CODEWITHSUNDEEP
c++multithreadingthread-safetythreadpool
ulak blade
ulak blade

Reputation: 2665

Is it safe to use hundreds of threads if they're only created once?

Basically I have a Task and a Thread class,I create threads equal to the amount of physical cores(or logical cores,since on Intel CPU cores they're double the count).

So basically threads take tasks from a list of tasks and execute them.However,I do have to make sure everything is safe and multiple threads don't try to take the same task at once and of course this introduces extra overhead(and headaches).

What I put the tasks functionality inside the threads?I mean - instead of 4 threads grabbing tasks from a pool of 200 tasks,why not 200 threads that execute in groups of 4 by 4,basically I won't need to synchronize anything,no locking,no nothing.Of course I won't be creating the threads during the whole run-time,just at the initialization.

What pros and cons would such a method have?One problem I can thin of is - since I only create the threads at initialization,their count is fixed,while with tasks I can keep dumping more tasks in the task pool.

Upvotes: 0

Views: 150

Answers (3)

Mats Petersson
Mats Petersson

Reputation: 129454

It will definitely take longer to have 200 threads running at once than it is to run 4 threads to run 200 "tasks". You can test this by a simple program that does some simple math (e.g. calculate the first 20000000 prime, by asking each thread to do 100000 numbers at a time, then grabbing the next lot, or making 200 threads with 100000 numbers each).

How much slower? Don't know, depends on so many things.

Upvotes: 0

Remy Lebeau
Remy Lebeau

Reputation: 597111

Keeping your Task and Thread classes separate would be a cleaner and more managable approach in the long run, and keep overhead down by allowing you to limit how many Threads are created and running at any given time (also, a Task is likely to take up less memory than a Thread, and be faster to create and free when needed). A Task is what controls what gets done. A Thread is what controls when a Task is run. Yes, you would need to store the Task objects in a thread-safe list, but that is very simple to implement using a critical section, mutexe, semaphore, etc. On Windows specifically, you could alternatively use an I/O Completion Port instead to submit Tasks to Threads, and let the OS handle the synchornization and scheduling for you.

Upvotes: 0

Mike Kwan
Mike Kwan

Reputation: 24457

Threads have cost - each one requires space for a TLS and for a stack as a minimum.

Upvotes: 1

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