dirmonitor: use pipes on fsevents (#1274)

As suggested by Guldoman this change introduces the usage
of pipes to allow blocking the get changes call until any
file system changes are received, which now properly reduces
the cpu usage on idle to 0%.

This change better fixes #1237

src/api/dirmonitor/fsevents.c

@@ -6,6 +6,7 @@ struct dirmonitor_internal {
   char** changes;
   size_t count;
   FSEventStreamRef stream;
+  int fds[2];
 };
 
 CFRunLoopRef main_run_loop;
@@ -39,6 +40,9 @@ static void stop_monitor_stream(struct dirmonitor_internal* monitor) {
     monitor->stream = NULL;
 
     SDL_LockMutex(monitor->lock);
+    write(monitor->fds[1], "", 1);
+    close(monitor->fds[0]);
+    close(monitor->fds[1]);
     if (monitor->count > 0) {
       for (size_t i = 0; i<monitor->count; i++) {
         free(monitor->changes[i]);
@@ -92,6 +96,9 @@ static void stream_callback(
     strcpy(monitor->changes[idx], path_list[pidx]);
   }
   monitor->count = total;
+
+  if (total > 0)
+    write(monitor->fds[1], "", 1);
   SDL_UnlockMutex(monitor->lock);
 }
 
@@ -101,16 +108,14 @@ int get_changes_dirmonitor(
   char* buffer,
   int buffer_size
 ) {
-  FSEventStreamFlushSync(monitor->stream);
+  char response[1];
+  read(monitor->fds[0], response, 1);
 
   size_t results = 0;
   SDL_LockMutex(monitor->lock);
   results = monitor->count;
   SDL_UnlockMutex(monitor->lock);
 
-  if (monitor->count <= 0)
-    SDL_Delay(100);
-
   return results;
 }
 
@@ -141,6 +146,7 @@ int add_dirmonitor(struct dirmonitor_internal* monitor, const char* path) {
   stop_monitor_stream(monitor);
 
   monitor->lock = SDL_CreateMutex();
+  pipe(monitor->fds);
 
   FSEventStreamContext context = {
     .info = monitor,
@@ -160,7 +166,7 @@ int add_dirmonitor(struct dirmonitor_internal* monitor, const char* path) {
     &context,
     CFArrayCreate(NULL, (const void **)&paths, 1, NULL),
     kFSEventStreamEventIdSinceNow,
-    10000,
+    0,
     kFSEventStreamCreateFlagNone
       | kFSEventStreamCreateFlagWatchRoot
       | kFSEventStreamCreateFlagFileEvents