTestTask.java:129)
at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:137)
at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:127)
at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:126)
at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:84)
at java.util.ArrayList.forEach(ArrayList.java:1255)
at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.invokeAll(SameThreadHierarchicalTestExecutorService.java:38)
at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$5(NodeTestTask.java:143)
at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$7(NodeTestTask.java:129)
at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:137)
at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:127)
at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:126)
at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:84)
at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.submit(SameThreadHierarchicalTestExecutorService.java:32)
at org.junit.platform.engine.support.hierarchical.HierarchicalTestExecutor.execute(HierarchicalTestExecutor.java:57)
at org.junit.platform.engine.support.hierarchical.HierarchicalTestEngine.execute(HierarchicalTestEngine.java:51)
at org.junit.platform.launcher.core.EngineExecutionOrchestrator.execute(EngineExecutionOrchestrator.java:108)
at org.junit.platform.launcher.core.EngineExecutionOrchestrator.execute(EngineExecutionOrchestrator.java:88)
at org.junit.platform.launcher.core.EngineExecutionOrchestrator.lambda$execute$0(EngineExecutionOrchestrator.java:54)
at org.junit.platform.launcher.core.EngineExecutionOrchestrator.withInterceptedStreams(EngineExecutionOrchestrator.java:67)
at org.junit.platform.launcher.core.EngineExecutionOrchestrator.execute(EngineExecutionOrchestrator.java:52)
at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:96)
at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:75)
at com.intellij.junit5.JUnit5IdeaTestRunner.startRunnerWithArgs(JUnit5IdeaTestRunner.java:71)
at com.intellij.rt.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:33)
at com.intellij.rt.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:235)
at com.intellij.rt.junit.JUnitStarter.main(JUnitStarter.java:54)
Caused by: java.util.concurrent.RejectedExecutionException: Task java.util.concurrent.CompletableFuture$AsyncSupply@64968732 rejected from java.util.concurrent.ThreadPoolExecutor@3e1a3801[Running, pool size = 2, active threads = 2, queued tasks = 2, completed tasks = 0]
at java.util.concurrent.ThreadPoolExecutor$AbortPolicy.rejectedExecution(ThreadPoolExecutor.java:2063)
at java.util.concurrent.ThreadPoolExecutor.reject(ThreadPoolExecutor.java:830)
at java.util.concurrent.ThreadPoolExecutor.execute(ThreadPoolExecutor.java:1379)
at org.springframework.scheduling.concurrent.ThreadPoolTaskExecutor.execute(ThreadPoolTaskExecutor.java:321)
... 74 moreFrom the exception information org.springframework.core.task.TaskRejectedException: Executor [java.util.concurrent.ThreadPoolExecutor@3e1a3801[Running, pool size = 2, active threads = 2, queued tasks = 2, completed tasks = 0]] did not accept task: , it is clear that the fifth task was rejected because it exceeded the execution thread + buffer queue length.
All, by default, the rejection policy of the thread pool is: when the thread pool queue is full, the task will be discarded and an exception will be thrown.
Configure deny policy
Although the thread pool has a default rejection strategy, in the actual development process, in some business scenarios, the direct rejection strategy is often not applicable. Sometimes we may choose to abandon tasks that have not been completed at the earliest, or may choose to abandon A strategy that is closer to business needs, such as tasks that have been started but not completed. Therefore, it is a very common requirement to configure other rejection strategies or custom rejection strategies for the thread pool, so how can this be achieved?
Let's talk about today's topic specifically, how to configure the rejection strategy for the thread pool, and how to customize the rejection strategy.
Look at the last line of the following code, the setRejectedExecutionHandler method is to set the rejection policy for the thread pool:
ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();
//...其他线程池配置
executor.setRejectedExecutionHandler(new ThreadPoolExecutor.AbortPolicy());In ThreadPoolExecutor , 4 thread strategies are provided for developers to use directly. You only need to set it as follows:
// AbortPolicy策略
executor.setRejectedExecutionHandler(new ThreadPoolExecutor.AbortPolicy());
// DiscardPolicy策略
executor.setRejectedExecutionHandler(new ThreadPoolExecutor.DiscardPolicy());
// DiscardOldestPolicy策略
executor.setRejectedExecutionHandler(new ThreadPoolExecutor.DiscardOldestPolicy());
// CallerRunsPolicy策略
executor.setRejectedExecutionHandler(new ThreadPoolExecutor.CallerRunsPolicy());The corresponding meanings of these four strategies are:
- AbortPolicy strategy: The default strategy, if the thread pool queue is full, discard the task and throw a RejectedExecutionException exception.
- DiscardPolicy strategy: If the thread pool queue is full, the task will be directly discarded without any exception.
- DiscardOldestPolicy strategy: If the queue is full, the earliest task that entered the queue will be deleted to make room, and then try to join the queue.
- CallerRunsPolicy strategy: If adding to the thread pool fails, the main thread will perform the task by itself, and will not wait for the threads in the thread pool to execute.
And if you want to customize a rejection strategy, you can write it like this:
executor.setRejectedExecutionHandler(new RejectedExecutionHandler() {
@Override
public void rejectedExecution(Runnable r, ThreadPoolExecutor executor) {
// 拒绝策略的逻辑
}
});Of course, if you like to use Lamba expressions, you can also write like this:
executor.setRejectedExecutionHandler((r, executor1) -> {
// 拒绝策略的逻辑
});Well, that's all for today's study!
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Code example
The complete project of this article can be viewed in chapter7-8 project 2.x directory in the following warehouse:
- Github：https://github.com/dyc87112/SpringBoot-Learning/
- Gitee：https://gitee.com/didispace/SpringBoot-Learning/
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