Simplify WaiterNode, make it private. Improve UEvent autoclear logic.

nx/include/switch/kernel/wait.h

@@ -13,11 +13,6 @@
 typedef struct UEvent UEvent;
 typedef struct UTimer UTimer;
 
-typedef enum {
-    WaiterNodeType_Event,
-    WaiterNodeType_Timer,
-} WaiterNodeType;
-
 typedef struct Waitable Waitable;
 typedef struct WaitableNode WaitableNode;
 
@@ -26,19 +21,6 @@ struct WaitableNode {
     WaitableNode* next;
 };
 
-typedef struct {
-    WaitableNode node;
-    WaiterNodeType type;
-    Handle thread;
-    union {
-        Waitable* parent;
-        UEvent* parent_event;
-        UTimer* parent_timer;
-    };
-    s32 idx;
-    s32* idx_out;
-} WaiterNode;
-
 struct Waitable {
     WaitableNode list;
     Mutex mutex;

nx/source/kernel/uevent.c

@@ -2,7 +2,6 @@
 #include "kernel/svc.h"
 #include "kernel/mutex.h"
 #include "kernel/uevent.h"
-#include "wait.h"
 #include "uevent.h"
 
 void ueventCreate(UEvent* e, bool auto_clear)
@@ -28,28 +27,31 @@ void ueventSignal(UEvent* e)
     mutexUnlock(&e->waitable.mutex);
 }
 
-void _ueventTryAutoClear(UEvent* e)
+Result _ueventTryAutoClear(UEvent* e)
 {
+    Result rc = 0;
     mutexLock(&e->waitable.mutex);
-    if (e->auto_clear)
+    if (e->auto_clear) {
-        e->signal = false;
+        if (e->signal)
+            e->signal = 0;
+        else
+            rc = KERNELRESULT(Cancelled);
+    }
     mutexUnlock(&e->waitable.mutex);
+    return rc;
 }
 
 bool _ueventAddListener(UEvent* e, WaiterNode* w, s32 idx, s32* idx_out, Handle thread)
 {
     mutexLock(&e->waitable.mutex);
 
-    bool signalled = e->signal;
+    bool can_add = !e->signal;
 
-    if (signalled) {
+    if (can_add)
-        if (e->auto_clear)
+        _waiterNodeAdd(w, &e->waitable, thread, idx, idx_out);
-            e->signal = false;
+    else if (e->auto_clear)
-    } else {
+        e->signal = false;
-        _waiterNodeCreate(w, WaiterNodeType_Event, &e->waitable, thread, idx, idx_out);
-        _waiterNodeAddToWaitable(w, &e->waitable);
-    }
 
     mutexUnlock(&e->waitable.mutex);
-    return !signalled;
+    return can_add;
 }

nx/source/kernel/uevent.h

@@ -1,6 +1,7 @@
 // Copyright 2018 plutoo
 #pragma once
 #include "kernel/uevent.h"
+#include "wait.h"
 
-void _ueventTryAutoClear(UEvent* e);
+Result _ueventTryAutoClear(UEvent* e);
 bool _ueventAddListener(UEvent* e, WaiterNode* w, s32 idx, s32* idx_out, Handle thread);

nx/source/kernel/utimer.c

@@ -2,7 +2,6 @@
 #include "kernel/svc.h"
 #include "kernel/utimer.h"
 #include "arm/counter.h"
-#include "utimer.h"
 #include "wait.h"
 
 #define STOPPED 0
@@ -77,9 +76,7 @@ u64 _utimerGetNextTick(UTimer* t)
 
 void _utimerAddListener(UTimer* t, WaiterNode* w, s32 idx, s32* idx_out, Handle thread)
 {
-    _waiterNodeCreate(w, WaiterNodeType_Timer, &t->waitable, thread, idx, idx_out);
-
     mutexLock(&t->waitable.mutex);
-    _waiterNodeAddToWaitable(w, &t->waitable);
+    _waiterNodeAdd(w, &t->waitable, thread, idx, idx_out);
     mutexUnlock(&t->waitable.mutex);
 }

nx/source/kernel/utimer.h

@@ -1,6 +1,7 @@
 // Copyright 2018 plutoo
 #pragma once
 #include "kernel/utimer.h"
+#include "wait.h"
 
 void _utimerRecalculate(UTimer* t, u64 old_tick);
 u64  _utimerGetNextTick(UTimer* t);

nx/source/kernel/wait.c

@@ -114,7 +114,7 @@ static Result waitImpl(s32* idx_out, Waiter* objects, size_t num_objects, u64 ti
         *idx_out = end_tick_idx;
         rc = 0;
     } else if (rc == KERNELRESULT(Cancelled)) {
-        // If no listener filled in its own index, we return the interrupt error back to caller.
+        // If no listener filled in its own index, we return the cancelled error back to caller.
         // This only happens if user for some reason manually does a svcCancelSynchronization.
         // Check just in case.
         if (triggered_idx == -1)
@@ -122,15 +122,21 @@ static Result waitImpl(s32* idx_out, Waiter* objects, size_t num_objects, u64 ti
 
         // An event was signalled, or a timer was updated.
         // So.. which is it?
-        switch (waiters[triggered_idx].type) {
+        switch (objects[triggered_idx].type) {
-            case WaiterNodeType_Event:
+            default:
-                _ueventTryAutoClear(waiters[triggered_idx].parent_event);
-
-                *idx_out = triggered_idx;
-                rc = 0;
                 break;
 
-            case WaiterNodeType_Timer:
+            case WaiterType_UEvent:
+                // Try to auto-clear the event. If auto-clear is enabled but
+                // the event is not signalled, that means the state of the
+                // event has changed and thus we need to retry the wait.
+                rc = _ueventTryAutoClear(objects[triggered_idx].event);
+                if (R_SUCCEEDED(rc))
+                    *idx_out = triggered_idx;
+                break;
+
+            case WaiterType_UTimer:
+                // Timer state changed, so we need to retry the wait.
                 rc = KERNELRESULT(Cancelled);
                 break;
         }
@@ -140,7 +146,7 @@ clean_up:
     // Remove listeners.
     for (i = 0; i < num_objects; i ++)
         if (waiters_added & (1ULL << i))
-            _waiterNodeFree(&waiters[i]);
+            _waiterNodeRemove(&waiters[i]);
 
     return rc;
 }

nx/source/kernel/wait.h

@@ -3,6 +3,16 @@
 #include "kernel/mutex.h"
 #include "kernel/wait.h"
 
+typedef struct WaiterNode WaiterNode;
+
+struct WaiterNode {
+    WaitableNode node;
+    Waitable* parent;
+    Handle thread;
+    s32* idx_out;
+    s32 idx;
+};
+
 static inline void _waitableInitialize(Waitable* ww)
 {
     mutexInit(&ww->mutex);
@@ -30,25 +40,23 @@ static inline void _waitableSignalAllListeners(Waitable* ww)
     }
 }
 
-static inline void _waiterNodeCreate(
+static inline void _waiterNodeAdd(
-    WaiterNode* w, WaiterNodeType type, Waitable* parent, Handle thread,
+    WaiterNode* w, Waitable* parent, Handle thread,
     s32 idx, s32* idx_out)
 {
-    w->type = type;
+    // Initialize WaiterNode fields
     w->parent = parent;
     w->thread = thread;
     w->idx = idx;
     w->idx_out = idx_out;
+
+    // Add WaiterNode to the parent's linked list
+    w->node.next = parent->list.next;
+    parent->list.next = &w->node;
+    w->node.prev = &parent->list;
 }
 
-static inline void _waiterNodeAddToWaitable(WaiterNode* w, Waitable* ww)
+static inline void _waiterNodeRemove(WaiterNode* w)
-{
-    w->node.next = ww->list.next;
-    ww->list.next = &w->node;
-    w->node.prev = &ww->list;
-}
-
-static inline void _waiterNodeFree(WaiterNode* w)
 {
     mutexLock(&w->parent->mutex);
     w->node.prev->next = w->node.next;