event loop: attempt to handle different types of events with more fairness

1 files changed, 46 insertions, 32 deletions

diff --git a/quickjs/quickjs-libc.c b/quickjs/quickjs-libc.c
index 96b419b..544719a 100644
--- a/quickjs/quickjs-libc.c
+++ b/quickjs/quickjs-libc.c
@@ -179,6 +179,9 @@ typedef struct JSThreadState {
 
     int is_worker_thread;
 
+    // used to provided fairer scheduling of event reactions
+    unsigned int poll_iteration_count;
+
     struct list_head http_requests;
 
 #ifndef NO_HTTP
@@ -2949,46 +2952,57 @@ static int js_os_poll(JSContext *ctx)
 
     ret = select(fd_max + 1, &rfds, &wfds, NULL, tvp);
     if (ret > 0) {
-        list_for_each(el, &ts->os_rw_handlers) {
-            rh = list_entry(el, JSOSRWHandler, link);
-            if (!JS_IsNull(rh->rw_func[0]) &&
-                FD_ISSET(rh->fd, &rfds)) {
-                call_handler(ctx, rh->rw_func[0]);
-                /* must stop because the list may have been modified */
-                goto done;
-            }
-            if (!JS_IsNull(rh->rw_func[1]) &&
-                FD_ISSET(rh->fd, &wfds)) {
-                call_handler(ctx, rh->rw_func[1]);
-                /* must stop because the list may have been modified */
-                goto done;
+        // Start with a different event type on every iteration
+        // for fairness.
+        switch (ts->poll_iteration_count % 4) {
+        case 0:
+           list_for_each(el, &ts->os_rw_handlers) {
+               rh = list_entry(el, JSOSRWHandler, link);
+               if (!JS_IsNull(rh->rw_func[0]) &&
+                   FD_ISSET(rh->fd, &rfds)) {
+                   call_handler(ctx, rh->rw_func[0]);
+                   /* must stop because the list may have been modified */
+                   goto done;
+               }
+               if (!JS_IsNull(rh->rw_func[1]) &&
+                   FD_ISSET(rh->fd, &wfds)) {
+                   call_handler(ctx, rh->rw_func[1]);
+                   /* must stop because the list may have been modified */
+                   goto done;
+               }
+           }
+           /* fallthrough */
+        case 1:
+            list_for_each(el, &ts->port_list) {
+                JSWorkerMessageHandler *port = list_entry(el, JSWorkerMessageHandler, link);
+                if (!JS_IsNull(port->on_message_func)) {
+                    JSWorkerMessagePipe *ps = port->recv_pipe;
+                    if (FD_ISSET(ps->read_fd, &rfds)) {
+                        if (handle_posted_message(rt, ctx, port))
+                            goto done;
+                    }
+                }
             }
-        }
-
-        list_for_each(el, &ts->port_list) {
-            JSWorkerMessageHandler *port = list_entry(el, JSWorkerMessageHandler, link);
-            if (!JS_IsNull(port->on_message_func)) {
-                JSWorkerMessagePipe *ps = port->recv_pipe;
-                if (FD_ISSET(ps->read_fd, &rfds)) {
-                    if (handle_posted_message(rt, ctx, port))
-                        goto done;
+           /* fallthrough */
+        case 2:
+            if (FD_ISSET(ts->host_pipe->read_fd, &rfds)) {
+                if (handle_host_message(rt, ctx)) {
+                    goto done;
                 }
             }
-        }
-
-        if (FD_ISSET(ts->host_pipe->read_fd, &rfds)) {
-            if (handle_host_message(rt, ctx)) {
-                goto done;
+           /* fallthrough */
+        case 3:
+            if (FD_ISSET(ts->http_pipe->read_fd, &rfds)) {
+                if (handle_http_message(rt, ctx)) {
+                    goto done;
+                }
             }
+           /* fallthrough */
         }
 
-        if (FD_ISSET(ts->http_pipe->read_fd, &rfds)) {
-            if (handle_http_message(rt, ctx)) {
-                goto done;
-            }
-        }
     }
     done:
+    ts->poll_iteration_count++;
     return 0;
 }
 #endif /* !_WIN32 */