How to set the stacksize with C++11 std::thread

I've been trying to familiarize myself with the std::thread library in C++11, and have arrived at a stumbling block.

Initially I come from a posix threads background, and was wondering how does one setup the stack size of the std::thread prior to construction, as I can't seem to find any references to performing such a task.

Using pthreads setting the stack size is done like this:

void* foo(void* arg);
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pthread_attr_t attribute;
pthread_t thread;

pthread_attr_init(&attribute);
pthread_attr_setstacksize(&attribute,1024);
pthread_create(&thread,&attribute,foo,0);
pthread_join(thread,0);

Is there something similar when using std::thread?

I've been using the following reference:

http://en.cppreference.com/w/cpp/thread

Solution 1:

Initially I come from a posix threads background, and was wondering how does one setup the stack size of the std::thread prior to construction, as I can't seem to find any references to performing such a task.

You can't. std::thread doesn't support this because std::thread is standardized, and C++ does not require that a machine even has a stack, much less a fixed-size one.

pthreads are more restrictive in terms of the hardware that they support, and it assumes that there is some fixed stack size per thread. (So you can configure this)

Solution 2:

As Loki Astari already said, it is extremely rare to actually need a non-default stack-size and usually either a mistake or the result of bad coding.

• If you feel like the default stack size is too big for your needs and want to reduce it, just forget about it. Every modern OS now uses virtual memory / on-demand commit, which means that memory is only reserved, not actually allocated, until you access the pages. Reducing the stack size will not reduce your actual memory footprint.

• Due to this very behaviour, OSes can afford to set the default stack size to very big values. E.g. on a vanilla Debian this is 8MB (ulimit -s) which should be enough for every need. If you still manage to hit that limit, my first idea would be that your code is wrong, so you should first and foremost review it and move things to the heap, transform recursive functions into loops, etc.

• If despite all of this you really really need to change the stack size (i.e. increase it, since reducing it is useless), on POSIX you can always use setrlimit at the start of your program to increase the default stack size. Sure this will affect all threads, but only the ones who need it will actually use the additional memory.

• Last but not least, in all fairness I can see a corner case where reducing the stack size would make sense: if you have tons of threads on a 32 bits system, they could eat up your virtual address space (again, not the actual memory consumption) up to the point that you don't have enough address space available for the heap. Again, setrlimit is your friend here even though I'd advise to move to a 64 bits system to benefit from the larger virtual address space (and if your program is that big anyway, you'll probably benefit from the additional RAM too).