loop: add some comment on reset functions (#305)

* loop: add some comment on reset functions

* loop: inline cancelAll and remove useless resetEvents

* loop: reset events before waiting during deinit

Author: krichprollsch

src/loop.zig

@@ -33,8 +33,12 @@ const log = std.log.scoped(.loop);
 pub const SingleThreaded = struct {
     alloc: std.mem.Allocator, // TODO: unmanaged version ?
     io: IO,
+
+    // both events_nb are used to track how many callbacks are to be called.
+    // We use these counters to wait until all the events are finished.
     js_events_nb: usize,
     zig_events_nb: usize,
+
     cbk_error: bool = false,
 
     // js_ctx_id is incremented each time the loop is reset for JS.
@@ -79,6 +83,12 @@ pub const SingleThreaded = struct {
     }
 
     pub fn deinit(self: *Self) void {
+        // first disable callbacks for existing events.
+        // We don't want a callback re-create a setTimeout, it could create an
+        // infinite loop on wait for events.
+        self.resetJS();
+        self.resetZig();
+
         // run tail events. We do run the tail events to ensure all the
         // contexts are correcly free.
         while (self.eventsNb(.js) > 0 or self.eventsNb(.zig) > 0) {
@@ -88,7 +98,7 @@ pub const SingleThreaded = struct {
             };
         }
         if (comptime CANCEL_SUPPORTED) {
-            self.cancelAll();
+            self.io.cancel_all();
         }
         self.io.deinit();
         self.cancel_pool.deinit();
@@ -138,9 +148,6 @@ pub const SingleThreaded = struct {
     fn eventsNb(self: *Self, comptime event: Event) usize {
         return @atomicLoad(usize, self.eventsPtr(event), .seq_cst);
     }
-    fn resetEvents(self: *Self, comptime event: Event) void {
-        @atomicStore(usize, self.eventsPtr(event), 0, .unordered);
-    }
 
     // JS callbacks APIs
     // -----------------
@@ -284,19 +291,17 @@ pub const SingleThreaded = struct {
         self.io.cancel_one(*ContextCancel, ctx, cancelCallback, completion, comp_cancel);
     }
 
-    fn cancelAll(self: *Self) void {
-        self.resetEvents(.js);
-        self.resetEvents(.zig);
-        self.io.cancel_all();
-    }
-
     // Reset all existing JS callbacks.
+    // The existing events will happen and their memory will be cleanup but the
+    // corresponding callbacks will not be called.
     pub fn resetJS(self: *Self) void {
         self.js_ctx_id += 1;
         self.cancelled.clearRetainingCapacity();
     }
 
     // Reset all existing Zig callbacks.
+    // The existing events will happen and their memory will be cleanup but the
+    // corresponding callbacks will not be called.
     pub fn resetZig(self: *Self) void {
         self.zig_ctx_id += 1;
     }