CODEWITHSUNDEEP
multithreadingconcurrencyoperating-systemcreation
coderodde
coderodde

Reputation: 977

Can thread creation within OS internals run concurrently?

Suppose we have a dual-core machine with a mainstream, modern OS capable to utilize both the cores. If I have two threads, P1 and Q1 within the same process, and they happen to commence creating child threads, say, P2 and Q2, at approximately the same machine cycle, will OS perform the thread creation concurrently?

I heard thread creation is expensive, so the question came forth...

Thanks in advance.

Upvotes: 0

Views: 107

Answers (2)

Martin James
Martin James

Reputation: 24857

It will be sorta-concurrently. There are aspects of thread-creation that cannot proceed in parallel - it would be unfortunate if the kernel memory-manager allocated both threads the same stack!

Thread creation is sufficiently expensive that it's worth while avoiding doing it at all during an app. run, hence the popularity of thread pools. Long-running tasks that block can be threaded off and left for the life of the app - often this means that explicit thread termination, (awkward at best, almost impossible at worst, from user code), is not necessary.

I think developers continually start and stop threads because they like to think of them as 'functions', where you 'pass parameters' in at the start and 'return' results when the thread ends. Ths is not the best way of conceptualizing threads.

Upvotes: 0

Kaz
Kaz

Reputation: 58578

Any reasonably well designed OS can have multiple processors executing kernel code at the same time. Therefore some of the tasks involved in a thread creation can be happening concurrently. But there will be some necessary serialization to manipulate some shared data structures (e.g. allocating memory, inserting a newly created threat structure into a global list). The processors could contend for the same lock thereby reducing concurrency.

Systems/applications which make new threads so often that the overhead of thread creation actually matters are probably designed wrong (doing too little useful work in a thread relative to the startup time, and not taking advantage of the obvious optimization of reusing short-lived threads from a pool).

Upvotes: 2

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