Fix race condition caused by mstats replacing it call with malloc_zone_statistics(). #15501

FirebasePerformance/Sources/Gauges/Memory/FPRMemoryGaugeCollector.m

@@ -37,10 +37,18 @@ @interface FPRMemoryGaugeCollector ()
 FPRMemoryGaugeData *fprCollectMemoryMetric(void) {
   NSDate *collectionTime = [NSDate date];
 
-  struct mstats ms = mstats();
-  FPRMemoryGaugeData *gaugeData = [[FPRMemoryGaugeData alloc] initWithCollectionTime:collectionTime
-                                                                            heapUsed:ms.bytes_used
-                                                                       heapAvailable:ms.bytes_free];
+  // Use malloc_zone_statistics to get heap memory usage.
+  // Passing nil aggregates statistics from all malloc zones.
+  malloc_statistics_t stats;
+  malloc_zone_statistics(nil, &stats);
+  uint64_t usedBytes = stats.size_in_use;
+  uint64_t totalHeapBytes = stats.size_allocated;
+  uint64_t freeInsideHeap = totalHeapBytes - usedBytes;
+
+  FPRMemoryGaugeData *gaugeData =
+      [[FPRMemoryGaugeData alloc] initWithCollectionTime:collectionTime
+                                                heapUsed:usedBytes
+                                           heapAvailable:freeInsideHeap];
   return gaugeData;
 }
 

FirebasePerformance/Sources/Gauges/Memory/FPRMemoryGaugeData.h

@@ -24,10 +24,13 @@ NS_ASSUME_NONNULL_BEGIN
 /** @brief Time at which memory data was measured. */
 @property(nonatomic, readonly) NSDate *collectionTime;
 
-/** @brief Heap memory that is used. */
+/** @brief Physical memory footprint of the application, measured via task_info phys_footprint.
+ *  Note: This represents the total memory used by the process (as reported by Jetsam accounting),
+ *  not just heap allocations. It includes heap, stack, memory-mapped files, and other resources. */
 @property(nonatomic, readonly) u_long heapUsed;
 
-/** @brief Heap memory that is available. */
+/** @brief Heap memory that is available within allocated heap space (size_allocated - size_in_use).
+ */
 @property(nonatomic, readonly) u_long heapAvailable;
 
 - (instancetype)init NS_UNAVAILABLE;
@@ -36,8 +39,9 @@ NS_ASSUME_NONNULL_BEGIN
  * Creates an instance of memory gauge data with the provided information.
  *
  * @param collectionTime Time at which the gauge data was collected.
- * @param heapUsed Heap memory that is used.
- * @param heapAvailable Heap memory that is available.
+ * @param heapUsed Physical memory footprint of the application (measured via task_info
+ * phys_footprint).
+ * @param heapAvailable Free memory within allocated heap space (size_allocated - size_in_use).
  * @return Instance of memory gauge data.
  */
 - (instancetype)initWithCollectionTime:(NSDate *)collectionTime