Beginner Java Multi-Threaded Programming: Scheduling Difference between Window and Mac

Question

Background I am a CS student and today in class we learned Multi-Threaded Programming in Java. The professor asked students to write a simple program to demonstrate the scheduling of threads. Every student had this piece of code: ``` public class MyThread extends Thread { private int num; public MyThread(int num) { this.num = num; } public void run() { System.out.println("Thread " + num + " is starting."); } public static void main( String [] args ) { for (int i=0; i<100; i++) { MyThread mt = new MyThread(i); mt.start(); } } } ``` Expectation Since threads don't necessarily execute in sequential time, we were expecting the line Thread `i` is starting to not be in strictly 0, 1, 2... to 99 order. Instead, we were expecting something like Thread 0 is starting Thread 5 is starting Thread 2 is starting ... (ninety lines later) Thread 95 is starting Thread 99 is starting Thread 98 is starting (Program finishes running) Question Interestingly, while Windows users seem to have the pattern as…

Accepted Answer

Why do Mac and Windows behave differently?

The thread scheduling is based on the internals of the operating system. All you can say is that Mac OSX and Windows behave differently as they are different operating systems. if you have different hardware, this will also make a difference.

Is this related to the scheduling algorithms used?

Creating a thread is very expensive and your task is very short lived so it is unlikely you will see the effect of scheduling in this case. really you are testing how threads are created.

If so, what are the algorithms and how might this affect other JVM Multi-threaded programs?

You need to look at the internals of the OS.

The effect on a well written JVM program should none at all. You should write programs which are not sensitive to subtle differences in how a particular OS or hardware operates.

You also shouldn't create threads like mad and this is obviously inefficient. Speculating on how a poorly written, or inefficient program operates isn't very useful.

I suggest starting with a problem which performs better with multiple threads than with one (in your example one thread would be more efficient) and see if scheduling has an impact on a range of CPU types.

Beginner Java Multi-Threaded Programming: Scheduling Difference between Window and Mac

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