static void *mill_allocstackmem(void) {
void *ptr;
#if defined HAVE_POSIX_MEMALIGN && HAVE_MPROTECT
/* Allocate the stack so that it's memory-page-aligned. */
int rc = posix_memalign(&ptr, mill_page_size(), mill_get_stack_size());
if(mill_slow(rc != 0)) {
errno = rc;
return NULL;
}
/* The bottom page is used as a stack guard. This way stack overflow will
cause segfault rather than randomly overwrite the heap. */
rc = mprotect(ptr, mill_page_size(), PROT_NONE);
if(mill_slow(rc != 0)) {
int err = errno;
free(ptr);
errno = err;
return NULL;
}
#else
ptr = malloc(mill_get_stack_size());
if(mill_slow(!ptr)) {
errno = ENOMEM;
return NULL;
}
#endif
return (void*)(((char*)ptr) + mill_get_stack_size());
}
void mill_preparestacks(int count, size_t stack_size) {
/* Purge the cached stacks. */
while(1) {
struct mill_slist_item *item = mill_slist_pop(&mill_cached_stacks);
if(!item)
break;
free(((char*)(item + 1)) - mill_get_stack_size());
}
/* Now that there are no stacks allocated, we can adjust the stack size. */
size_t old_stack_size = mill_stack_size;
size_t old_sanitised_stack_size = mill_sanitised_stack_size;
mill_stack_size = stack_size;
mill_sanitised_stack_size = 0;
/* Allocate the new stacks. */
int i;
for(i = 0; i != count; ++i) {
void *ptr = mill_allocstackmem();
if(!ptr) goto error;
struct mill_slist_item *item = ((struct mill_slist_item*)ptr) - 1;
mill_slist_push_back(&mill_cached_stacks, item);
}
mill_num_cached_stacks = count;
/* Make sure that the stacks won't get deallocated even if they aren't used
at the moment. */
mill_max_cached_stacks = count;
errno = 0;
return;
error:
/* If we can't allocate all the stacks, allocate none, restore state and
return error. */
while(1) {
struct mill_slist_item *item = mill_slist_pop(&mill_cached_stacks);
if(!item)
break;
free(((char*)(item + 1)) - mill_get_stack_size());
}
mill_num_cached_stacks = 0;
mill_stack_size = old_stack_size;
mill_sanitised_stack_size = old_sanitised_stack_size;
errno = ENOMEM;
}
void *mill_allocstack(size_t *stack_size) {
if(!mill_slist_empty(&mill_cached_stacks)) {
--mill_num_cached_stacks;
return (void*)(mill_slist_pop(&mill_cached_stacks) + 1);
}
void *ptr = mill_allocstackmem();
if(!ptr)
mill_panic("not enough memory to allocate coroutine stack");
if(stack_size)
*stack_size = mill_get_stack_size();
return ptr;
}
void mill_freestack(void *stack) {
/* Put the stack to the list of cached stacks. */
struct mill_slist_item *item = ((struct mill_slist_item*)stack) - 1;
mill_slist_push_back(&mill_cached_stacks, item);
if(mill_num_cached_stacks < mill_max_cached_stacks) {
++mill_num_cached_stacks;
return;
}
/* We can't deallocate the stack we are running on at the moment.
Standard C free() is not required to work when it deallocates its
own stack from underneath itself. Instead, we'll deallocate one of
the unused cached stacks. */
item = mill_slist_pop(&mill_cached_stacks);
void *ptr = ((char*)(item + 1)) - mill_get_stack_size();
#if HAVE_POSIX_MEMALIGN && HAVE_MPROTECT
int rc = mprotect(ptr, mill_page_size(), PROT_READ|PROT_WRITE);
mill_assert(rc == 0);
#endif
free(ptr);
}
