Backport PR matplotlib#28981: FIX: macos: Use standard NSApp run loop in our input hook

Author: tacaswell

src/_macosx.m

@@ -40,60 +40,84 @@
 static bool keyChangeCapsLock = false;
 /* Keep track of the current mouse up/down state for open/closed cursor hand */
 static bool leftMouseGrabbing = false;
-/* Keep track of whether stdin has been received */
-static bool stdin_received = false;
-static bool stdin_sigint = false;
 // Global variable to store the original SIGINT handler
 static PyOS_sighandler_t originalSigintAction = NULL;
 
-// Signal handler for SIGINT, only sets a flag to exit the run loop
+// Stop the current app's run loop, sending an event to ensure it actually stops
+static void stopWithEvent() {
+    [NSApp stop: nil];
+    // Post an event to trigger the actual stopping.
+    [NSApp postEvent: [NSEvent otherEventWithType: NSEventTypeApplicationDefined
+                                         location: NSZeroPoint
+                                    modifierFlags: 0
+                                        timestamp: 0
+                                     windowNumber: 0
+                                          context: nil
+                                          subtype: 0
+                                            data1: 0
+                                            data2: 0]
+             atStart: YES];
+}
+
+// Signal handler for SIGINT, only argument matching for stopWithEvent
 static void handleSigint(int signal) {
-    stdin_sigint = true;
+    stopWithEvent();
+}
+
+// Helper function to flush all events.
+// This is needed in some instances to ensure e.g. that windows are properly closed.
+// It is used in the input hook as well as wrapped in a version callable from Python.
+static void flushEvents() {
+    while (true) {
+        NSEvent* event = [NSApp nextEventMatchingMask: NSEventMaskAny
+                                            untilDate: [NSDate distantPast]
+                                               inMode: NSDefaultRunLoopMode
+                                              dequeue: YES];
+        if (!event) {
+            break;
+        }
+        [NSApp sendEvent:event];
+    }
 }
 
 static int wait_for_stdin() {
-    @autoreleasepool {
-        stdin_received = false;
-        stdin_sigint = false;
+    // Short circuit if no windows are active
+    // Rely on Python's input handling to manage CPU usage
+    // This queries the NSApp, rather than using our FigureWindowCount because that is decremented when events still
+    // need to be processed to properly close the windows.
+    if (![[NSApp windows] count]) {
+      flushEvents();
+      return 1;
+    }
 
+    @autoreleasepool {
         // Set up a SIGINT handler to interrupt the event loop if ctrl+c comes in too
         originalSigintAction = PyOS_setsig(SIGINT, handleSigint);
 
         // Create an NSFileHandle for standard input
         NSFileHandle *stdinHandle = [NSFileHandle fileHandleWithStandardInput];
 
+
         // Register for data available notifications on standard input
-        [[NSNotificationCenter defaultCenter] addObserverForName: NSFileHandleDataAvailableNotification
-                                                          object: stdinHandle
-                                                           queue: [NSOperationQueue mainQueue] // Use the main queue
-                                                      usingBlock: ^(NSNotification *notification) {
-                                                                    // Mark that input has been received
-                                                                    stdin_received = true;
-                                                                    }
+        id notificationID = [[NSNotificationCenter defaultCenter] addObserverForName: NSFileHandleDataAvailableNotification
+                                                                              object: stdinHandle
+                                                                               queue: [NSOperationQueue mainQueue] // Use the main queue
+                                                                          usingBlock: ^(NSNotification *notification) {stopWithEvent();}
         ];
 
         // Wait in the background for anything that happens to stdin
         [stdinHandle waitForDataInBackgroundAndNotify];
 
-        // continuously run an event loop until the stdin_received flag is set to exit
-        while (!stdin_received && !stdin_sigint) {
-            // This loop is similar to the main event loop and flush_events which have
-            // Py_[BEGIN|END]_ALLOW_THREADS surrounding the loop.
-            // This should not be necessary here because PyOS_InputHook releases the GIL for us.
-            while (true) {
-                NSEvent *event = [NSApp nextEventMatchingMask: NSEventMaskAny
-                                                    untilDate: [NSDate distantPast]
-                                                       inMode: NSDefaultRunLoopMode
-                                                      dequeue: YES];
-                if (!event) { break; }
-                [NSApp sendEvent: event];
-            }
-        }
+        // Run the application's event loop, which will be interrupted on stdin or SIGINT
+        [NSApp run];
+
         // Remove the input handler as an observer
-        [[NSNotificationCenter defaultCenter] removeObserver: stdinHandle];
+        [[NSNotificationCenter defaultCenter] removeObserver: notificationID];
+
 
         // Restore the original SIGINT handler upon exiting the function
         PyOS_setsig(SIGINT, originalSigintAction);
+
         return 1;
     }
 }
@@ -236,18 +260,7 @@ static void lazy_init(void) {
 static PyObject*
 stop(PyObject* self)
 {
-    [NSApp stop: nil];
-    // Post an event to trigger the actual stopping.
-    [NSApp postEvent: [NSEvent otherEventWithType: NSEventTypeApplicationDefined
-                                         location: NSZeroPoint
-                                    modifierFlags: 0
-                                        timestamp: 0
-                                     windowNumber: 0
-                                          context: nil
-                                          subtype: 0
-                                            data1: 0
-                                            data2: 0]
-             atStart: YES];
+    stopWithEvent();
     Py_RETURN_NONE;
 }
 
@@ -382,20 +395,9 @@ static CGFloat _get_device_scale(CGContextRef cr)
     // We run the app, matching any events that are waiting in the queue
     // to process, breaking out of the loop when no events remain and
     // displaying the canvas if needed.
-    NSEvent *event;
-
     Py_BEGIN_ALLOW_THREADS
 
-    while (true) {
-        event = [NSApp nextEventMatchingMask: NSEventMaskAny
-                                   untilDate: [NSDate distantPast]
-                                      inMode: NSDefaultRunLoopMode
-                                     dequeue: YES];
-        if (!event) {
-            break;
-        }
-        [NSApp sendEvent:event];
-    }
+    flushEvents();
 
     Py_END_ALLOW_THREADS