thread priority question.

[Minhaj Mehmood]

Which of the following statements about this program are correct?

class CoolThread extends Thread
{
	String id = "";
	public CoolThread(String s){ this.id = s; }
	public void run()
	{
		System.out.println(id+"End");
	}
	public static void main(String args [])
	{
		Thread t1 = new CoolThread("AAA");
		t1.setPriority(Thread.MIN_PRIORITY);
		Thread t2 = new CoolThread("BBB");
		t2.setPriority(Thread.MAX_PRIORITY);
		t1.start(); t2.start();
	}
}

a "AAA End" will always be printed before "BBB End".


b "BBB End" will always be printed before "AAA End".


c The order of "AAA End" and "BBB End" cannot be determined.


d The program will not compile.


e THe program will throw an exception at runtime.

--
ref: jqplus

[Minhaj Mehmood]

well the answer is "c" but why its not "a" in fact we are setting the priorities of threads!!
this is something really confusing

[Ankit Garg]

Setting a thread's priority doesn't guarantee that the higher priority thread will run before the lower priority thread. You can read tutorials on thread priorities. Like this tutorial which says:

Rule of thumb: At any given time, the highest priority thread is running. However, this is not guaranteed. The thread scheduler may choose to run a lower priority thread to avoid starvation. For this reason, use priority only to affect scheduling policy for efficiency purposes. Do not rely on thread priority for algorithm correctness.

[Minhaj Mehmood]

good one ankit - thanks, addition to above: following explanation given by simulator

In this case, the program is trying to manipulate the scheduling of thread using priorities which is a bad idea. Simply because operating systems behave differently about prioities. For ex. Win32 uses Time Slicing ie. it gives time to all the thread in proportion of their priorites but many unix systems do not let low priority threads run at all if a higher priority thread is running. So the output cannot be determined.