1. 提纲
1)线程池的模块结构
2)示例&原理解析
2. 问题
1)线程池包含哪些东西
2)线程池的运作原理
3)调度线程池的运作原理
4)线程池怎么实现FixRate,FixDelay,他们之间的区别
5)任务怎么取消
3. 源码解析
3.1 线程池框架
接口简介:
java.util.concurrent.Executor:执行器,执行方法
java.util.concurrent.ExecutorService:(执行服务)包含服务的生命周期
java.util.concurrent.ScheduledExecutorService:(调度相关的服务)
辅助类:
java.util.concurrent.Executors:
核心实现类:
java.util.concurrent.ThreadPoolExecutor:(普通的线程池实现类)
java.util.concurrent.ScheduledThreadPoolExecutor:(调度的核心实现类)
java.util.concurrent.ForkJoinPool
完成服务:
java.util.concurrent.CompletionService:
java.util.concurrent.ExecutorCompletionService:
3.2 ThreadPoolExecutor源码剖析
1)构造器
核心数量,任务队列容器,存活时间,线程工厂,处理器
ThreadPoolExecutor.execute()方法源码
public void execute(Runnable command) { if (command == null) throw new NullPointerException(); /* * Proceed in 3 steps: * * 1. If fewer than corePoolSize threads are running, try to * start a new thread with the given command as its first * task. The call to addWorker atomically checks runState and * workerCount, and so prevents false alarms that would add * threads when it shouldn't, by returning false. * * 2. If a task can be successfully queued, then we still need * to double-check whether we should have added a thread * (because existing ones died since last checking) or that * the pool shut down since entry into this method. So we * recheck state and if necessary roll back the enqueuing if * stopped, or start a new thread if there are none. * * 3. If we cannot queue task, then we try to add a new * thread. If it fails, we know we are shut down or saturated * and so reject the task. */ int c = ctl.get(); if (workerCountOf(c) < corePoolSize) { if (addWorker(command, true)) return; c = ctl.get(); } if (isRunning(c) && workQueue.offer(command)) { int recheck = ctl.get(); if (! isRunning(recheck) && remove(command)) reject(command); else if (workerCountOf(recheck) == 0) addWorker(null, false); } else if (!addWorker(command, false)) reject(command); }
ThreadPoolExecutor.runWorker()方法源码
final void runWorker(Worker w) { Thread wt = Thread.currentThread(); Runnable task = w.firstTask; w.firstTask = null; w.unlock(); // allow interrupts boolean completedAbruptly = true; try { while (task != null || (task = getTask()) != null) { w.lock(); // If pool is stopping, ensure thread is interrupted; // if not, ensure thread is not interrupted. This // requires a recheck in second case to deal with // shutdownNow race while clearing interrupt if ((runStateAtLeast(ctl.get(), STOP) || (Thread.interrupted() && runStateAtLeast(ctl.get(), STOP))) && !wt.isInterrupted()) wt.interrupt(); try { beforeExecute(wt, task); Throwable thrown = null; try { task.run(); } catch (RuntimeException x) { thrown = x; throw x; } catch (Error x) { thrown = x; throw x; } catch (Throwable x) { thrown = x; throw new Error(x); } finally { afterExecute(task, thrown); } } finally { task = null; w.completedTasks++; w.unlock(); } } completedAbruptly = false; } finally { processWorkerExit(w, completedAbruptly); } }
3.3 ScheduledThreadPoolExecutor
1)
2)FixRate和FixDelay的区别
/** * Sets the next time to run for a periodic task. */ private void setNextRunTime() { long p = period; if (p > 0) time += p; else time = triggerTime(-p); }
FixRate严格按照设定的时间
FixDelay按照上一个线程执行完成的时间间隔
FixRate: 21:40,21:41,21:42
FixDelay:21:40,21:43
void reExecutePeriodic(RunnableScheduledFuture<?> task) { if (canRunInCurrentRunState(true)) {
//此处没有捕获异常,如果单个任务发生异常,会导致后续任务无法继续执行 super.getQueue().add(task); if (!canRunInCurrentRunState(true) && remove(task)) task.cancel(false); else ensurePrestart(); } }