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multithreadingthreadpool
yash
yash

Reputation: 23

Number of threads in a thread pool

I have two questions.. 1. What is he difference between thread and thread pool? Can I have multiple thread pools (not threads) in my system. 2. I have been reading that general size of a threads in a thread pool is to be same as the number of processors or one more than the processor. I am using a quad core processor, that means I can have 4 or 5 threads in a thread pool. However under task manager my system shows more than 1000 threads active anytime..??

Upvotes: 1

Views: 5881

Answers (1)

Jeremy Friesner
Jeremy Friesner

Reputation: 73041

  1. What is he difference between thread and thread pool?

A thread is a single flow of execution. A thread pool is a group of these threads; usually the threads in a thread pool are kept alive indefinitely (i.e. until program shutdown) so that as each new work-request comes in, it can be handed to the next available thread in the thread-pool for processing. (This is beneficial because it's more efficient to just wake up an existing thread and hand it some work than it is to always create a new thread every time a new work-request comes in, and then destroy the thread afterwards)

Can I have multiple thread pools (not threads) in my system.

Yes.

  1. I have been reading that general size of a threads in a thread pool is to be same as the number of processors or one more than the processor.

That's a good heuristic, but it's not a requirement; your thread pool can have as many or as few threads in it as you like. The reason people suggest that number is that if you have fewer threads in your thread pool than you have physical CPU cores, then under heavy load not all of your CPU cores will get used (e.g. if you have a 3-thread pool and 4 CPU cores, then under heavy load you'll have 3 CPU cores busy and 1 CPU core idle/wasted, and your program will take ~25% longer to finish the work than if it would have if it had 4 threads in the pool). On the other hand, if you have more threads than CPU cores, then under heavy load the "extra" threads merely end up time-sharing a CPU core together, slowing each other down and not providing any additional benefit in terms of work-completion-rate.

However under task manager my system shows more than 1000 threads active anytime..??

The thing to notice about those 1000 threads is that probably 99% of them are actually asleep at any given moment. Most threads aren't doing work all the time; rather they spend most of their lives waiting for some particular event to occur, quickly handling it, and then going back to sleep until the next event comes along for them to handle. That's the reason why you can have 1000 threads present on just a handful of CPU cores without everything bogging down.

Upvotes: 11

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