FutureTask源碼學習

FutureTask源碼

    FutureTask是一個可以用來監控Callable執行狀況的類
    我們首先來看一下它是如何實現監控的:

 

     

     public void run() { 

        if (state != NEW || 

            !UNSAFE.compareAndSwapObject(this, runnerOffset, 

                                         null, Thread.currentThread())) 

            return; 

        try { 

            Callable c = callable; 

            if (c != null && state == NEW) { 

                V result; 

                boolean ran; 

                try { 

                    result = c.call(); 

                    ran = true; 

                } catch (Throwable ex) { 

                    result = null; 

                    ran = false; 

                    setException(ex); 

                } 

                if (ran) 

                    set(result); 

            } 

        } finally { 

            // runner must be non-null until state is settled to 

            // prevent concurrent calls to run() 

            runner = null; 

            // state must be re-read after nulling runner to prevent 

            // leaked interrupts 

            int s = state; 

            if (s >= INTERRUPTING) 

                handlePossibleCancellationInterrupt(s); 

        } 

    } 

     

    

    FutureTask覆蓋了Runnable的run()方法，因此也算是一個線程，首先它獲取callable，然後執行callable,然後修改callable的狀態。根據callable的狀態即可監控callable的狀態。