“`”
<p cid=""n152"" mdtype=""paragraph"" class=""md-end-block md-p md-focus"" style=""line-height: inherit; orphans: 4; margin: 0.8em 0px; white-space: pre-wrap; position: relative; color: rgb(51, 51, 51); font-family: "Open Sans", "Clear Sans", "Helvetica Neue", Helvetica, Arial, sans-serif;""><span md-inline=""plain"" class=""md-plain md-expand"">java多线程开发时，常常用到线程池技术，这篇文章是对创建java线程池时的七个参数的详细解释。</span></p>
<p cid=""n155"" mdtype=""paragraph"" class=""md-end-block md-p"" style=""line-height: inherit; orphans: 4; margin: 0.8em 0px; white-space: pre-wrap; position: relative; color: rgb(51, 51, 51); font-family: "Open Sans", "Clear Sans", "Helvetica Neue", Helvetica, Arial, sans-serif;""><span md-inline=""plain"" class=""md-plain""> </span><img src=""http://res.mianshigee.com/upload/article/20200417/e6ba8f3f-9081-4889-83ed-f26485f8bbcb.png"" style=""width: 510px;""></p>
<p cid=""n156"" mdtype=""paragraph"" class=""md-end-block md-p"" style=""line-height: inherit; orphans: 4; margin: 0.8em 0px; white-space: pre-wrap; position: relative; color: rgb(51, 51, 51); font-family: "Open Sans", "Clear Sans", "Helvetica Neue", Helvetica, Arial, sans-serif;""><span md-inline=""plain"" class=""md-plain"">从源码中可以看出，线程池的构造函数有7个参数，分别是corePoolSize、maximumPoolSize、keepAliveTime、unit、workQueue、threadFactory、handler。下面会对这7个参数一一解释。</span></p>
<p cid=""n157"" mdtype=""paragraph"" class=""md-end-block md-p"" style=""line-height: inherit; orphans: 4; margin: 0.8em 0px; white-space: pre-wrap; position: relative; color: rgb(51, 51, 51); font-family: "Open Sans", "Clear Sans", "Helvetica Neue", Helvetica, Arial, sans-serif;""><span md-inline=""strong"" class=""""><strong>一、corePoolSize 线程池核心线程大小</strong></span></p>
<p cid=""n158"" mdtype=""paragraph"" class=""md-end-block md-p"" style=""line-height: inherit; orphans: 4; margin: 0.8em 0px; white-space: pre-wrap; position: relative; color: rgb(51, 51, 51); font-family: "Open Sans", "Clear Sans", "Helvetica Neue", Helvetica, Arial, sans-serif;""><span md-inline=""plain"" class=""md-plain"">线程池中会维护一个最小的线程数量，即使这些线程处理空闲状态，他们也不会 被销毁，除非设置了allowCoreThreadTimeOut。这里的最小线程数量即是corePoolSize。</span></p>
<p cid=""n159"" mdtype=""paragraph"" class=""md-end-block md-p"" style=""line-height: inherit; orphans: 4; margin: 0.8em 0px; white-space: pre-wrap; position: relative; color: rgb(51, 51, 51); font-family: "Open Sans", "Clear Sans", "Helvetica Neue", Helvetica, Arial, sans-serif;""><span md-inline=""strong"" class=""""><strong>二、maximumPoolSize 线程池最大线程数量</strong></span></p>
<p cid=""n160"" mdtype=""paragraph"" class=""md-end-block md-p"" style=""line-height: inherit; orphans: 4; margin: 0.8em 0px; white-space: pre-wrap; position: relative; color: rgb(51, 51, 51); font-family: "Open Sans", "Clear Sans", "Helvetica Neue", Helvetica, Arial, sans-serif;""><span md-inline=""plain"" class=""md-plain"">一个任务被提交到线程池后，首先会缓存到工作队列（后面会介绍）中，如果工作队列满了，则会创建一个新线程，然后从工作队列中的取出一个任务交由新线程来处理，而将刚提交的任务放入工作队列。线程池不会无限制的去创建新线程，它会有一个最大线程数量的限制，这个数量即由maximunPoolSize来指定。</span></p>
<p cid=""n161"" mdtype=""paragraph"" class=""md-end-block md-p"" style=""line-height: inherit; orphans: 4; margin: 0.8em 0px; white-space: pre-wrap; position: relative; color: rgb(51, 51, 51); font-family: "Open Sans", "Clear Sans", "Helvetica Neue", Helvetica, Arial, sans-serif;""><span md-inline=""strong"" class=""""><strong>三、keepAliveTime 空闲线程存活时间</strong></span></p>
<p cid=""n162"" mdtype=""paragraph"" class=""md-end-block md-p"" style=""line-height: inherit; orphans: 4; margin: 0.8em 0px; white-space: pre-wrap; position: relative; color: rgb(51, 51, 51); font-family: "Open Sans", "Clear Sans", "Helvetica Neue", Helvetica, Arial, sans-serif;""><span md-inline=""plain"" class=""md-plain"">一个线程如果处于空闲状态，并且当前的线程数量大于corePoolSize，那么在指定时间后，这个空闲线程会被销毁，这里的指定时间由keepAliveTime来设定</span></p>
<p cid=""n163"" mdtype=""paragraph"" class=""md-end-block md-p"" style=""line-height: inherit; orphans: 4; margin: 0.8em 0px; white-space: pre-wrap; position: relative; color: rgb(51, 51, 51); font-family: "Open Sans", "Clear Sans", "Helvetica Neue", Helvetica, Arial, sans-serif;""><span md-inline=""strong"" class=""""><strong>四、unit 空间线程存活时间单位</strong></span></p>
<p cid=""n164"" mdtype=""paragraph"" class=""md-end-block md-p"" style=""line-height: inherit; orphans: 4; margin: 0.8em 0px; white-space: pre-wrap; position: relative; color: rgb(51, 51, 51); font-family: "Open Sans", "Clear Sans", "Helvetica Neue", Helvetica, Arial, sans-serif;""><span md-inline=""plain"" class=""md-plain"">keepAliveTime的计量单位</span></p>
<p cid=""n165"" mdtype=""paragraph"" class=""md-end-block md-p"" style=""line-height: inherit; orphans: 4; margin: 0.8em 0px; white-space: pre-wrap; position: relative; color: rgb(51, 51, 51); font-family: "Open Sans", "Clear Sans", "Helvetica Neue", Helvetica, Arial, sans-serif;""><span md-inline=""strong"" class=""""><strong>五、workQueue 工作队列</strong></span></p>
<p cid=""n166"" mdtype=""paragraph"" class=""md-end-block md-p"" style=""line-height: inherit; orphans: 4; margin: 0.8em 0px; white-space: pre-wrap; position: relative; color: rgb(51, 51, 51); font-family: "Open Sans", "Clear Sans", "Helvetica Neue", Helvetica, Arial, sans-serif;""><span md-inline=""plain"" class=""md-plain"">新任务被提交后，会先进入到此工作队列中，任务调度时再从队列中取出任务。jdk中提供了四种工作队列：</span></p>
<p cid=""n167"" mdtype=""paragraph"" class=""md-end-block md-p"" style=""line-height: inherit; orphans: 4; margin: 0.8em 0px; white-space: pre-wrap; position: relative; color: rgb(51, 51, 51); font-family: "Open Sans", "Clear Sans", "Helvetica Neue", Helvetica, Arial, sans-serif;""><span md-inline=""plain"" class=""md-plain"">①ArrayBlockingQueue</span></p>
<p cid=""n168"" mdtype=""paragraph"" class=""md-end-block md-p"" style=""line-height: inherit; orphans: 4; margin: 0.8em 0px; white-space: pre-wrap; position: relative; color: rgb(51, 51, 51); font-family: "Open Sans", "Clear Sans", "Helvetica Neue", Helvetica, Arial, sans-serif;""><span md-inline=""plain"" class=""md-plain"">基于数组的有界阻塞队列，按FIFO排序。新任务进来后，会放到该队列的队尾，有界的数组可以防止资源耗尽问题。当线程池中线程数量达到corePoolSize后，再有新任务进来，则会将任务放入该队列的队尾，等待被调度。如果队列已经是满的，则创建一个新线程，如果线程数量已经达到maxPoolSize，则会执行拒绝策略。</span></p>
<p cid=""n169"" mdtype=""paragraph"" class=""md-end-block md-p"" style=""line-height: inherit; orphans: 4; margin: 0.8em 0px; white-space: pre-wrap; position: relative; color: rgb(51, 51, 51); font-family: "Open Sans", "Clear Sans", "Helvetica Neue", Helvetica, Arial, sans-serif;""><span md-inline=""plain"" class=""md-plain"">②LinkedBlockingQuene</span></p>
<p cid=""n170"" mdtype=""paragraph"" class=""md-end-block md-p"" style=""line-height: inherit; orphans: 4; margin: 0.8em 0px; white-space: pre-wrap; position: relative; color: rgb(51, 51, 51); font-family: "Open Sans", "Clear Sans", "Helvetica Neue", Helvetica, Arial, sans-serif;""><span md-inline=""plain"" class=""md-plain"">基于链表的无界阻塞队列（其实最大容量为Interger.MAX），按照FIFO排序。由于该队列的近似无界性，当线程池中线程数量达到corePoolSize后，再有新任务进来，会一直存入该队列，而不会去创建新线程直到maxPoolSize，因此使用该工作队列时，参数maxPoolSize其实是不起作用的。</span></p>
<p cid=""n171"" mdtype=""paragraph"" class=""md-end-block md-p"" style=""line-height: inherit; orphans: 4; margin: 0.8em 0px; white-space: pre-wrap; position: relative; color: rgb(51, 51, 51); font-family: "Open Sans", "Clear Sans", "Helvetica Neue", Helvetica, Arial, sans-serif;""><span md-inline=""plain"" class=""md-plain"">③SynchronousQuene</span></p>
<p cid=""n172"" mdtype=""paragraph"" class=""md-end-block md-p"" style=""line-height: inherit; orphans: 4; margin: 0.8em 0px; white-space: pre-wrap; position: relative; color: rgb(51, 51, 51); font-family: "Open Sans", "Clear Sans", "Helvetica Neue", Helvetica, Arial, sans-serif;""><span md-inline=""plain"" class=""md-plain"">一个不缓存任务的阻塞队列，生产者放入一个任务必须等到消费者取出这个任务。也就是说新任务进来时，不会缓存，而是直接被调度执行该任务，如果没有可用线程，则创建新线程，如果线程数量达到maxPoolSize，则执行拒绝策略。</span></p>
<p cid=""n173"" mdtype=""paragraph"" class=""md-end-block md-p"" style=""line-height: inherit; orphans: 4; margin: 0.8em 0px; white-space: pre-wrap; position: relative; color: rgb(51, 51, 51); font-family: "Open Sans", "Clear Sans", "Helvetica Neue", Helvetica, Arial, sans-serif;""><span md-inline=""plain"" class=""md-plain"">④PriorityBlockingQueue</span></p>
<p cid=""n174"" mdtype=""paragraph"" class=""md-end-block md-p"" style=""line-height: inherit; orphans: 4; margin: 0.8em 0px; white-space: pre-wrap; position: relative; color: rgb(51, 51, 51); font-family: "Open Sans", "Clear Sans", "Helvetica Neue", Helvetica, Arial, sans-serif;""><span md-inline=""plain"" class=""md-plain"">具有优先级的无界阻塞队列，优先级通过参数Comparator实现。</span></p>
<p cid=""n175"" mdtype=""paragraph"" class=""md-end-block md-p"" style=""line-height: inherit; orphans: 4; margin: 0.8em 0px; white-space: pre-wrap; position: relative; color: rgb(51, 51, 51); font-family: "Open Sans", "Clear Sans", "Helvetica Neue", Helvetica, Arial, sans-serif;""><span md-inline=""strong"" class=""""><strong>六、threadFactory 线程工厂</strong></span></p>
<p cid=""n176"" mdtype=""paragraph"" class=""md-end-block md-p"" style=""line-height: inherit; orphans: 4; margin: 0.8em 0px; white-space: pre-wrap; position: relative; color: rgb(51, 51, 51); font-family: "Open Sans", "Clear Sans", "Helvetica Neue", Helvetica, Arial, sans-serif;""><span md-inline=""plain"" class=""md-plain"">创建一个新线程时使用的工厂，可以用来设定线程名、是否为daemon线程等等</span></p>
<p cid=""n177"" mdtype=""paragraph"" class=""md-end-block md-p"" style=""line-height: inherit; orphans: 4; margin: 0.8em 0px; white-space: pre-wrap; position: relative; color: rgb(51, 51, 51); font-family: "Open Sans", "Clear Sans", "Helvetica Neue", Helvetica, Arial, sans-serif;""><span md-inline=""strong"" class=""""><strong>七、handler 拒绝策略</strong></span></p>
<p cid=""n178"" mdtype=""paragraph"" class=""md-end-block md-p"" style=""line-height: inherit; orphans: 4; margin: 0.8em 0px; white-space: pre-wrap; position: relative; color: rgb(51, 51, 51); font-family: "Open Sans", "Clear Sans", "Helvetica Neue", Helvetica, Arial, sans-serif;""><span md-inline=""plain"" class=""md-plain"">当工作队列中的任务已到达最大限制，并且线程池中的线程数量也达到最大限制，这时如果有新任务提交进来，该如何处理呢。这里的拒绝策略，就是解决这个问题的，jdk中提供了4中拒绝策略：</span></p>
<p cid=""n179"" mdtype=""paragraph"" class=""md-end-block md-p"" style=""line-height: inherit; orphans: 4; margin: 0.8em 0px; white-space: pre-wrap; position: relative; color: rgb(51, 51, 51); font-family: "Open Sans", "Clear Sans", "Helvetica Neue", Helvetica, Arial, sans-serif;""><span md-inline=""plain"" class=""md-plain"">①CallerRunsPolicy</span></p>
<p cid=""n180"" mdtype=""paragraph"" class=""md-end-block md-p"" style=""line-height: inherit; orphans: 4; margin: 0.8em 0px; white-space: pre-wrap; position: relative; color: rgb(51, 51, 51); font-family: "Open Sans", "Clear Sans", "Helvetica Neue", Helvetica, Arial, sans-serif;""><span md-inline=""plain"" class=""md-plain"">该策略下，在调用者线程中直接执行被拒绝任务的run方法，除非线程池已经shutdown，则直接抛弃任务。</span></p>
<p cid=""n181"" mdtype=""paragraph"" class=""md-end-block md-p"" style=""line-height: inherit; orphans: 4; margin: 0.8em 0px; white-space: pre-wrap; position: relative; color: rgb(51, 51, 51); font-family: "Open Sans", "Clear Sans", "Helvetica Neue", Helvetica, Arial, sans-serif;""></p>
<p cid=""n182"" mdtype=""paragraph"" class=""md-end-block md-p"" style=""line-height: inherit; orphans: 4; margin: 0.8em 0px; white-space: pre-wrap; position: relative; color: rgb(51, 51, 51); font-family: "Open Sans", "Clear Sans", "Helvetica Neue", Helvetica, Arial, sans-serif;""><span md-inline=""plain"" class=""md-plain md-expand"">②AbortPolicy</span></p>
<p cid=""n183"" mdtype=""paragraph"" class=""md-end-block md-p"" style=""line-height: inherit; orphans: 4; margin: 0.8em 0px; white-space: pre-wrap; position: relative; color: rgb(51, 51, 51); font-family: "Open Sans", "Clear Sans", "Helvetica Neue", Helvetica, Arial, sans-serif;""><span md-inline=""plain"" class=""md-plain"">该策略下，直接丢弃任务，并抛出RejectedExecutionException异常。</span></p>
<p cid=""n184"" mdtype=""paragraph"" class=""md-end-block md-p"" style=""line-height: inherit; orphans: 4; margin: 0.8em 0px; white-space: pre-wrap; position: relative; color: rgb(51, 51, 51); font-family: "Open Sans", "Clear Sans", "Helvetica Neue", Helvetica, Arial, sans-serif;""></p>
<p cid=""n185"" mdtype=""paragraph"" class=""md-end-block md-p"" style=""line-height: inherit; orphans: 4; margin: 0.8em 0px; white-space: pre-wrap; position: relative; color: rgb(51, 51, 51); font-family: "Open Sans", "Clear Sans", "Helvetica Neue", Helvetica, Arial, sans-serif;""><span md-inline=""plain"" class=""md-plain"">③DiscardPolicy</span></p>
<p cid=""n186"" mdtype=""paragraph"" class=""md-end-block md-p"" style=""line-height: inherit; orphans: 4; margin: 0.8em 0px; white-space: pre-wrap; position: relative; color: rgb(51, 51, 51); font-family: "Open Sans", "Clear Sans", "Helvetica Neue", Helvetica, Arial, sans-serif;""><span md-inline=""plain"" class=""md-plain"">该策略下，直接丢弃任务，什么都不做。</span></p>
<p cid=""n187"" mdtype=""paragraph"" class=""md-end-block md-p"" style=""line-height: inherit; orphans: 4; margin: 0.8em 0px; white-space: pre-wrap; position: relative; color: rgb(51, 51, 51); font-family: "Open Sans", "Clear Sans", "Helvetica Neue", Helvetica, Arial, sans-serif;""></p>
<p cid=""n188"" mdtype=""paragraph"" class=""md-end-block md-p"" style=""line-height: inherit; orphans: 4; margin: 0.8em 0px; white-space: pre-wrap; position: relative; color: rgb(51, 51, 51); font-family: "Open Sans", "Clear Sans", "Helvetica Neue", Helvetica, Arial, sans-serif;""><span md-inline=""plain"" class=""md-plain"">④DiscardOldestPolicy</span></p>
<p cid=""n189"" mdtype=""paragraph"" class=""md-end-block md-p"" style=""line-height: inherit; orphans: 4; margin: 0.8em 0px; white-space: pre-wrap; position: relative; color: rgb(51, 51, 51); font-family: "Open Sans", "Clear Sans", "Helvetica Neue", Helvetica, Arial, sans-serif;""><span md-inline=""plain"" class=""md-plain md-expand"">该策略下，抛弃进入队列最早的那个任务，然后尝试把这次拒绝的任务放入队列</span></p>
<pre><code> "“`
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