Java-技術專題-多線程之線程池

{"type":"doc","content":[{"type":"heading","attrs":{"align":null,"level":3},"content":[{"type":"text","text":"一、線程池的構造"}]},{"type":"paragraph","attrs":{"indent":1,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"使用線程池離不開ThreadPoolExecutor類，該類實現了ExecutorService接口，其構造方法如下："}]},{"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":"參數說明如下："}]},{"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：線程池大小（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：沒有任務時線程的存活時間，默認情況下只有線程數目大於corePoolSize時，此參數才起作用，若線程數目等於corePoolSize，則這些線程會一直存活。但若調用allowCoreThreadTimeOut(boolean)方法，則線程數目不大於corePoolSize時，此參數也起作用，直到線程數目爲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的時間單位，有以下七種取值："}]},{"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;//小時"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"TimeUnit.MINUTES;//分鐘"}]},{"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;//納秒"}]}]},{"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：指定構成緩衝區的阻塞隊列，即指定了線程池的排隊策略，常用的有以下三種："}]},{"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：基於數組的先進先出隊列，此隊列創建時必須指定大小"}]},{"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：基於鏈表的先進先出隊列，如果創建時沒有指定此隊列大小，則默認爲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：這個隊列不會保存提交的任務，而是將直接新建一個線程來執行新來的任務"}]}]},{"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（可選）：線程工廠，用來創建線程，可自定義"}]},{"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（可選）：拒絕策略，有以下四種策略可選："}]},{"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:丟棄任務並拋出RejectedExecutionException異常。"}]},{"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：丟棄任務，不拋出異常。"}]},{"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：丟棄隊列最前面的任務，然後重新嘗試執行任務"}]},{"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：由調用線程處理該任務"}]}]},{"type":"heading","attrs":{"align":null,"level":3},"content":[{"type":"text","text":"二、線程池的運行過程"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":" 如果當前線程池中的線程數目小於corePoolSize，則每來一個任務，就會創建一個線程去執行這個任務如果當前線程池中的線程數目>=corePoolSize，則每來一個任務，會嘗試將其添加到任務緩存隊列當中，若添加成功，則該任務會等待空閒線程將其取出去執行；若添加失敗（一般來說是任務緩存隊列已滿），則會嘗試創建新的線程去執行這個任務"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":" 如果當前線程池中的線程數目達到maximumPoolSize，則會採取任務拒絕策略進行處理"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"如果線程池中的線程數量大於"},{"type":"text","marks":[{"type":"strong"}],"text":"corePoolSize"},{"type":"text","text":"時，如果某線程空閒時間超過keepAliveTime，線程將被終止，直至線程池中的線程數目不大於corePoolSize；"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":" 如果允許爲核心池中的線程設置存活時間（調用"},{"type":"codeinline","content":[{"type":"text","text":"allowCoreThreadTimeOut(boolean)"}]},{"type":"text","text":"方法），那麼核心池中的線程空閒時間超過keepAliveTime，線程也會被終止"}]},{"type":"heading","attrs":{"align":null,"level":3},"content":[{"type":"text","text":"三、線程的初始化"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":" 默認情況下，線程池構造完成後是沒有線程的，需要等任務提交時纔會創建線程，如果需要在線程池構造完成時就創建線程，可以調用以下兩個方法："}]},{"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()：初始化一個核心線程；"}]},{"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()：初始化所有核心線程"}]},{"type":"heading","attrs":{"align":null,"level":3},"content":[{"type":"text","text":"四、線程池的關閉"}]},{"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()：不會立即關閉線程池，而是不再接受新的任務，等當前所有任務處理完之後關閉線程池"}]},{"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()：立即關閉線程池，打斷正在執行的任務，清空緩衝隊列，返回尚未執行的任務"}]},{"type":"heading","attrs":{"align":null,"level":3},"content":[{"type":"text","text":"五、任務提交"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"任務提交有兩種方法，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)，無返回值"}]},{"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、可選線程池模型（Executors類的靜態工廠方法）"}]},{"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":"調用實例："},{"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":"構造線程池時優先選用線程池模型，如果這些模型不能滿足要求，再自定義ThreadPoolExecutor線程池"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}}]}