就從asynctask的構造方法開始分析
/*** creates a new asynchronous task. this constructor must be invoked on the ui thread.
*/public asynctask()
};mfuture = new futuretask(mworker) catch (interruptedexception e) catch (executionexception e) catch (cancellationexception e) }};
}可以看到在構造方法中例項化了2個成員變數mworker、mfuture。
其中workerrunnable為靜態內部類，其類宣告如下：
private static abstract class workerrunnableimplements callable
介面callable的類宣告：
public inte***ce callable
runnable 與 callable的區別：1. 是否返回結果； 2. 是否丟擲執行時異常。
futuretask的類宣告：
public class futuretaskimplements runnablefuture
其實現的介面runnablefuture的宣告：
public inte***ce runnablefutureextends runnable, future
public inte***ce runnable .
*/public void run();
}public inte***ce future
開始執行非同步任務：new asynctask(this).execute();
@mainthread
public final asynctaskexecute(params... params)
@mainthread
public final asynctaskexecuteonexecutor(executor exec,
params... params)
}mstatus = status.running;
onpreexecute();
mworker.mparams = params;
exec.execute(mfuture);
return this;}
sdefaultexecutor的定義和例項化：
public static final executor serial_executor = new serialexecutor(); //
private static volatile executorsdefaultexecutor= serial_executor;
private static internalhandler shandler;
private final workerrunnablemworker;
private final futuretaskmfuture;
private volatile status mstatus = status.pending;
private static class serialexecutor implements executor finally
}});
if (mactive == null)
}protected synchronized void schedulenext() }}
繼續**的呼叫：
會執行語句thread_pool_executor.execute(mactive);
public static final executor thread_pool_executor
= new threadpoolexecutor(core_pool_size, maximum_pool_size, keep_alive,
timeunit.seconds, spoolworkqueue, sthreadfactory);
threadpoolexecutor的
public void execute(runnable command)
if (isrunning(c) && workqueue.offer(command))
else if (!addworker(command, false))
reject(command);
}addworker(null, false)的函式簽名：
private boolean addworker(runnable firsttask, boolean core)
}boolean workerstarted = false;
boolean workeradded = false;
worker w = null;
try
} finally
if (workeradded)
}} finally
return workerstarted;}
內部類worker的宣告：
private final class worker
extends abstractqueuedsynchronizer
implements runnable
/** delegates main run loop to outer runworker. */
public void run()
// lock methods
//// the value 0 represents the unlocked state.
// the value 1 represents the locked state.
protected boolean isheldexclusively()
protected boolean tryacquire(int unused)
return false;
}protected boolean tryrelease(int unused)
public void lock()
public boolean trylock()
public void unlock()
public boolean islocked()
void interruptifstarted() catch (securityexception ignore) }}
} final void runworker(worker w) catch (runtimeexception x) catch (error x) catch (throwable x) finally
} finally
}completedabruptly = false;
} finally }
其中的task就是asynctask的成員屬性mfuture
原始碼是基於android7.0的
-> asynctask#550#execute() -> 588 -> 226#serialexecutor#execute(mfuture)
-> threadpoolexecutor#1303#execute(mfuture) -> 865$addworker(mfuture)
-> threadpoolexecutor#559#worker -> 587#run() -> 1091#runworker(worker) -> 1113#task.run();
-> asynctask#301 -> public void run()的237行 -> asynctask#290
執行asynctask的mfuture的run()
futuretask
public void run() catch (throwable ex)
if (ran)
set(result);
}} finally }
上面的c就是asynctask的屬性mworker屬性。
mworker = new workerrunnable() };
private result postresult(result result)
private static class internalhandler extends handler
@suppresswarnings()
@override
public void handlemessage(message msg) }}
如果是message_post_result分支；就執行asynctask的如下語句
private void finish(result result) else
mstatus = status.finished;}
其中更新進度的方法是後台執行緒doinbackground()方法中執行publishprogress(mcount);時呼叫父類的
@workerthread
protected final void publishprogress(progress... values) }
如果是message_post_progress分支就會呼叫onprogressupdate()，子類可以重寫該方法實現進度更新操作。
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