revert wake change

core/nbio/impl_windows.odin

@@ -25,6 +25,11 @@ _Event_Loop :: struct {
 	thread:        win.HANDLE,
 	completed:     queue.Queue(^Operation),
 	completed_oob: Multi_Producer_Single_Consumer,
+	state: enum {
+		Working,
+		Waking,
+		Sleeping,
+	},
 }
 
 @(private="package")
@@ -163,8 +168,11 @@ __tick :: proc(l: ^Event_Loop, timeout: time.Duration) -> (err: General_Error) {
 	actual_timeout := compute_timeout(l, timeout, next_timeout)
 
 	if actual_timeout > 0 {
-		// Work may have been queued after the drain at the top of this tick,
-		// so check the queues once more before blocking.
+		sync.atomic_store_explicit(&l.state, .Sleeping, .Release)
+
+		// There could be a race condition where we go sleeping at the same time as things get queued
+		// and a wakeup isn't done because the state is not .Sleeping yet.
+		// So after sleeping we first check our queues.
 		for {
 			op := (^Operation)(mpsc_dequeue(&l.queue))
 			if op == nil { break }
@@ -196,6 +204,8 @@ __tick :: proc(l: ^Event_Loop, timeout: time.Duration) -> (err: General_Error) {
 			}
 		}
 
+		sync.atomic_store_explicit(&l.state, .Working, .Relaxed)
+
 		if actual_timeout > 0 {
 			// We may have just waited some time, lets update the current time.
 			l.now = time.now()
@@ -768,10 +778,10 @@ _associate_socket :: proc(socket: Any_Socket, l: ^Event_Loop) -> Association_Err
 
 @(private="package")
 _wake_up :: proc(l: ^Event_Loop) {
-	// Unconditional: an APC queued before the loop enters its alertable wait stays
-	// pending and is delivered as soon as that wait begins. Queueing it only once the
-	// loop is already asleep drops every wake sent while it is still awake.
-	win.QueueUserAPC(proc "system" (Parameter: win.ULONG_PTR) {}, l.thread, 0)
+	_, exchanged := sync.atomic_compare_exchange_strong(&l.state, .Sleeping, .Waking)
+	if exchanged {
+		win.QueueUserAPC(proc "system" (Parameter: win.ULONG_PTR) {}, l.thread, 0)
+	}
 }
 
 @(private="package")