[gnome-shell] signalTracker: Remove SignalTracker after its last signal got untracked

[Marge Bot <marge-bot src gnome org>]

commit 91ce5ca960879dbe810cde43265d00b5c6446a1a
Author: Sebastian Keller <skeller gnome org>
Date:   Mon Aug 29 00:03:50 2022 +0200

    signalTracker: Remove SignalTracker after its last signal got untracked
    
    The object the SignalTracker belongs to is stored in a map managed by
    the SignalManager which keeps a reference to that object. This map is
    never destroyed nor is any entry ever removed. This leads to all objects
    that ever had SignalTrackers used on them being kept alive even after
    all references outside of the SignalTracker are long gone. This then
    also extends to other objects which are leaked indirectly through
    reference chains from these objects.
    
    And if some of those objects are GObjects, this will prevent them from
    being finalized, leaking further resources. A StWidget for example will
    not release its shadow textures.
    
    Fix this by destroying the SignalTracker and removing it from the
    SignalManager once the last signal it was tracking has been untracked.
    
    A WeakMap could have been used as well, but we need the Map to be
    iterable in some of the following changes.
    
    Closes: https://gitlab.gnome.org/GNOME/gnome-shell/-/issues/5807
    Closes: https://gitlab.gnome.org/GNOME/gnome-shell/-/issues/5796
    Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2466>

 js/misc/signalTracker.js | 28 ++++++++++++++++++++++------
 1 file changed, 22 insertions(+), 6 deletions(-)
---
diff --git a/js/misc/signalTracker.js b/js/misc/signalTracker.js
index c72abd265e..3b71fbc592 100644
--- a/js/misc/signalTracker.js
+++ b/js/misc/signalTracker.js
@@ -65,6 +65,14 @@ class SignalManager {
     maybeGetSignalTracker(obj) {
         return this._signalTrackers.get(obj) ?? null;
     }
+
+    /*
+     * @param {Object} obj - object to remove signal tracker for
+     * @returns {void}
+     */
+    removeSignalTracker(obj) {
+        this._signalTrackers.delete(obj);
+    }
 }
 
 class SignalTracker {
@@ -124,6 +132,16 @@ class SignalTracker {
         this._disconnectSignalForProto(this._getObjectProto(obj), obj, id);
     }
 
+    _removeTracker() {
+        if (this._ownerDestroyId)
+            this._disconnectSignal(this._owner, this._ownerDestroyId);
+
+        SignalManager.getDefault().removeSignalTracker(this._owner);
+
+        delete this._ownerDestroyId;
+        delete this._owner;
+    }
+
     /**
      * @param {Object} obj - tracked object
      * @param {...number} handlerIds - tracked handler IDs
@@ -149,6 +167,9 @@ class SignalTracker {
             this._disconnectSignalForProto(ownerProto, this._owner, id));
         if (destroyId)
             this._disconnectSignal(obj, destroyId);
+
+        if (this._map.size === 0)
+            this._removeTracker();
     }
 
     /**
@@ -163,12 +184,7 @@ class SignalTracker {
      */
     destroy() {
         this.clear();
-
-        if (this._ownerDestroyId)
-            this._disconnectSignal(this._owner, this._ownerDestroyId);
-
-        delete this._ownerDestroyId;
-        delete this._owner;
+        this._removeTracker();
     }
 }