Thread Back

• Thread(線程)指一個程序中的執行片段,且擁有併發執行的特性.
• 線程間通信可通過共享全局變量來實現

同步&互斥

• 同步: 指事件處理存在一定的協作順序，而這個順序的改變將會導致結果的差錯. (Semaphore)
• 互斥: 指多個進程將要讀取同一區域(關鍵區)的數據時,將只能允許一個進程進入. (Mutex)

Ways to create a thread

• Inherit from the calss Thread (java.lang.Thread)

class MyThread extends Thread
{
    //Attributes
    MyThread()
    {
        //Constructor
    }

    @SuppressWarnings("deprecation")
    public void run()
    {
        //What you want this thread to do
    }
}

• implements Runnable interface

  • with this

    class MyThread implements Runnable
    {
      Thread t;
      MyThread()
      {
          t = new Thread(this);
          t.start()；
      }
    
      //Implements
      public void run() 
      {
          //What you want this thread to do
      }
    }
    

  • with unnamed inner class

    Thread MyThread = new Thread(
    new Runnable()
    {
      public void run()
      {
          //What you want this thread to do
      }
    });
    

some methods of Threads

• join()

t.join();    //Wait for this thread to die

• yield()

t.yield();    //Causes the currently executing thread object to temporarily pause 
        //and allow other threads to execute.

• setPriority(int newPriority)

t.setPriorty(MAX_PRIORITY);    //Changes the priority of this thread to a max one

/*    java.lang.Thread
*    public static final int    MAX_PRIORITY    10
*    public static final int    MIN_PRIORITY    1
*    public static final int    NORM_PRIORITY    5
*/

When sharing same datas

/* do with shared datas */
public synchronized void transfer()
{  
    //synchronized label ensures that this thread won't be schedule out when running this method.
}

States of a Thread

1. Process blocks for input
2. Scheduler picks another process
3. Scheduler picks this process
4. Input becomes available

Thread.sleep(100);    //Blocked State (do not release lock)

@Deprecated
Thread.suspend();    

wait();            //Blocked State (release lock and need other threads to call notify() or notifyall())

Thread t = new MyThread()    //Initialize
t.start();    //Run State
            //Ready State: Waiting CPU to call it