FutureTask原始碼閱讀與理解

futuretask原始碼閱讀與理解

簡述：futuretask實現了runnable和future介面，代表此類可以被執行緒池排程和非同步執行任務。

幾個變數：

//以下是state的幾種狀態

private
volatile
int state;
private
static
final
int new          = 0;
private
static
final
int completing   = 1;
private
static
final
int normal       = 2;
private
static
final
int exceptional  = 3;
private
static
final
int cancelled    = 4;
private
static
final
int interrupting = 5;
private
static
final
int interrupted  = 6;
//具體任務
private callablecallable;
//任務執行完畢結果存放屬性
private object outcome; 
//記錄執行任務的執行緒
private
volatile thread runner;
//鍊錶結構，表示等待結果的執行緒
private
volatile waitnode waiters;

//run方法就是執行任務的方法

public
void
run()  catch (throwable ex) 
//如果執行成功則執行set方法
if (ran)
set(result);
}} finally 
}protected
void
set(v v) 
}private
void
finishcompletion() 
waitnode next = q.next;
if (next == null)
break;
q.next = null; // unlink to help gc
q = next;
}break;}}
//完成任務並喚醒所有等待結果執行緒再執行done方法
done();
callable = null;        // to reduce footprint
}//獲取資料的方法，可限時：
public v get() throws interruptedexception, executionexception 
public v get(long timeout, timeunit unit)
throws interruptedexception, executionexception, timeoutexception 
//具體的取值-等待方法
private
intawaitdone(boolean timed, long nanos)
throws interruptedexception 
//如果大於已完成則返回
int s = state;
if (s > completing) 
//說明執行任務的執行緒正在給outcome賦值，讓掉cpu
else
if (s == completing) // cannot time out yet
thread.yield();
//如果q==null那就建立乙個等待節點
else
if (q == null)
q = new waitnode();
//試著加入佇列
else
if (!queued)
queued = unsafe.compareandswapobject(this, waitersoffset,q.next = waiters, q);
//是否有設定超時時間
else
if (timed) 
locksupport.parknanos(this, nanos);
}//掛起執行緒
else
locksupport.park(this);
}}

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