Handle thread crash/abort even when main thread is blocking (busy-wai…

…ting). NFC

Previously if a thread crashed when the main thread was blocked on
something (such as pthread_join) it would never get the `onerror`
message because it would never return the event loop.

emcc.py

@@ -2052,6 +2052,7 @@ def default_setting(name, new_default):
     worker_imports = [
       '__emscripten_thread_init',
       '__emscripten_thread_exit',
+      '__emscripten_thread_crashed',
       '_emscripten_tls_init',
       '_emscripten_current_thread_process_queued_calls',
       '_pthread_self',

src/worker.js

@@ -290,6 +290,9 @@ self.onmessage = (e) => {
       err(e.data);
     }
   } catch(ex) {
+    if (Module['__emscripten_thread_crashed']) {
+      Module['__emscripten_thread_crashed']();
+    }
     err('worker.js onmessage() captured an uncaught exception: ' + ex);
     if (ex && ex.stack) err(ex.stack);
     throw ex;

system/lib/pthread/emscripten_futex_wait.c

@@ -8,6 +8,8 @@
 #include <errno.h>
 #include <math.h>
 #include <emscripten/threading.h>
+#include <stdbool.h>
+#include <stdlib.h>
 #include "atomic.h"
 #include "threading_internal.h"
 
@@ -106,11 +108,24 @@ static int futex_wait_busy(volatile void *addr, uint32_t val, double timeout) {
   return 0;
 }
 
+static _Atomic bool thread_crashed = false;
+
+void _emscripten_thread_crashed() {
+  thread_crashed = true;
+}
+
 int emscripten_futex_wait(volatile void *addr, uint32_t val, double max_wait_ms) {
   if ((((intptr_t)addr)&3) != 0) {
     return -EINVAL;
   }
 
+  // When a secondary thread crashes we need to be able to inturrupt the main
+  // thread is its in a busy loop.  We can't use the normal proxying mechanism
+  // since it could allocate or itself crash so use a low level atomic primitive
+  // for this signal.
+  if (emscripten_is_main_runtime_thread() && thread_crashed)
+    abort();
+
   int ret;
   emscripten_conditional_set_current_thread_status(EM_THREAD_STATUS_RUNNING, EM_THREAD_STATUS_WAITFUTEX);