simplify the fix

src/Watcher.cc

@@ -66,6 +66,11 @@ void Watcher::notify() {
   mCond.notify_all();
 
   if (mCallbacks.size() > 0 && mEvents.size() > 0) {
+    // We must release our lock before calling into the debouncer
+    // to avoid a deadlock: the debouncer thread itself will require 
+    // our lock from its thread when calling into `triggerCallbacks` 
+    // while holding its own debouncer lock.
+    lk.unlock();
     mDebounce->trigger();
   }
 }
@@ -113,7 +118,7 @@ void Watcher::notifyError(std::exception &err) {
 
 // This function is called from the debounce thread.
 void Watcher::triggerCallbacks() {
-  std::unique_lock<std::mutex> lk(mCallbackEventsMutex);
+  std::unique_lock<std::mutex> lk(mMutex);
   if (mCallbacks.size() > 0 && mEvents.size() > 0) {
     auto events = mEvents.getEvents();
     mEvents.clear();

src/Watcher.hh

@@ -54,7 +54,6 @@ struct Watcher {
 
 private:
   std::mutex mMutex;
-  std::mutex mCallbackEventsMutex;
   std::condition_variable mCond;
   std::vector<Callback> mCallbacks;
   std::shared_ptr<Debounce> mDebounce;