Thread.md

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**

	```java
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

• Blocked State

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())	

• Run State

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

• Ready State