Use a single, shared executor for running transactions

PiperOrigin-RevId: 312338832

Author: wilhuff

firestore/src/ios/firestore_ios.cc

@@ -53,7 +53,9 @@ FirestoreInternal::FirestoreInternal(App* app)
 FirestoreInternal::FirestoreInternal(
     App* app, std::unique_ptr<CredentialsProvider> credentials)
     : app_(NOT_NULL(app)),
-      firestore_core_(CreateFirestore(app, std::move(credentials))) {
+      firestore_core_(CreateFirestore(app, std::move(credentials))),
+      transaction_executor_(absl::ShareUniquePtr(Executor::CreateConcurrent(
+          "com.google.firebase.firestore.transaction", /*threads=*/5))) {
   ApplyDefaultSettings();
 }
 
@@ -130,8 +132,7 @@ Future<void> FirestoreInternal::RunTransaction(TransactionFunction* update) {
 
 Future<void> FirestoreInternal::RunTransaction(
     std::function<Error(Transaction&, std::string&)> update) {
-  auto executor = absl::ShareUniquePtr(Executor::CreateConcurrent(
-      "com.google.firebase.firestore.transaction", /*threads=*/5));
+  auto executor = transaction_executor_;
   auto promise =
       promise_factory_.CreatePromise<void>(AsyncApi::kRunTransaction);
 

firestore/src/ios/firestore_ios.h

@@ -27,6 +27,10 @@ class Transaction;
 class TransactionFunction;
 class WriteBatch;
 
+namespace util {
+class Executor;
+}
+
 class FirestoreInternal {
  public:
   // Note: call `set_firestore_public` immediately after construction.
@@ -145,6 +149,8 @@ class FirestoreInternal {
   // TODO(b/136119216): revamp this mechanism on both iOS and Android.
   std::mutex listeners_mutex_;
   std::unordered_set<ListenerRegistrationInternal*> listeners_;
+
+  std::shared_ptr<util::Executor> transaction_executor_;
 };
 
 }  // namespace firestore