system/lib/pthread/emscripten_yield.c

#include <stdbool.h>
#include <sched.h>
#include <threads.h>
#include "syscall.h"

#include <emscripten/threading.h>

static _Atomic bool thread_crashed = false;

void _emscripten_thread_crashed() {
  thread_crashed = true;
}

static void dummy()
{
}

weak_alias(dummy, _emscripten_thread_sync_code);

/*
 * Called whenever a thread performs a blocking action (or calls sched_yield).
 * This function takes care of running the event queue and other housekeeping
 * tasks.
 */
void _emscripten_yield() {
  int is_runtime_thread = emscripten_is_main_runtime_thread();

  // When a secondary thread crashes, we need to be able to interrupt the main
  // thread even if it's in a blocking/looping on a mutex.  We want to avoid
  // using the normal proxying mechanism to send this message since it can
  // allocate (or otherwise itself crash) so use a low level atomic primitive
  // for this signal.
  if (is_runtime_thread) {
    if (thread_crashed) {
      // Return the event loop so we can handle the message from the crashed
      // thread.
      emscripten_unwind_to_js_event_loop();
    }

    // Assist other threads by executing proxied operations that are effectively
    // singlethreaded.
    emscripten_main_thread_process_queued_calls();
  }

  _emscripten_thread_sync_code();
}