setrlimit() not affecting spawned std::threads

I am currently working on a pipeline which loads and transforms multiple images at once. As this is happening to many images at the same time (1440) the memory footprint is quite heavy. I therefore tried to implement a memory management system based on setrlimit, however it doesn't seem to affect the spawned threads (std::thread) as they will happily ignore the limit - I know this because of calls to getrlimit() in the threaded functions - and eventually cause my program to be killed. Here is the code I use for setting the limit:

void setMemoryLimit(std::uint64_t bytes)
{
    struct rlimit limit;
    getrlimit(RLIMIT_AS, &limit);

    if(bytes <= limit.rlim_max)
    {
        limit.rlim_cur = bytes;
        std::cout << "New memory limit: " << limit.rlim_cur << " bytes" << std::endl;
    }
    else
    {
        limit.rlim_cur = limit.rlim_max;
        std::cout << "WARNING: Memory limit couldn't be set to " << bytes << " bytes" << std::endl;
        std::cout << "New memory limit: " << limit.rlim_cur << " bytes" << std::endl;
    }

    if(setrlimit(RLIMIT_AS, &limit) != 0)
        std::perror("WARNING: memory limit couldn't be set:");

    // included for debugging purposes
    struct rlimit tmp;
    getrlimit(RLIMIT_AS, &tmp);
    std::cout << "Tmp limit: " << tmp.rlim_cur << " bytes" << std::endl; // prints the correct limit
}

I'm using Linux. The man page states that setrlimit affects the whole process so I'm kind of clueless why the threads don't seem to be affected.

Edit: By the way, the function above is called at the very beginning of main().

Solution

The problem was quite hard to find as it consisted of two entirely independent components:

My executable was compiled with -fomit-frame-pointer. This will result in a reset of the limit. See the following example:

/* rlimit.cpp */
#include <iostream>
#include <thread>
#include <vector>

#include <sys/resource.h>

class A
{
    public:
        void foo()
        {
            struct rlimit limit;
            getrlimit(RLIMIT_AS, &limit);
            std::cout << "Limit: " << limit.rlim_cur << std::endl;
        }
};

int main()
{
    struct rlimit limit;
    limit.rlim_cur = 500 * 1024 * 1024;
    setrlimit(RLIMIT_AS, &limit);
    std::cout << "Limit: " << limit.rlim_cur << std::endl;

    std::vector<std::thread> t;

    for(int i = 0; i < 5; i++)
    {
        A a;
        t.push_back(std::thread(&A::foo, &a));
    }

    for(auto thread : t)
        thread.join();

    return 0;
}

Outputs:

> g++ -std=c++11 -pthread -fomit-frame-pointer rlimit.cpp -o limit
> ./limit
Limit: 524288000
Limit: 18446744073709551615
Limit: 18446744073709551615
Limit: 18446744073709551615
Limit: 18446744073709551615
Limit: 18446744073709551615

> g++ -std=c++11 -pthread rlimit.cpp -o limit
> ./limit
Limit: 524288000
Limit: 524288000
Limit: 524288000
Limit: 524288000
Limit: 524288000
Limit: 524288000

For the image processing part I work with OpenCL. Apparently NVIDIA's implementation calls setrlimit and pushes the limit to rlim_max.