multithreading - Can a multi-threaded program ever be deterministic?

Question

Normally it is said that multi threaded programs are non-deterministic, meaning that if it crashes it will be next to impossible to recreate the error that caused the condition. One doesn't ever really know what thread is going to run next, and when it will be preempted again.

Of course this has to do with the OS thread scheduling algorithm and the fact that one doesn't know what thread is going to be run next, and how long it will effectively run. Program execution order also plays a role as well, etc...

But what if you had the algorithm used for thread scheduling and what if you could know when what thread is running, could a multi threaded program then become "deterministic", as in, you'll be able to reproduce a crash?

Answer 1

Knowing the algorithm will not actually allow you to predict what will happen when. All kinds of delays that happen in the execution of a program or thread are dependent on environmental conditions such as: available memory, swapping, incoming interrupts, other busy tasks, etc.

If you were to map your multi-threaded program to a sequential execution, and your threads in themselves behave deterministically, then your whole program could be deterministic and 'concurrency' issues could be made reproducible. Of course, at that point they would not be concurrency issues any more.

If you would like to learn more, http://en.wikipedia.org/wiki/Process_calculus is very interesting reading.