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Make threads faster and more reliable

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This change doubles the performance of thread spawning. That's thanks to
our new stack manager, which allows us to avoid zeroing stacks. It gives
us 15µs spawns rather than 30µs spawns on Linux. Also, pthread_exit() is
faster now, since it doesn't need to acquire the pthread GIL. On NetBSD,
that helps us avoid allocating too many semaphores. Even if that happens
we're now able to survive semaphores running out and even memory running
out, when allocating *NSYNC waiter objects. I found a lot more rare bugs
in the POSIX threads runtime that could cause things to crash, if you've
got dozens of threads all spawning and joining dozens of threads. I want
cosmo to be world class production worthy for 2025 so happy holidays all
This commit is contained in:
Justine Tunney 2024-12-18 04:59:02 -08:00
parent 906bd06a5a
commit 624573207e
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GPG key ID: BE714B4575D6E328
51 changed files with 1006 additions and 321 deletions
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25
libc/thread/pthread_exit.c
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@ -69,7 +69,7 @@
* @noreturn
*/
wontreturn void pthread_exit(void *rc) {
int orphan;
unsigned population;
struct CosmoTib *tib;
struct PosixThread *pt;
enum PosixThreadStatus status, transition;
@ -94,10 +94,21 @@ wontreturn void pthread_exit(void *rc) {
__cxa_thread_finalize();
// run atexit handlers if orphaned thread
_pthread_decimate(true);
if ((orphan = pthread_orphan_np()))
if (_weaken(__cxa_finalize))
_weaken(__cxa_finalize)(NULL);
// notice how we avoid acquiring the pthread gil
if (!(population = atomic_fetch_sub(&_pthread_count, 1) - 1)) {
// we know for certain we're an orphan. any other threads that
// exist, will terminate and clear their tid very soon. but...
// some goofball could spawn more threads from atexit handlers
for (;;) {
_pthread_decimate();
if (pthread_orphan_np()) {
if (_weaken(__cxa_finalize))
_weaken(__cxa_finalize)(NULL);
population = atomic_load(&_pthread_count);
break;
}
}
}
// transition the thread to a terminated state
status = atomic_load_explicit(&pt->pt_status, memory_order_acquire);
@ -127,7 +138,7 @@ wontreturn void pthread_exit(void *rc) {
// thread has been terminated. The behavior shall be as if the
// implementation called exit() with a zero argument at thread
// termination time." ──Quoth POSIX.1-2017
if (orphan) {
if (!population) {
for (int i = __fini_array_end - __fini_array_start; i--;)
((void (*)(void))__fini_array_start[i])();
_Exit(0);
@ -143,7 +154,7 @@ wontreturn void pthread_exit(void *rc) {
}
// this is a child thread
longjmp(pt->pt_exiter, 1);
__builtin_longjmp(pt->pt_exiter, 1);
}
__weak_reference(pthread_exit, thr_exit);