[Solved]: Time cost of thread creation

Problem Detail: 

While creating an algorithm, the following question came up:

In uniform cost, what is the time cost of a process that creates a thread?

Is there a difference between creating a thread in a thread pool vs creating a thread in runtime?

I know these questions should be self-explanatory, but I cannot seem to find an answer.

Asked By : user3129956

Answered By : Wandering Logic

The cost of thread creation is constant but large on most real systems. (Think approximately the same cost as doing 1000 function calls of a function that does nothing but return a small constant. On most systems it requires a call into the kernel, which is pretty expensive.)

The point of a thread pool is to try to amortize this large constant cost over multiple thread creation/destruction requests. A thread pool is an abstraction that caches threads that are currently not in use, thus can be allocated relatively quickly instead of going through the enormous cost of creating a new thread. A typical thread pool might work as follows:

• starts out empty
• if a request is made for a thread from the pool and the pool is currently empty, then create a new thread and return it to the requester.
• if a request is made to "exit" a thread, then instead of really shutting the thread down you insert a pointer to the thread into the thread pool and put the thread to sleep.
• if a request is made for a thread from the pool and the pool contains a sleeping thread, then wake the thread up, give it the requested work, and return the pointer to the thread to the requester.

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Question Source : http://cs.stackexchange.com/questions/25888