Fix a race condition involving binary images being changed. (#7459)

Author: elenadoty

Crashlytics/CHANGELOG.md

@@ -1,3 +1,6 @@
+# Unreleased
+- [changed] Updated the performance improvements in 7.5.0 to avoid a possible race condition (#7459).
+
 # v7.5.0
 - [changed] Improve start-up performance by moving some initialization work to a background thread (#7332).
 - [changed] Updated upload-symbols to a version that is notarized to avoid macOS security alerts (#7323).

Crashlytics/Crashlytics/Components/FIRCLSBinaryImage.m

@@ -363,17 +363,16 @@ static void FIRCLSBinaryImageChanged(bool added,
                                      const struct mach_header* mh,
                                      intptr_t vmaddr_slide) {
   //    FIRCLSSDKLog("Binary image %s %p\n", added ? "loaded" : "unloaded", mh);
+  FIRCLSBinaryImageDetails imageDetails;
+  memset(&imageDetails, 0, sizeof(FIRCLSBinaryImageDetails));
+
+  imageDetails.slice = FIRCLSMachOSliceWithHeader((void*)mh);
+  imageDetails.vmaddr_slide = vmaddr_slide;
+  FIRCLSBinaryImageFillInImageDetails(&imageDetails);
 
   // Do these time-consuming operations on a background queue
   dispatch_async(FIRCLSGetBinaryImageQueue(), ^{
-    FIRCLSBinaryImageDetails imageDetails;
-
-    memset(&imageDetails, 0, sizeof(FIRCLSBinaryImageDetails));
-
-    imageDetails.slice = FIRCLSMachOSliceWithHeader((void*)mh);
-    imageDetails.vmaddr_slide = vmaddr_slide;
-    FIRCLSBinaryImageFillInImageDetails(&imageDetails);
-
+    // this is an atomic operation
     FIRCLSBinaryImageStoreNode(added, imageDetails);
     FIRCLSBinaryImageRecordSlice(added, imageDetails);
   });