riot-audio-input-check: detect a synchronous access callback by thread

The handler read a flag the caller wrote without synchronization, and
inferred "called inside the request" from whether the call had returned,
which misfires when the handler runs on another thread first. Compare the
handler's thread with the caller's instead and keep the shared results
atomic.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

tools/riot-audio-input-check.cpp

@@ -9,6 +9,7 @@
 #include <atomic>
 #include <cstdio>
 #include <cstring>
+#include <pthread.h>
 #include <unistd.h>
 
 extern "C" void* const AVMediaTypeAudio;
@@ -49,15 +50,16 @@ static int authorization() {
     SEL status=sel_registerName("authorizationStatusForMediaType:");
     auto query=(long(*)(id,SEL,void*))objc_msgSend;
     long audio=query((id)device,status,AVMediaTypeAudio),video=query((id)device,status,AVMediaTypeVideo);
-    __block int granted=-1;
-    __block bool returned=false;
-    __block bool synchronous=false;
+    // macOS calls the handler on another queue, never on the requesting thread inside the call.
+    // Shared with the handler's thread, so atomic; read only after the handler signals.
+    static std::atomic<int> granted{-1};
+    static std::atomic<bool> synchronous{false};
+    const pthread_t caller=pthread_self();
     dispatch_semaphore_t done=dispatch_semaphore_create(0);
     auto request=(void(*)(id,SEL,void*,void(^)(BOOL)))objc_msgSend;
     request((id)device,sel_registerName("requestAccessForMediaType:completionHandler:"),AVMediaTypeAudio,^(BOOL value) {
-        synchronous=!returned;granted=value;dispatch_semaphore_signal(done);
+        synchronous=pthread_equal(pthread_self(),caller)!=0;granted=value;dispatch_semaphore_signal(done);
     });
-    returned=true;
     long waited=dispatch_semaphore_wait(done,dispatch_time(DISPATCH_TIME_NOW,2*NSEC_PER_SEC));
     printf("AUDIO_INPUT_AUTH audio=%ld video=%ld request_granted=%d async=%d\n",audio,video,(int)granted,!waited && !synchronous);
     fflush(stdout);