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Only use futex_wait_busy on the main browser thread #18402

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Merged
sbc100 merged 1 commit into from
Dec 26, 2022
Merged

Only use futex_wait_busy on the main browser thread #18402

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21 changes: 14 additions & 7 deletions system/lib/pthread/emscripten_futex_wait.c
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Original file line number Diff line number Diff line change
Expand Up @@ -17,7 +17,9 @@ extern void* _emscripten_main_thread_futex;

int _emscripten_thread_supports_atomics_wait(void);

static int futex_wait_busy(volatile void *addr, uint32_t val, double timeout) {
static int futex_wait_main_browser_thread(volatile void* addr,
uint32_t val,
double timeout) {
// Atomics.wait is not available in the main browser thread, so simulate it
// via busy spinning.
double now = emscripten_get_now();
Expand Down Expand Up @@ -119,13 +121,18 @@ int emscripten_futex_wait(volatile void *addr, uint32_t val, double max_wait_ms)
int ret;
emscripten_conditional_set_current_thread_status(EM_THREAD_STATUS_RUNNING, EM_THREAD_STATUS_WAITFUTEX);

// For threads that cannot block (i.e. the main browser thread) we can't use
// __builtin_wasm_memory_atomic_wait32 so we call out the JS function that
// will busy wait.
// For the main browser thread we can't use
// __builtin_wasm_memory_atomic_wait32 so we have busy wait instead.
if (!_emscripten_thread_supports_atomics_wait()) {
ret = futex_wait_busy(addr, val, max_wait_ms);
emscripten_conditional_set_current_thread_status(EM_THREAD_STATUS_WAITFUTEX, EM_THREAD_STATUS_RUNNING);
return ret;
if (emscripten_is_main_browser_thread()) {
ret = futex_wait_main_browser_thread(addr, val, max_wait_ms);
emscripten_conditional_set_current_thread_status(EM_THREAD_STATUS_WAITFUTEX, EM_THREAD_STATUS_RUNNING);
return ret;
} else {
// TODO: handle non-main threads that also don't support `atomic.wait`.
// For example AudioWorklet.
assert(0);
}
}

// -1 (or any negative number) means wait indefinitely.
Expand Down