backend: Hooks interface & implementation.

server/mvcc/backend/backend.go

@@ -104,6 +104,8 @@ type backend struct {
 	stopc chan struct{}
 	donec chan struct{}
 
+	hooks Hooks
+
 	lg *zap.Logger
 }
 
@@ -124,6 +126,9 @@ type BackendConfig struct {
 	UnsafeNoFsync bool `json:"unsafe-no-fsync"`
 	// Mlock prevents backend database file to be swapped
 	Mlock bool
+
+	// Hooks are getting executed during lifecycle of Backend's transactions.
+	Hooks Hooks
 }
 
 func DefaultBackendConfig() BackendConfig {
@@ -189,6 +194,9 @@ func newBackend(bcfg BackendConfig) *backend {
 		lg: bcfg.Logger,
 	}
 	b.batchTx = newBatchTxBuffered(b)
+	// We set it after newBatchTxBuffered to skip the 'empty' commit.
+	b.hooks = bcfg.Hooks
+
 	go b.run()
 	return b
 }

server/mvcc/backend/batch_tx.go

@@ -109,6 +109,7 @@ func (t *batchTx) unsafePut(bucketName []byte, key []byte, value []byte, seq boo
 		t.backend.lg.Fatal(
 			"failed to find a bucket",
 			zap.String("bucket-name", string(bucketName)),
+			zap.Stack("stack"),
 		)
 	}
 	if seq {
@@ -133,6 +134,7 @@ func (t *batchTx) UnsafeRange(bucketName, key, endKey []byte, limit int64) ([][]
 		t.backend.lg.Fatal(
 			"failed to find a bucket",
 			zap.String("bucket-name", string(bucketName)),
+			zap.Stack("stack"),
 		)
 	}
 	return unsafeRange(bucket.Cursor(), key, endKey, limit)
@@ -167,6 +169,7 @@ func (t *batchTx) UnsafeDelete(bucketName []byte, key []byte) {
 		t.backend.lg.Fatal(
 			"failed to find a bucket",
 			zap.String("bucket-name", string(bucketName)),
+			zap.Stack("stack"),
 		)
 	}
 	err := bucket.Delete(key)
@@ -283,6 +286,10 @@ func (t *batchTxBuffered) CommitAndStop() {
 }
 
 func (t *batchTxBuffered) commit(stop bool) {
+	if t.backend.hooks != nil {
+		t.backend.hooks.OnPreCommitUnsafe(t)
+	}
+
 	// all read txs must be closed to acquire boltdb commit rwlock
 	t.backend.readTx.Lock()
 	t.unsafeCommit(stop)

server/mvcc/backend/hooks.go

@@ -0,0 +1,36 @@
+// Copyright 2021 The etcd Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package backend
+
+type HookFunc func(tx BatchTx)
+
+// Hooks allow to add additional logic executed during transaction lifetime.
+type Hooks interface {
+	// OnPreCommitUnsafe is executed before Commit of transactions.
+	// The given transaction is already locked.
+	OnPreCommitUnsafe(tx BatchTx)
+}
+
+type hooks struct {
+	onPreCommitUnsafe HookFunc
+}
+
+func (h hooks) OnPreCommitUnsafe(tx BatchTx) {
+	h.onPreCommitUnsafe(tx)
+}
+
+func NewHooks(onPreCommitUnsafe HookFunc) Hooks {
+	return hooks{onPreCommitUnsafe: onPreCommitUnsafe}
+}