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springboot中@Async默认线程池导致OOM问题

程序员文章站 2022-05-06 23:05:47
前言:1.最近项目上在测试人员压测过程中发现了oom问题,项目使用springboot搭建项目工程,通过查看日志中包含信息:unable to create new native thread内存溢出...

前言:

1.最近项目上在测试人员压测过程中发现了oom问题,项目使用springboot搭建项目工程,通过查看日志中包含信息:unable to create new native thread

内存溢出的三种类型:
1.第一种outofmemoryerror: permgen space,发生这种问题的原意是程序中使用了大量的jar或class
2.第二种outofmemoryerror: java heap space,发生这种问题的原因是java虚拟机创建的对象太多
3.第三种outofmemoryerror:unable to create new native thread,创建线程数量太多,占用内存过大

初步分析:

1.初步怀疑是线程创建太多导致,使用jstack 线程号 > /tmp/oom.log将应用的线程信息打印出来。查看oom.log,发现大量线程处于runnable状态,基本可以确认是线程创建太多了。

代码分析:

1.出问题的微服务是日志写库服务,对比日志,锁定在writelog方法上,wirtelog方法使用spring-@async注解,写库操作采用的是异步写入方式。
2.之前没有对@async注解深入研究过,只是知道可以自定义内部线程池,经查看,日志写库服务并未自定义异步配置,使用的是spring-@async默认异步配置
3.首先简单百度了下,网上提到@async默认异步配置使用的是simpleasynctaskexecutor,该线程池默认来一个任务创建一个线程,在压测情况下,会有大量写库请求进入日志写库服务,这时就会不断创建大量线程,极有可能压爆服务器内存。

借此机会也学习了下simpleasynctaskexecutor源码,总结如下:

1.simpleasynctaskexecutor提供了限流机制,通过concurrencylimit属性来控制开关,当concurrencylimit>=0时开启限流机制,默认关闭限流机制即concurrencylimit=-1,当关闭情况下,会不断创建新的线程来处理任务,核心代码如下:

public void execute(runnable task, long starttimeout) {
  assert.notnull(task, "runnable must not be null");
  runnable tasktouse = (this.taskdecorator != null ? this.taskdecorator.decorate(task) : task);
  //判断是否开启限流机制
  if (isthrottleactive() && starttimeout > timeout_immediate) {
   //执行前置操作,进行限流
   this.concurrencythrottle.beforeaccess();
   //执行完线程任务,会执行后置操作concurrencythrottle.afteraccess(),配合进行限流
   doexecute(new concurrencythrottlingrunnable(tasktouse));
  }
  else {
   doexecute(tasktouse);
  }
}

2.simpleasynctaskexecutor限流实现

首先任务进来,会循环判断当前执行线程数是否超过concurrencylimit,如果超了,则当前线程调用wait方法,释放monitor对象锁,进入等待

protected void beforeaccess() {
	if (this.concurrencylimit == no_concurrency) {
		throw new illegalstateexception(
				"currently no invocations allowed - concurrency limit set to no_concurrency");
	}
	if (this.concurrencylimit > 0) {
		boolean debug = logger.isdebugenabled();
		synchronized (this.monitor) {
			boolean interrupted = false;
			while (this.concurrencycount >= this.concurrencylimit) {
				if (interrupted) {
					throw new illegalstateexception("thread was interrupted while waiting for invocation access, " +
							"but concurrency limit still does not allow for entering");
				}
				if (debug) {
					logger.debug("concurrency count " + this.concurrencycount +
							" has reached limit " + this.concurrencylimit + " - blocking");
				}
				try {
					this.monitor.wait();
				}
				catch (interruptedexception ex) {
					// re-interrupt current thread, to allow other threads to react.
					thread.currentthread().interrupt();
					interrupted = true;
				}
			}
			if (debug) {
				logger.debug("entering throttle at concurrency count " + this.concurrencycount);
			}
			this.concurrencycount++;
		}
	}
}

2.simpleasynctaskexecutor限流实现:首先任务进来,会循环判断当前执行线程数是否超过concurrencylimit,如果超了,则当前线程调用wait方法,释放monitor对象锁,进入等待状态。

protected void beforeaccess() {
	if (this.concurrencylimit == no_concurrency) {
		throw new illegalstateexception(
				"currently no invocations allowed - concurrency limit set to no_concurrency");
	}
	if (this.concurrencylimit > 0) {
		boolean debug = logger.isdebugenabled();
		synchronized (this.monitor) {
			boolean interrupted = false;
			while (this.concurrencycount >= this.concurrencylimit) {
				if (interrupted) {
					throw new illegalstateexception("thread was interrupted while waiting for invocation access, " +
							"but concurrency limit still does not allow for entering");
				}
				if (debug) {
					logger.debug("concurrency count " + this.concurrencycount +
							" has reached limit " + this.concurrencylimit + " - blocking");
				}
				try {
					this.monitor.wait();
				}
				catch (interruptedexception ex) {
					// re-interrupt current thread, to allow other threads to react.
					thread.currentthread().interrupt();
					interrupted = true;
				}
			}
			if (debug) {
				logger.debug("entering throttle at concurrency count " + this.concurrencycount);
			}
			this.concurrencycount++;
		}
	}
}

线程任务执行完毕后,当前执行线程数会减一,会调用monitor对象的notify方法,唤醒等待状态下的线程,等待状态下的线程会竞争monitor锁,竞争到,会继续执行线程任务。

protected void afteraccess() {
	if (this.concurrencylimit >= 0) {
		synchronized (this.monitor) {
			this.concurrencycount--;
			if (logger.isdebugenabled()) {
				logger.debug("returning from throttle at concurrency count " + this.concurrencycount);
			}
			this.monitor.notify();
		}
	}
}

虽然看了源码了解了simpleasynctaskexecutor有限流机制,实践出真知,我们还是测试下:
一、测试未开启限流机制下,我们启动20个线程去调用异步方法,查看java visualvm工具如下:

springboot中@Async默认线程池导致OOM问题

二、测试开启限流机制,开启限流机制的代码如下:

@configuration
@enableasync
public class asynccommonconfig extends asyncconfigurersupport {
  @override
  public executor getasyncexecutor() {
    simpleasynctaskexecutor executor = new simpleasynctaskexecutor();
    //设置允许同时执行的线程数为10
 executor.setconcurrencylimit(10);
    return executor;
  }
}

同样,我们启动20个线程去调用异步方法,查看java visualvm工具如下:

springboot中@Async默认线程池导致OOM问题

通过上面验证可知:
1.开启限流情况下,能有效控制应用线程数
2.虽然可以有效控制线程数,但执行效率会降低,会出现主线程等待,线程竞争的情况。
3.限流机制适用于任务处理比较快的场景,对于应用处理时间比较慢的场景并不适用。==

最终解决办法:
1.自定义线程池,使用linkedblockingqueue阻塞队列来限定线程池的上限
2.定义拒绝策略,如果队列满了,则拒绝处理该任务,打印日志,代码如下:

public class asyncconfig implements asyncconfigurer{
  private logger logger = logmanager.getlogger();

  @value("${thread.pool.corepoolsize:10}")
  private int corepoolsize;

  @value("${thread.pool.maxpoolsize:20}")
  private int maxpoolsize;

  @value("${thread.pool.keepaliveseconds:4}")
  private int keepaliveseconds;

  @value("${thread.pool.queuecapacity:512}")
  private int queuecapacity;

  @override
  public executor getasyncexecutor() {
    threadpooltaskexecutor executor = new threadpooltaskexecutor();
    executor.setcorepoolsize(corepoolsize);
    executor.setmaxpoolsize(maxpoolsize);
    executor.setkeepaliveseconds(keepaliveseconds);
    executor.setqueuecapacity(queuecapacity);
    executor.setrejectedexecutionhandler((runnable r, threadpoolexecutor exe) -> {
        logger.warn("当前任务线程池队列已满.");
    });
    executor.initialize();
    return executor;
  }

  @override
  public asyncuncaughtexceptionhandler getasyncuncaughtexceptionhandler() {
    return new asyncuncaughtexceptionhandler() {
      @override
      public void handleuncaughtexception(throwable ex , method method , object... params) {
        logger.error("线程池执行任务发生未知异常.", ex);
      }
    };
  }
}

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