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multithreading
Rafi W.
Rafi W.

Reputation: 184

Does a process run threads in a sequential order?

The question is about multithreading. Say I have 3 threads, the main one, a child1, and a child2. Does the process executing these threads run it in an order that it works on one thread for a short amount of time, then works on the other, and so on and forth and keeps switching, or are the threads running without ever being stopped by the process? Somewhere I read that a thread gets stopped without finish, then another thread is worked on and stopped, then back to thread1 and so on on forth, but that wouldn't make any sense if any threads are stopped as the point of mutlithreading was that they are all concurrent and all run at the same time, but how does the processor do that?

This is in .Net/C#.

Upvotes: 0

Views: 476

Answers (3)

John Cromartie
John Cromartie

Reputation: 4224

Operating systems schedule threads to execute on the available CPU cores (either real or virtual). In the past, most computers had single core CPUs, and thus only one thread could be executed at a time. Modern CPUs are typically 2, 4, or 8 core systems. Some of these cores are virtual, like Intel's hyperthreading CPUs which have twice as many virtual cores as physical cores.

However, there are almost always more threads than CPU cores available, so the OS will prioritize all of the threads on the system in order to run them as efficiently as possible. The threads created by your process may or may not truly run in parallel over any given time span, but you should assume that they will.

Upvotes: 0

Joachim Isaksson
Joachim Isaksson

Reputation: 180927

The scenario you're describing is correct, except that one thread will normally be running at each time per processor core.

Simplified; if 3 threads are active on 4 cores, they will all always be allowed to run since there's always an available core to run them, while if 3 threads are active on 2 cores, only two can run at any time so they will have to take turns.

Upvotes: 0

alexbuisson
alexbuisson

Reputation: 8469

the scenario you describe is the way IS ran thread in the old age before multi-core

OS scheduled thread sequentially based in their priorities, but now... I suppose you have at least 2 core where 2 thread can run concurrently and the 3rd thread will be schedule and interrupt one of the other!!!!

Upvotes: 1

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