future是concurrent包提供的一種非同步得到結果的介面。
future介面：
public
inte***ce
future
callable介面：
public
inte***ce
callable
private
volatile
int state;
private
static
final
int new =0;
//初始
private
static
final
int completing =1;
//任務已經執行完或者出錯，準備賦值
private
static
final
int normal =2;
//任務正常執行完，並且已經賦值完
private
static
final
int exceptional =3;
//任務失敗，把異常賦值回去
private
static
final
int cancelled =4;
//取消
private
static
final
int interrupting =5;
//準備中斷計算過程
private
static
final
int interrupted =6;
//對計算進行中斷
futuretask的實現介面：
測試**：
public
class
testmain};
futuretask
futuretask =
newfuturetask
(callable)
;new
thread
(futuretask)
.start()
; dishes dishes =
newdishes()
; dishes.
washdishes()
; clothes clothes = null;
trycatch
(interruptedexception e)
catch
(executionexception e)
if(clothes != null)
long end = system.
currenttimemillis()
; system.out.
println
("all tasks cost "
+(end - start)
+" millis");
/*執行結果：
start to wash dishes
machine starts to wash cloths
all dishes are cleaned!!!
all clothes are cleaned!!!
**********=over**********=
all tasks cost 3003 millis
*/}static
class
clothes
catch
(interruptedexception e)
system.out.
println
("all clothes are cleaned!!!");
}}static
class
dishes
catch
(interruptedexception e)
system.out.
println
("all dishes are cleaned!!!");}}}
在**的最開頭，我們new了乙個callable物件，callable物件會被當做任務丟到futuretask裡面執行。
啟動執行緒就可以開始執行任務了。
下面具體說一下future幫我們幹了什麼，為什麼他是非同步的。
public
void
run(
)catch
(throwable ex)
if(ran)
set(result);}
}finally
}
set方法會呼叫finishcompletion，
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;}
}done()
;// protected方法，鉤子函式，留給程式設計師自己實現
callable = null;
// to reduce footprint
}
public v get()
throws interruptedexception, executionexception
private
intawaitdone
(boolean timed,
long nanos)
throws interruptedexception
int s = state;
if(s > completing)
// completing是乙個很短暫的狀態，呼叫thread.yield期望讓出時間片，之後重試迴圈
else
if(s == completing)
// cannot time out yet
thread.
yield()
;else
if(q == null)
q =newwaitnode()
;elseif(
!queued)
/* 當前節點未入棧
* 這是treiber stack演算法入棧的邏輯。
* treiber stack是乙個基於cas的無鎖併發棧實現,
*/queued = unsafe.
compareandswapobject
(this
, waitersoffset,
q.next = waiters, q)
;else
if(timed)
locksupport.
parknanos
(this
, nanos);}
else
//這裡阻塞住
locksupport.
park
(this);
}}
private v report
(int s)
throws executionexception
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