Determining Process Stack Limits

Since certain system defaults and limits can change between releases of Mac OS X, it is useful to be able to determine the default process stack size for the system you are developing on. From the command line, limit (csh, tcsh) or ulimit -a (sh, bash) will output a variety of system defaults including the default process stack size.

Alternately, the system-defined default and maximum process stack sizes can be obtained using the getrlimit function call. See the Darwin man page for getrlimit for more information.

Setting a Larger Stack at Link Time

If you find your application is crashing because it is outgrowing the default 8 Megabyte stack allocation, you can raise its default by passing the -stack_size flag on the link line and specifying a new stack size up to 64 Megabytes.

Dynamically Growing The Process Stack at Runtime

Using the BSD system call setrlimit, you can increase the stack size of a process up to the size allowed by the system. See the Darwin man page for setrlimit for more information.

Setting The Stack Size for an Individual Thread

You can also increase the stack size allocated to threads as you create them. In Pthreads this is done by setting up a custom attribute and passing it to pthread_create.

Listing 1  Setting a Pthread's Stack Size

#include <limits.h>
#include <pthread.h>

#define REQUIRED_STACK_SIZE 1024*1024

int CreateThreadWithLargeStack (pthread_t *outThread, void *threadFunc, void *arg)
{
    int 			err = 0;
    pthread_attr_t 	stackSizeAttribute;
    size_t			stackSize = 0;

    /*  Initialize the attribute */
    err = pthread_attr_init (&stackSizeAttribute);
    if (err) return (err);

    /* Get the default value */
    err = pthread_attr_getstacksize(&stackSizeAttribute, &stackSize); 
    if (err) return (err);

    /* If the default size does not fit our needs, set the attribute with our required value */
    if (stackSize < REQUIRED_STACK_SIZE)
    {
        err = pthread_attr_setstacksize (&stackSizeAttribute, REQUIRED_STACK_SIZE);
        if (err) return (err);
    }

    /*  Create the thread with our attribute */
    err = pthread_create (outThread, &stackSizeAttribute, threadFunc, arg);
    return (err);
}