impl(spanner): add support for Read Lock Mode in RW transactions

google/cloud/spanner/integration_tests/client_integration_test.cc

@@ -16,6 +16,7 @@
 #include "google/cloud/spanner/client.h"
 #include "google/cloud/spanner/database.h"
 #include "google/cloud/spanner/mutations.h"
+#include "google/cloud/spanner/options.h"
 #include "google/cloud/spanner/testing/database_integration_test.h"
 #include "google/cloud/credentials.h"
 #include "google/cloud/internal/getenv.h"
@@ -787,6 +788,34 @@ void CheckExecuteQueryWithSingleUseOptions(
   EXPECT_THAT(actual_rows, UnorderedElementsAreArray(expected_rows));
 }
 
+TEST_F(ClientIntegrationTest, ReadLockModeOptionIsSent) {
+  auto const singer_id = 101;
+  auto mutation_helper = [singer_id](std::string const& new_name) {
+    return Mutations{MakeInsertOrUpdateMutation(
+        "Singers", {"SingerId", "FirstName"}, singer_id, new_name)};
+  };
+
+  // Initial insert
+  auto insert = client_->Commit(mutation_helper("InitialName"));
+  ASSERT_STATUS_OK(insert);
+
+  auto read_lock_mode = Transaction::ReadLockMode::kOptimistic;
+  auto tx_a =
+      MakeReadWriteTransaction(Transaction::ReadWriteOptions(read_lock_mode));
+  auto tx_a_read_result = client_->Read(
+      tx_a, "Singers", KeySet().AddKey(MakeKey(singer_id)), {"SingerId"});
+  for (auto const& row : StreamOf<std::tuple<std::int64_t>>(tx_a_read_result)) {
+    EXPECT_STATUS_OK(row);
+  }
+  tx_a = MakeReadWriteTransaction(
+      tx_a, Transaction::ReadWriteOptions(read_lock_mode));
+
+  auto optimistic_result =
+      client_->Commit(tx_a, mutation_helper("SecondModifiedName"));
+
+  EXPECT_STATUS_OK(optimistic_result);
+}
+
 /// @test Test ExecuteQuery() with bounded staleness set by a timestamp.
 TEST_F(ClientIntegrationTest, ExecuteQueryBoundedStalenessTimestamp) {
   CheckExecuteQueryWithSingleUseOptions(

google/cloud/spanner/transaction.cc

@@ -34,6 +34,26 @@ google::protobuf::Duration ToProto(std::chrono::nanoseconds ns) {
   return proto;
 }
 
+google::spanner::v1::TransactionOptions_ReadWrite_ReadLockMode
+ProtoReadLockMode(
+    absl::optional<Transaction::ReadLockMode> const& read_lock_mode) {
+  if (!read_lock_mode) {
+    return google::spanner::v1::TransactionOptions_ReadWrite_ReadLockMode::
+        TransactionOptions_ReadWrite_ReadLockMode_READ_LOCK_MODE_UNSPECIFIED;
+  }
+  switch (*read_lock_mode) {
+    case Transaction::ReadLockMode::kOptimistic:
+      return google::spanner::v1::TransactionOptions_ReadWrite_ReadLockMode::
+          TransactionOptions_ReadWrite_ReadLockMode_OPTIMISTIC;
+    case Transaction::ReadLockMode::kPessimistic:
+      return google::spanner::v1::TransactionOptions_ReadWrite_ReadLockMode::
+          TransactionOptions_ReadWrite_ReadLockMode_PESSIMISTIC;
+    default:
+      return google::spanner::v1::TransactionOptions_ReadWrite_ReadLockMode::
+          TransactionOptions_ReadWrite_ReadLockMode_READ_LOCK_MODE_UNSPECIFIED;
+  }
+}
+
 google::spanner::v1::TransactionOptions MakeOpts(
     google::spanner::v1::TransactionOptions_ReadOnly ro_opts) {
   google::spanner::v1::TransactionOptions opts;
@@ -71,7 +91,11 @@ Transaction::ReadOnlyOptions::ReadOnlyOptions(
   ro_opts_.set_return_read_timestamp(true);
 }
 
-Transaction::ReadWriteOptions::ReadWriteOptions() = default;  // currently none
+Transaction::ReadWriteOptions::ReadWriteOptions() = default;
+
+Transaction::ReadWriteOptions::ReadWriteOptions(ReadLockMode read_lock_mode) {
+  rw_opts_.set_read_lock_mode(ProtoReadLockMode(read_lock_mode));
+}
 
 Transaction::ReadWriteOptions& Transaction::ReadWriteOptions::WithTag(
     absl::optional<std::string> tag) {

google/cloud/spanner/transaction.h

@@ -78,14 +78,28 @@ class Transaction {
     google::spanner::v1::TransactionOptions_ReadOnly ro_opts_;
   };
 
+  /**
+   * Read lock mode for ReadWrite transactions
+   * The Spanner V1 Transaction proto classes have their own enum
+   * implementations.
+   * See google::spanner::v1::TransactionOptions_ReadWrite_ReadLockMode
+   * This is a shorthand convenience for the developer.
+   */
+  enum class ReadLockMode {
+    kUnspecified,
+    kPessimistic,
+    kOptimistic,
+  };
+
   /**
    * Options for ReadWrite transactions.
    */
   class ReadWriteOptions {
    public:
-    // There are currently no read-write options.
     ReadWriteOptions();
 
+    explicit ReadWriteOptions(ReadLockMode read_lock_mode);
+
     // A tag used for collecting statistics about the transaction.
     ReadWriteOptions& WithTag(absl::optional<std::string> tag);
 

google/cloud/spanner/transaction_test.cc

@@ -33,6 +33,8 @@ TEST(TransactionOptions, Construction) {
   Transaction::ReadOnlyOptions exact_dur(staleness);
 
   Transaction::ReadWriteOptions none;
+  Transaction::ReadWriteOptions rw_with_read_lock(
+      Transaction::ReadLockMode::kOptimistic);
 
   Transaction::SingleUseOptions su_strong(strong);
   Transaction::SingleUseOptions su_exact_ts(exact_ts);
@@ -167,6 +169,47 @@ TEST(Transaction, MultiplexedPreviousTransactionId) {
       });
 }
 
+TEST(Transaction, ReadWriteOptionsWithTag) {
+  auto opts = Transaction::ReadWriteOptions().WithTag("test-tag");
+  Transaction txn = MakeReadWriteTransaction(opts);
+  spanner_internal::Visit(
+      txn, [&](spanner_internal::SessionHolder& /*session*/,
+               StatusOr<google::spanner::v1::TransactionSelector>& s,
+               spanner_internal::TransactionContext const& ctx) {
+        EXPECT_TRUE(s->has_begin());
+        EXPECT_TRUE(s->begin().has_read_write());
+        EXPECT_EQ(ctx.tag, "test-tag");
+        return 0;
+      });
+}
+
+TEST(Transaction, ReadWriteOptionsWithReadLockMode) {
+  auto check_lock_mode =
+      [](Transaction::ReadLockMode mode,
+         google::spanner::v1::TransactionOptions_ReadWrite_ReadLockMode
+             expected_proto_mode) {
+        auto opts = Transaction::ReadWriteOptions(mode);
+        Transaction txn = MakeReadWriteTransaction(opts);
+        spanner_internal::Visit(
+            txn, [&](spanner_internal::SessionHolder& /*session*/,
+                     StatusOr<google::spanner::v1::TransactionSelector>& s,
+                     spanner_internal::TransactionContext const& /*ctx*/) {
+              EXPECT_TRUE(s->has_begin());
+              EXPECT_TRUE(s->begin().has_read_write());
+              EXPECT_EQ(s->begin().read_write().read_lock_mode(),
+                        expected_proto_mode);
+              return 0;
+            });
+      };
+
+  check_lock_mode(
+      Transaction::ReadLockMode::kPessimistic,
+      google::spanner::v1::TransactionOptions_ReadWrite::PESSIMISTIC);
+  check_lock_mode(
+      Transaction::ReadLockMode::kOptimistic,
+      google::spanner::v1::TransactionOptions_ReadWrite::OPTIMISTIC);
+}
+
 }  // namespace
 GOOGLE_CLOUD_CPP_INLINE_NAMESPACE_END
 }  // namespace spanner