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Remove timeout slicing from __timedwait. NFC #26550

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Merged
sbc100 merged 1 commit into from
Mar 26, 2026
+25 −53
Merged

Remove timeout slicing from __timedwait. NFC #26550

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37 changes: 2 additions & 35 deletions system/lib/libc/musl/src/thread/__timedwait.c
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Original file line number Diff line number Diff line change
Expand Up @@ -58,41 +58,8 @@ int __timedwait_cp(volatile int *addr, int val,
}

#ifdef __EMSCRIPTEN__
double msecsToSleep = top ? (top->tv_sec * 1000 + top->tv_nsec / 1000000.0) : INFINITY;

// cp suffix in the function name means "cancellation point", so this wait can be cancelled
// by the user, unless current thread has cancelation disabled (which may be either done
// directly, or indirectly, for example in the __timedwait() function).
pthread_t self = pthread_self();

if (self->canceldisable != PTHREAD_CANCEL_DISABLE) {
double max_ms_slice_to_sleep = 100;
double sleepUntilTime = emscripten_get_now() + msecsToSleep;
do {
if (self->cancel) {
// The thread was canceled by pthread_cancel().
// In the case of cancelasync or PTHREAD_CANCEL_ENABLE we can just call
// __pthread_testcancel(), which won't return at all.
__pthread_testcancel();
// If __pthread_testcancel does return here it means that canceldisable
// must be set to PTHREAD_CANCEL_MASKED. In this case we emulate the
// behaviour of the futex syscall and return ECANCELLED here.
// See pthread_cond_timedwait.c for the only use of this flag.
return ECANCELED;
}
msecsToSleep = sleepUntilTime - emscripten_get_now();
if (msecsToSleep <= 0) {
return ETIMEDOUT;
}
// Must wait in slices in case this thread is cancelled in between.
if (msecsToSleep > max_ms_slice_to_sleep)
msecsToSleep = max_ms_slice_to_sleep;
r = -emscripten_futex_wait((void*)addr, val, msecsToSleep);
} while (r == ETIMEDOUT);
} else {
// Can wait in one go.
r = -emscripten_futex_wait((void*)addr, val, msecsToSleep);
}
double msecs_to_sleep = top ? (top->tv_sec * 1000 + top->tv_nsec / 1000000.0) : INFINITY;
r = -emscripten_futex_wait((void*)addr, val, msecs_to_sleep);
#else
r = -__futex4_cp(addr, FUTEX_WAIT|priv, val, top);
#endif
Expand Down
9 changes: 7 additions & 2 deletions system/lib/pthread/emscripten_futex_wait.c
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Original file line number Diff line number Diff line change
Expand Up @@ -132,7 +132,7 @@ int emscripten_futex_wait(volatile void *addr, uint32_t val, double max_wait_ms)

#ifdef __EMSCRIPTEN_PTHREADS__
pthread_t self = pthread_self();
bool cancelable = !self->canceldisable && self->cancelasync;
bool cancelable = self->canceldisable != PTHREAD_CANCEL_DISABLE;
#else
bool cancelable = false;
#endif
Expand Down Expand Up @@ -215,7 +215,12 @@ int emscripten_futex_wait(volatile void *addr, uint32_t val, double max_wait_ms)
#ifdef __EMSCRIPTEN_PTHREADS__
if (cancelable && ret == ATOMICS_WAIT_TIMED_OUT && self->cancel) {
__pthread_testcancel();
break;
// If __pthread_testcancel does return here it means that canceldisable
// must be set to PTHREAD_CANCEL_MASKED. In this case we emulate the
// behaviour of the futex syscall and return ECANCELLED here.
// See pthread_cond_timedwait.c for the only use of this flag.
emscripten_conditional_set_current_thread_status(EM_THREAD_STATUS_WAITFUTEX, EM_THREAD_STATUS_RUNNING);
return -ECANCELED;
}
// If remainder_ns is negative it means we want wait forever, and we don't
// need to decrement remainder_ns in that case.
Expand Down
16 changes: 8 additions & 8 deletions test/codesize/test_codesize_minimal_pthreads.json
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Original file line number Diff line number Diff line change
@@ -1,14 +1,14 @@
{
"a.out.js": 7363,
"a.out.js.gz": 3604,
"a.out.nodebug.wasm": 19244,
"a.out.nodebug.wasm.gz": 8919,
"total": 26607,
"total_gz": 12523,
"a.out.nodebug.wasm": 19046,
"a.out.nodebug.wasm.gz": 8822,
"total": 26409,
"total_gz": 12426,
"sent": [
"a (memory)",
"b (emscripten_get_now)",
"c (exit)",
"b (exit)",
"c (emscripten_get_now)",
"d (_emscripten_thread_set_strongref)",
"e (_emscripten_receive_on_main_thread_js)",
"f (emscripten_runtime_keepalive_check)",
Expand All @@ -23,8 +23,8 @@
],
"imports": [
"a (memory)",
"b (emscripten_get_now)",
"c (exit)",
"b (exit)",
"c (emscripten_get_now)",
"d (_emscripten_thread_set_strongref)",
"e (_emscripten_receive_on_main_thread_js)",
"f (emscripten_runtime_keepalive_check)",
Expand Down
16 changes: 8 additions & 8 deletions test/codesize/test_codesize_minimal_pthreads_memgrowth.json
View file
Open in desktop
Original file line number Diff line number Diff line change
@@ -1,14 +1,14 @@
{
"a.out.js": 7765,
"a.out.js.gz": 3810,
"a.out.nodebug.wasm": 19245,
"a.out.nodebug.wasm.gz": 8920,
"total": 27010,
"total_gz": 12730,
"a.out.nodebug.wasm": 19047,
"a.out.nodebug.wasm.gz": 8823,
"total": 26812,
"total_gz": 12633,
"sent": [
"a (memory)",
"b (emscripten_get_now)",
"c (exit)",
"b (exit)",
"c (emscripten_get_now)",
"d (_emscripten_thread_set_strongref)",
"e (_emscripten_receive_on_main_thread_js)",
"f (emscripten_runtime_keepalive_check)",
Expand All @@ -23,8 +23,8 @@
],
"imports": [
"a (memory)",
"b (emscripten_get_now)",
"c (exit)",
"b (exit)",
"c (emscripten_get_now)",
"d (_emscripten_thread_set_strongref)",
"e (_emscripten_receive_on_main_thread_js)",
"f (emscripten_runtime_keepalive_check)",
Expand Down
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