Fix handling of image cache refcounts. (Bug#20802)

This backports Eli Zaretskii's solution of this problem for W32
to X and NS.

* src/nsfns.m (image_cache_refcount): Define unconditionally.
(unwind_create_frame): If the image cache's reference count
hasn't been updated yet, do that now.
(Fx_create_frame): Set image_cache_refcount unconditionally.
* src/xfns.c (image_cache_refcount): Define unconditionally.
(unwind_create_frame): If the image cache's reference count
hasn't been updated yet, do that now.
(Fx_create_frame, x_create_tip_frame): Set image_cache_refcount
unconditionally.
* src/w32fns.c (image_cache_refcount): Make it a ptrdiff_t as on
X and NS.

3 files changed, 27 insertions, 8 deletions

diff --git a/src/nsfns.m b/src/nsfns.m
index 6a2e2ff14a4..286445c0030 100644
--- a/src/nsfns.m
+++ b/src/nsfns.m
@@ -70,9 +70,7 @@ Lisp_Object Fx_open_connection (Lisp_Object, Lisp_Object, Lisp_Object);
 static Lisp_Object as_script, *as_result;
 static int as_status;
 
-#ifdef GLYPH_DEBUG
 static ptrdiff_t image_cache_refcount;
-#endif
 
 
 /* ==========================================================================
@@ -1005,6 +1003,17 @@ unwind_create_frame (Lisp_Object frame)
       struct ns_display_info *dpyinfo = FRAME_DISPLAY_INFO (f);
 #endif
 
+      /* If the frame's image cache refcount is still the same as our
+         private shadow variable, it means we are unwinding a frame
+         for which we didn't yet call init_frame_faces, where the
+         refcount is incremented.  Therefore, we increment it here, so
+         that free_frame_faces, called in x_free_frame_resources
+         below, will not mistakenly decrement the counter that was not
+         incremented yet to account for this new frame.  */
+      if (FRAME_IMAGE_CACHE (f) != NULL
+          && FRAME_IMAGE_CACHE (f)->refcount == image_cache_refcount)
+        FRAME_IMAGE_CACHE (f)->refcount++;
+
       x_free_frame_resources (f);
       free_glyphs (f);
 
@@ -1241,10 +1250,8 @@ This function is an internal primitive--use `make-frame' instead.  */)
   x_default_parameter (f, parms, Qright_fringe, Qnil,
                        "rightFringe", "RightFringe", RES_TYPE_NUMBER);
 
-#ifdef GLYPH_DEBUG
   image_cache_refcount =
     FRAME_IMAGE_CACHE (f) ? FRAME_IMAGE_CACHE (f)->refcount : 0;
-#endif
 
   init_frame_faces (f);
 
diff --git a/src/w32fns.c b/src/w32fns.c
index c247a9b3b3a..5f40729011e 100644
--- a/src/w32fns.c
+++ b/src/w32fns.c
@@ -204,7 +204,8 @@ unsigned int msh_mousewheel = 0;
 static unsigned menu_free_timer = 0;
 
 #ifdef GLYPH_DEBUG
-static int image_cache_refcount, dpyinfo_refcount;
+static ptrdiff_t image_cache_refcount;
+static int dpyinfo_refcount;
 #endif
 
 static HWND w32_visible_system_caret_hwnd;
diff --git a/src/xfns.c b/src/xfns.c
index 634881d0a66..d066043ae5e 100644
--- a/src/xfns.c
+++ b/src/xfns.c
@@ -120,8 +120,8 @@ extern LWLIB_ID widget_id_tick;
 
 #define MAXREQUEST(dpy) (XMaxRequestSize (dpy))
 
-#ifdef GLYPH_DEBUG
 static ptrdiff_t image_cache_refcount;
+#ifdef GLYPH_DEBUG
 static int dpyinfo_refcount;
 #endif
 
@@ -2828,6 +2828,17 @@ unwind_create_frame (Lisp_Object frame)
       struct x_display_info *dpyinfo = FRAME_DISPLAY_INFO (f);
 #endif
 
+      /* If the frame's image cache refcount is still the same as our
+         private shadow variable, it means we are unwinding a frame
+         for which we didn't yet call init_frame_faces, where the
+         refcount is incremented.  Therefore, we increment it here, so
+         that free_frame_faces, called in x_free_frame_resources
+         below, will not mistakenly decrement the counter that was not
+         incremented yet to account for this new frame.  */
+      if (FRAME_IMAGE_CACHE (f) != NULL
+          && FRAME_IMAGE_CACHE (f)->refcount == image_cache_refcount)
+        FRAME_IMAGE_CACHE (f)->refcount++;
+
       x_free_frame_resources (f);
       free_glyphs (f);
 
@@ -3205,9 +3216,9 @@ This function is an internal primitive--use `make-frame' instead.  */)
                                         "scrollBarBackground",
                                         "ScrollBarBackground", false);
 
-#ifdef GLYPH_DEBUG
   image_cache_refcount =
     FRAME_IMAGE_CACHE (f) ? FRAME_IMAGE_CACHE (f)->refcount : 0;
+#ifdef GLYPH_DEBUG
   dpyinfo_refcount = dpyinfo->reference_count;
 #endif /* GLYPH_DEBUG */
 
@@ -5178,9 +5189,9 @@ x_create_tip_frame (struct x_display_info *dpyinfo,
   x_default_parameter (f, parms, Qborder_color, build_string ("black"),
                        "borderColor", "BorderColor", RES_TYPE_STRING);
 
-#ifdef GLYPH_DEBUG
   image_cache_refcount =
     FRAME_IMAGE_CACHE (f) ? FRAME_IMAGE_CACHE (f)->refcount : 0;
+#ifdef GLYPH_DEBUG
   dpyinfo_refcount = dpyinfo->reference_count;
 #endif /* GLYPH_DEBUG */