Make FutureManager not delete futures if they are still referenced externally.

A recent change to reference counted future impl made IsSafeToDelete only check if the underlying logic determined if it was safe, which was needed when deleting Auth futures directly. This made FutureManager a bit hasty in deleting things, which instead should be checking if those Futures are still being referenced by someone else.

PiperOrigin-RevId: 264503406

Author: a-maurice

app/src/future_manager.cc

@@ -120,7 +120,8 @@ void FutureManager::CleanupOrphanedFutureApis(bool force_delete_all) {
 
 bool FutureManager::IsSafeToDeleteFutureApi(ReferenceCountedFutureImpl* api) {
   MutexLock lock(future_api_mutex_);
-  return api ? api->IsSafeToDelete() : false;
+  return api ? api->IsSafeToDelete() && !api->IsReferencedExternally()
+             : false;
 }
 
 // NOLINTNEXTLINE - allow namespace overridden

app/src/reference_counted_future_impl.cc

@@ -21,6 +21,7 @@
 
 #include "app/src/assert.h"
 #include "app/src/log.h"
+#include "app/src/mutex.h"
 
 // Set this to 1 to enable verbose logging in this module.
 #if !defined(FIREBASE_FUTURE_TRACE_ENABLE)
@@ -510,6 +511,27 @@ bool ReferenceCountedFutureImpl::IsSafeToDelete() const {
   return true;
 }
 
+bool ReferenceCountedFutureImpl::IsReferencedExternally() const {
+  MutexLock lock(mutex_);
+
+  int total_references = 0;
+  int internal_references = 0;
+  for (auto i = backings_.begin(); i != backings_.end(); ++i) {
+    // Count the total number of references to all valid Futures.
+    total_references += i->second->reference_count;
+  }
+  for (int i = 0; i < last_results_.size(); i++) {
+    if (last_results_[i].status() != kFutureStatusInvalid) {
+      // If the status is not invalid, this entry is using up a reference.
+      // Count up the internal references.
+      internal_references++;
+    }
+  }
+  // If there are more references than the internal ones, someone is holding
+  // onto a Future.
+  return total_references > internal_references;
+}
+
 void ReferenceCountedFutureImpl::SetContextData(
     FutureHandle handle, void* context_data,
     void (*delete_context_data_fn)(void* data_to_delete)) {

app/src/reference_counted_future_impl.h

@@ -369,6 +369,10 @@ class ReferenceCountedFutureImpl : public detail::FutureApiInterface {
   /// no futures are Pending.
   bool IsSafeToDelete() const;
 
+  /// Check if the Future is being referenced by something other than
+  /// last_results_.
+  bool IsReferencedExternally() const;
+
   /// Sets temporary context data associated with a FutureHandle that will be
   /// deallocated alongside the FutureBackingData. This will occur when there
   /// are no more Futures referencing it.