Java-技术专题-多线程之线程池

{"type":"doc","content":[{"type":"heading","attrs":{"align":null,"level":3},"content":[{"type":"text","text":"一、线程池的构造"}]},{"type":"paragraph","attrs":{"indent":1,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"使用线程池离不开ThreadPoolExecutor类，该类实现了ExecutorService接口，其构造方法如下："}]},{"type":"codeblock","attrs":{"lang":null},"content":[{"type":"text","text":"public ThreadPoolExecutor(int corePoolSize,\n\tint maximumPoolSize,\n\tlong keepAliveTime,\n\tTimeUnit unit,\n\tBlockingQueue workQueue,\n\tThreadFactory threadFactory,\n\tRejectedExecutionHandler handler);1"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"参数说明如下："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#F5222D","name":"red"}},{"type":"strong"}],"text":"corePoolSize：核心池大小"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#F5222D","name":"red"}},{"type":"strong"}],"text":"maximumPoolSize：线程池大小（maximumPoolSize >= corePoolSize）"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#F5222D","name":"red"}},{"type":"strong"}],"text":"keepAliveTime：没有任务时线程的存活时间，默认情况下只有线程数目大于corePoolSize时，此参数才起作用，若线程数目等于corePoolSize，则这些线程会一直存活。但若调用allowCoreThreadTimeOut(boolean)方法，则线程数目不大于corePoolSize时，此参数也起作用，直到线程数目为0"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#F5222D","name":"red"}},{"type":"strong"}],"text":"unit：keepAliveTime的时间单位，有以下七种取值："}]},{"type":"blockquote","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"TimeUnit.DAYS;//天"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"TimeUnit.HOURS;//小时"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"TimeUnit.MINUTES;//分钟"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"TimeUnit.SECONDS;//秒"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"TimeUnit.MILLISECONDS;//毫秒"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"TimeUnit.MICROSECONDS;//微秒"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"TimeUnit.NANOSECONDS;//纳秒"}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#F5222D","name":"red"}},{"type":"strong"}],"text":"workQueue：指定构成缓冲区的阻塞队列，即指定了线程池的排队策略，常用的有以下三种："}]},{"type":"blockquote","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#F5222D","name":"red"}},{"type":"strong"}],"text":"ArrayBlockingQueue：基于数组的先进先出队列，此队列创建时必须指定大小"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#F5222D","name":"red"}},{"type":"strong"}],"text":"LinkedBlockingQueue：基于链表的先进先出队列，如果创建时没有指定此队列大小，则默认为Integer.MAX_VALUE"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#F5222D","name":"red"}},{"type":"strong"}],"text":"synchronousQueue：这个队列不会保存提交的任务，而是将直接新建一个线程来执行新来的任务"}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#F5222D","name":"red"}},{"type":"strong"}],"text":"threadFactory（可选）：线程工厂，用来创建线程，可自定义"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#F5222D","name":"red"}},{"type":"strong"}],"text":"handler（可选）：拒绝策略，有以下四种策略可选："}]},{"type":"blockquote","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#F5222D","name":"red"}},{"type":"strong"}],"text":"ThreadPoolExecutor.AbortPolicy:丢弃任务并抛出RejectedExecutionException异常。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#F5222D","name":"red"}},{"type":"strong"}],"text":"ThreadPoolExecutor.DiscardPolicy：丢弃任务，不抛出异常。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#F5222D","name":"red"}},{"type":"strong"}],"text":"ThreadPoolExecutor.DiscardOldestPolicy：丢弃队列最前面的任务，然后重新尝试执行任务"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#F5222D","name":"red"}},{"type":"strong"}],"text":"ThreadPoolExecutor.CallerRunsPolicy：由调用线程处理该任务"}]}]},{"type":"heading","attrs":{"align":null,"level":3},"content":[{"type":"text","text":"二、线程池的运行过程"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":" 如果当前线程池中的线程数目小于corePoolSize，则每来一个任务，就会创建一个线程去执行这个任务如果当前线程池中的线程数目>=corePoolSize，则每来一个任务，会尝试将其添加到任务缓存队列当中，若添加成功，则该任务会等待空闲线程将其取出去执行；若添加失败（一般来说是任务缓存队列已满），则会尝试创建新的线程去执行这个任务"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":" 如果当前线程池中的线程数目达到maximumPoolSize，则会采取任务拒绝策略进行处理"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"如果线程池中的线程数量大于"},{"type":"text","marks":[{"type":"strong"}],"text":"corePoolSize"},{"type":"text","text":"时，如果某线程空闲时间超过keepAliveTime，线程将被终止，直至线程池中的线程数目不大于corePoolSize；"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":" 如果允许为核心池中的线程设置存活时间（调用"},{"type":"codeinline","content":[{"type":"text","text":"allowCoreThreadTimeOut(boolean)"}]},{"type":"text","text":"方法），那么核心池中的线程空闲时间超过keepAliveTime，线程也会被终止"}]},{"type":"heading","attrs":{"align":null,"level":3},"content":[{"type":"text","text":"三、线程的初始化"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":" 默认情况下，线程池构造完成后是没有线程的，需要等任务提交时才会创建线程，如果需要在线程池构造完成时就创建线程，可以调用以下两个方法："}]},{"type":"paragraph","attrs":{"indent":1,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#F5222D","name":"red"}},{"type":"strong"}],"text":"prestartCoreThread()：初始化一个核心线程；"}]},{"type":"paragraph","attrs":{"indent":1,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#F5222D","name":"red"}},{"type":"strong"}],"text":"prestartAllCoreThreads()：初始化所有核心线程"}]},{"type":"heading","attrs":{"align":null,"level":3},"content":[{"type":"text","text":"四、线程池的关闭"}]},{"type":"paragraph","attrs":{"indent":1,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#F5222D","name":"red"}},{"type":"strong"}],"text":"shutdown()：不会立即关闭线程池，而是不再接受新的任务，等当前所有任务处理完之后关闭线程池"}]},{"type":"paragraph","attrs":{"indent":1,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#F5222D","name":"red"}},{"type":"strong"}],"text":"shutdownNow()：立即关闭线程池，打断正在执行的任务，清空缓冲队列，返回尚未执行的任务"}]},{"type":"heading","attrs":{"align":null,"level":3},"content":[{"type":"text","text":"五、任务提交"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"任务提交有两种方法，execute()和submit()"}]},{"type":"paragraph","attrs":{"indent":1,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#F5222D","name":"red"}},{"type":"strong"}],"text":"void execute(Runnable task)，无返回值"}]},{"type":"paragraph","attrs":{"indent":1,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#F5222D","name":"red"}},{"type":"strong"}],"text":"Futuresubmit(Runnable task, T result) /Futuresubmit(Callable task)，有返回值"}]},{"type":"heading","attrs":{"align":null,"level":3},"content":[{"type":"text","text":"六、可选线程池模型（Executors类的静态工厂方法）"}]},{"type":"blockquote","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#F5222D","name":"red"}},{"type":"strong"}],"text":"newCachedThreadPool()："},{"type":"codeinline","content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#F5222D","name":"red"}},{"type":"strong"}],"text":"ThreadPoolExecutor(0,Integer.MAX_VALUE,60L, TimeUnit.SECONDS,new SynchronousQueue())"}],"marks":[{"type":"color","attrs":{"color":"#F5222D","name":"red"}},{"type":"strong"}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#F5222D","name":"red"}},{"type":"strong"}],"text":"newFixedThreadPool(int nThreads)："},{"type":"codeinline","content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#F5222D","name":"red"}},{"type":"strong"}],"text":"ThreadPoolExecutor(nThreads,nThreads,0L, TimeUnit.MILLISECONDS,new LinkedBlockingQueue())"}],"marks":[{"type":"color","attrs":{"color":"#F5222D","name":"red"}},{"type":"strong"}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#F5222D","name":"red"}},{"type":"strong"}],"text":"newSingleThreadExecutor："},{"type":"codeinline","content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#F5222D","name":"red"}},{"type":"strong"}],"text":"ThreadPoolExecutor(1,1,0L,TimeUnit.MILLISECONDS,new LinkedBlockingQueue())"}],"marks":[{"type":"color","attrs":{"color":"#F5222D","name":"red"}},{"type":"strong"}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#F5222D","name":"red"}},{"type":"strong"}],"text":"newScheduledThreadPool(int nThreads)："},{"type":"codeinline","content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#F5222D","name":"red"}},{"type":"strong"}],"text":"ScheduledThreadPoolExecutor(nThreads,Integer.MAX_VALUE,0L,TimeUnit.NANOSECONDS,new DelayedWorkQueue())"}],"marks":[{"type":"color","attrs":{"color":"#F5222D","name":"red"}},{"type":"strong"}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#F5222D","name":"red"}},{"type":"strong"}],"text":"newSingleScheduledThreadPool()："},{"type":"codeinline","content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#F5222D","name":"red"}},{"type":"strong"}],"text":"newScheduledThreadPool(1)"}],"marks":[{"type":"color","attrs":{"color":"#F5222D","name":"red"}},{"type":"strong"}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#F5222D","name":"red"}},{"type":"strong"}],"text":"调用实例："},{"type":"codeinline","content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#F5222D","name":"red"}},{"type":"strong"}],"text":"ExecutorService pool = Executors.newCachedThreadPool();"}],"marks":[{"type":"color","attrs":{"color":"#F5222D","name":"red"}},{"type":"strong"}]}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"构造线程池时优先选用线程池模型，如果这些模型不能满足要求，再自定义ThreadPoolExecutor线程池"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}}]}