fix(macos): prevent indefinite hanging if screen capture is not granted (#3360)

src/platform/macos/display.mm

@@ -5,6 +5,7 @@
 #include "src/platform/common.h"
 #include "src/platform/macos/av_img_t.h"
 #include "src/platform/macos/av_video.h"
+#include "src/platform/macos/misc.h"
 #include "src/platform/macos/nv12_zero_device.h"
 
 #include "src/config.h"
@@ -100,6 +101,13 @@ namespace platf {
 
     int
     dummy_img(img_t *img) override {
+      if (!platf::is_screen_capture_allowed()) {
+        // If we don't have the screen capture permission, this function will hang
+        // indefinitely without doing anything useful. Exit instead to avoid this.
+        // A non-zero return value indicates failure to the calling function.
+        return 1;
+      }
+
       auto signal = [av_capture capture:^(CMSampleBufferRef sampleBuffer) {
         auto new_sample_buffer = std::make_shared<av_sample_buf_t>(sampleBuffer);
         auto new_pixel_buffer = std::make_shared<av_pixel_buf_t>(new_sample_buffer->buf);

src/platform/macos/misc.h

@@ -8,6 +8,11 @@
 
 #include <CoreGraphics/CoreGraphics.h>
 
+namespace platf {
+  bool
+  is_screen_capture_allowed();
+}
+
 namespace dyn {
   typedef void (*apiproc)();
 

src/platform/macos/misc.mm

@@ -42,6 +42,16 @@ namespace platf {
   CGRequestScreenCaptureAccess(void) __attribute__((weak_import));
 #endif
 
+  namespace {
+    auto screen_capture_allowed = std::atomic<bool> { false };
+  }  // namespace
+
+  // Return whether screen capture is allowed for this process.
+  bool
+  is_screen_capture_allowed() {
+    return screen_capture_allowed;
+  }
+
   std::unique_ptr<deinit_t>
   init() {
     // This will generate a warning about CGPreflightScreenCaptureAccess and
@@ -68,6 +78,8 @@ namespace platf {
       return nullptr;
     }
 #pragma clang diagnostic pop
+    // Record that we determined that we have the screen capture permission.
+    screen_capture_allowed = true;
     return std::make_unique<deinit_t>();
   }