So I was reading about Processes and Threads and I had a question. Following is the scenario.
Uniprocessor Environment
I understand that the OS rotates the processes over processor for a particular time period.(quantum) . Now I get it when the process is single threaded, ie just one path of execution. In that case, whenever it is assigned the processor, it continues with it's execution. Let's say the process forks and or just creates a new thread. Now how does the entire process works? Is it that the OS will say to process P "Go on, continue with execution" and the Process within itself will pick the new thread or the parent thread on rotation? So that if there are more than two threads, the rotation seems fair to each thread. Or does the OS actually interacts with the threads? (In that case I am not sure what happens).
Multiprocessor Environment
Now say I have a multiprocessor environment. Now in this case, if there was just uni-threaded process, then OS will assign either of the processors to it and on it will go with it's execution. Now say, there are multiple threads in the Process. Now if I assign one of the processor to the process, and ask it to continue it's execution, and the Process has to pick either of the thread for it's execution, then there never will be parallel processing going on in that specific process. Since the process will have to put either of it's threads on the processor.
So how does it happen in both the cases?
Cheers.