Java Thread Notes

進入waiting queue的兩種可能:
1. 被lock (synchronized block) 擋在critical section外面.
2. call wait() method.

離開waiting queure的可能:
1.call notify() method.
2.call notifyAll() method.
3.call interrupt() method.
4.time out occur. (透過call wait( long time ) 來實現)

yield() v.s. sleep() v.s. wait() v.s. join()
1. yield() thread 沒有離開monitor，只是暫時將執行權交給其它的thread (content switch ?)
2. sleep(1000)，thread 沒有離開monitor, 只是暫停執行1000ms.
3. wait(1000) ，thread離開monitor, 移到waiting queue, 若1000ms後仍未被喚醒, 便離開waiting queue, 重新競爭lock；若無設time out，即wait()，則移至waiting queue等待。直到notify(), notifyAll(), interrupt() 被呼叫時，才會便離開waiting queue, 重新競爭lock.
4. join()，直到此thread執行完，才將執行權讓出。也可設time out。

interrupt()　把沈睡的thread半途打醒.
1. 用來中斷wait(), sleep(), join()等狀態的thread.
2. 會從wait(), sleep(), join() 中丟出InterruptedException, thread的控制權便會轉入catch block.
3. thread wati()時，會離開monitor，移到waiting queue，所以當wait狀態的thread被呼叫interrupt()時，需先重新搶到lock，才會丟出interruptedException. 取得lock前都不會丟出interruptedException.
4. wait(), sleep(), join()都會不斷檢查interrupt status，而interrupt()便是把interrupt status設為true，當wait(), sleep(), join()發現interrupt status為true時，便丟出interruptedException.
5. isInterrupted() 可以回傳interrupt status為何.
6. interrupted() 除了回傳interrupt status外，並將interrupt status設為false.

interrupt() v.s. notify() and notifyAll()
1.notify()及notifyAll()是喚醒在waiting queue的thread.
2.interrupt()是直接中斷sleep() , wait(), join()狀態的thread.