It has been noted by people doing testing on Linux systems that
ulimit -s unlimited
python Misc/find_recursionlimit.py
will run for a *long* time if you have built Python without threads, but
will die after about 2400/2500 iterations if you have built with
threads, regardless of the "ulimit" setting.
I had thought this was evidence of a bug in Pthreads. In fact
(although we still have other reasons to suspect Pthread bugs),
the behavior is easily explained. The function "pthread_initialize"
in pthread.c contains this very lovely code:
/* Play with the stack size limit to make sure that no stack ever grows
beyond STACK_SIZE minus two pages (one page for the thread descriptor
immediately beyond, and one page to act as a guard page). */
getrlimit(RLIMIT_STACK, &limit);
max_stack = STACK_SIZE - 2 * __getpagesize();
if (limit.rlim_cur > max_stack) {
limit.rlim_cur = max_stack;
setrlimit(RLIMIT_STACK, &limit);
}
In "internals.h", STACK_SIZE is #defined to (2 * 1024 * 1024)
So whenever you're using threads, you have an effective rlimit of 2MB
for stack, regardless of what you may *think* you have set via
"ulimit -s"
One more mystery explained!
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