File size: 2,615 Bytes
00df61d | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 | /*
* Copyright 2021 The Emscripten Authors. All rights reserved.
* Emscripten is available under two separate licenses, the MIT license and the
* University of Illinois/NCSA Open Source License. Both these licenses can be
* found in the LICENSE file.
*/
#include "atomic.h"
#include "pthread_impl.h"
#include <assert.h>
#include <errno.h>
#include <limits.h>
#include <stdatomic.h>
#include <emscripten/threading.h>
// Stores the memory address that the main thread is waiting on, if any. If
// the main thread is waiting, we wake it up before waking up any workers.
void* _emscripten_main_thread_futex;
// Returns the number of threads (>= 0) woken up, or the value -EINVAL on error.
// Pass count == INT_MAX to wake up all threads.
int emscripten_futex_wake(volatile void *addr, int count) {
if (!addr || (((intptr_t)addr) & 3) != 0 || count < 0) {
return -EINVAL;
}
if (count == 0) {
return 0;
}
// See if main thread is waiting on this address? If so, wake it up by
// resetting its wake location to zero. Note that this is not a fair
// procedure, since we always wake main thread first before any workers, so
// this scheme does not adhere to real queue-based waiting.
int main_thread_woken = 0;
if (a_cas_p(&_emscripten_main_thread_futex, (void*)addr, 0) == addr) {
// The main browser thread must never try to wake itself up!
assert(!emscripten_is_main_browser_thread());
if (count != INT_MAX) {
--count;
main_thread_woken = 1;
if (count <= 0) {
return 1;
}
}
}
// Wake any workers waiting on this address.
int ret = __builtin_wasm_memory_atomic_notify((int*)addr, count);
assert(ret >= 0);
return ret + main_thread_woken;
}
void _emscripten_thread_notify(pthread_t target) {
DBG("_emscripten_thread_notify %p", target);
uintptr_t wait_addr = atomic_fetch_or(&target->wait_addr, NOTIFY_BIT);
if (wait_addr == 0 || (wait_addr & NOTIFY_BIT)) {
// Either the thread wasn't waiting (In this case it will see NOTIFY_BIT and
// return early once it enters its next `emscripten_futex_wait`), or someone
// else is already in the process of notifying it.
return;
}
// We set the NOTIFY_BIT bit and are responsible for waking the target.
// The target is currently waiting on `wait_addr`.
while (target->wait_addr == (wait_addr | NOTIFY_BIT)) {
emscripten_futex_wake((void*)wait_addr, INT_MAX);
// TODO: Can we put some kind of yield instruction here? For example,
// it we ever support an `atomics.pause` Wasm instruction this would be a
// good place for it.
}
}
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