Building Your Own Stack

When you specify the size of a thread stack, be sure to account for the allocations needed by the invoked function and by each function called. The accounting should include calling sequence needs, local variables, and information structures.

Occasionally you want a stack that is a bit different from the default stack. An obvious situation is when the thread needs more than one megabyte of stack space. A less obvious situation is when the default stack is too large. You might be creating thousands of threads and not have enough virtual memory to handle the gigabytes of stack space that this many default stacks require.

The limits on the maximum size of a stack are often obvious, but what about the limits on its minimum size? There must be enough stack space to handle all of the stack frames that are pushed onto the stack, along with their local variables, and so on.

You can get the absolute minimum limit on stack size by calling the macro PTHREAD_STACK_MIN, which returns the amount of stack space required for a thread that executes a NULL procedure. Useful threads need more than this, so be very careful when reducing the stack size.

#include <pthread.h>

pthread_attr_t tattr;
pthread_t tid;
int ret;

int size = PTHREAD_STACK_MIN + 0x4000;

/* initialized with default attributes */
ret = pthread_attr_init(&tattr);

/* setting the size of the stack also */
ret = pthread_attr_setstacksize(&tattr, size);

/* only size specified in tattr*/
ret = pthread_create(&tid, &tattr, start_routine, arg); 

When you allocate your own stack, be sure to append a red zone to its end by calling mprotect(2).