fix: object release in macOS (#453)

* Fix object release in macOS

Previously, we would release the image data provider, but not the
image.  We actually need to release the image, and not the data
provider.  This is based on the CoreFoundation "Create/Copy/Get"
ownership rules: we own things that we allocate with functions with
Create or Copy in their name, but not things that have Get in their
name.

I suspect that the CGImage held a reference to its data provider,
which stored the pixel data.  When we freed the data provider, we
released the pixel data, but not the CGImage structure.

Now, we're releasing the CGImage, and it releases the data provider.

Empirical testing while taking 10000 successive screenshots showed
that, once steady state was reached, the previous version was leaking
an average of about 467 bytes per screenshot on average.  The new
version still leaks about 148 bytes per screenshot, although that may
not be related to macOS.

Also fixed a few function types, but those were harmless.

* Remove unneeded function declaration, and add CHANGELOG entry

Author: jholveck

CHANGELOG.md

@@ -8,6 +8,7 @@ See Git checking messages for full history.
 - Linux: introduce an XCB-powered backend stack with a factory in ``mss.linux`` while keeping the Xlib code as a fallback (#425)
 - Linux: add the XShmGetImage backend with automatic XGetImage fallback and explicit status reporting (#431)
 - Windows: improve error checking and messages for Win32 API calls (#448)
+- Mac: fix memory leak (#450, #453)
 - :heart: contributors: @jholveck
 
 ## 10.1.0 (2025-08-16)

src/mss/darwin.py

@@ -9,7 +9,18 @@
 import ctypes
 import ctypes.util
 import sys
-from ctypes import POINTER, Structure, c_double, c_float, c_int32, c_ubyte, c_uint32, c_uint64, c_void_p
+from ctypes import (
+    POINTER,
+    Structure,
+    c_double,
+    c_float,
+    c_int32,
+    c_long,
+    c_size_t,
+    c_ubyte,
+    c_uint32,
+    c_void_p,
+)
 from platform import mac_ver
 from typing import TYPE_CHECKING, Any
 
@@ -75,17 +86,16 @@ def __repr__(self) -> str:
     # Syntax: cfunction: (attr, argtypes, restype)
     "CGDataProviderCopyData": ("core", [c_void_p], c_void_p),
     "CGDisplayBounds": ("core", [c_uint32], CGRect),
-    "CGDisplayRotation": ("core", [c_uint32], c_float),
-    "CFDataGetBytePtr": ("core", [c_void_p], c_void_p),
-    "CFDataGetLength": ("core", [c_void_p], c_uint64),
-    "CFRelease": ("core", [c_void_p], c_void_p),
-    "CGDataProviderRelease": ("core", [c_void_p], c_void_p),
+    "CGDisplayRotation": ("core", [c_uint32], c_double),
+    "CFDataGetBytePtr": ("core", [c_void_p], POINTER(c_ubyte)),
+    "CFDataGetLength": ("core", [c_void_p], c_long),
+    "CFRelease": ("core", [c_void_p], None),
     "CGGetActiveDisplayList": ("core", [c_uint32, POINTER(c_uint32), POINTER(c_uint32)], c_int32),
-    "CGImageGetBitsPerPixel": ("core", [c_void_p], int),
-    "CGImageGetBytesPerRow": ("core", [c_void_p], int),
+    "CGImageGetBitsPerPixel": ("core", [c_void_p], c_size_t),
+    "CGImageGetBytesPerRow": ("core", [c_void_p], c_size_t),
     "CGImageGetDataProvider": ("core", [c_void_p], c_void_p),
-    "CGImageGetHeight": ("core", [c_void_p], int),
-    "CGImageGetWidth": ("core", [c_void_p], int),
+    "CGImageGetHeight": ("core", [c_void_p], c_size_t),
+    "CGImageGetWidth": ("core", [c_void_p], c_size_t),
     "CGRectStandardize": ("core", [CGRect], CGRect),
     "CGRectUnion": ("core", [CGRect, CGRect], CGRect),
     "CGWindowListCreateImage": ("core", [CGRect, c_uint32, c_uint32, c_uint32], c_void_p),
@@ -197,7 +207,7 @@ def _grab_impl(self, monitor: Monitor, /) -> ScreenShot:
 
         width = core.CGImageGetWidth(image_ref)
         height = core.CGImageGetHeight(image_ref)
-        prov = copy_data = None
+        copy_data = None
         try:
             prov = core.CGImageGetDataProvider(image_ref)
             copy_data = core.CGDataProviderCopyData(prov)
@@ -219,10 +229,9 @@ def _grab_impl(self, monitor: Monitor, /) -> ScreenShot:
                     cropped.extend(data[start:end])
                 data = cropped
         finally:
-            if prov:
-                core.CGDataProviderRelease(prov)
             if copy_data:
                 core.CFRelease(copy_data)
+            core.CFRelease(image_ref)
 
         return self.cls_image(data, monitor, size=Size(width, height))