storage: add a simple backend and kv example

storage/backend/batch_tx.go

@@ -0,0 +1,98 @@
+package backend
+
+import (
+	"bytes"
+	"log"
+	"sync"
+
+	"github.com/boltdb/bolt"
+)
+
+type BatchTx interface {
+	Lock()
+	Unlock()
+	UnsafeCreateBucket(name []byte)
+	UnsafePut(bucketName []byte, key []byte, value []byte)
+	UnsafeRange(bucketName []byte, key, endKey []byte, limit int64) [][]byte
+	UnsafeDelete(bucketName []byte, key []byte)
+}
+
+type batchTx struct {
+	mu      sync.Mutex
+	tx      *bolt.Tx
+	backend *backend
+	pending int
+}
+
+func (t *batchTx) Lock() {
+	t.mu.Lock()
+}
+
+func (t *batchTx) Unlock() {
+	t.mu.Unlock()
+}
+
+func (t *batchTx) UnsafeCreateBucket(name []byte) {
+	_, err := t.tx.CreateBucket(name)
+	if err != nil && err != bolt.ErrBucketExists {
+		log.Fatalf("storage: cannot create bucket %s (%v)", string(name), err)
+	}
+}
+
+// before calling unsafePut, the caller MUST hold the lock on tnx.
+func (t *batchTx) UnsafePut(bucketName []byte, key []byte, value []byte) {
+	bucket := t.tx.Bucket(bucketName)
+	if bucket == nil {
+		log.Fatalf("storage: bucket %s does not exist", string(bucketName))
+	}
+	if err := bucket.Put(key, value); err != nil {
+		log.Fatalf("storage: cannot put key into bucket (%v)", err)
+	}
+	t.pending++
+	if t.pending > t.backend.batchLimit {
+		t.backend.commitAndBegin()
+		t.pending = 0
+	}
+}
+
+// before calling unsafeRange, the caller MUST hold the lock on tnx.
+func (t *batchTx) UnsafeRange(bucketName []byte, key, endKey []byte, limit int64) [][]byte {
+	bucket := t.tx.Bucket(bucketName)
+	if bucket == nil {
+		log.Fatalf("storage: bucket %s does not exist", string(bucketName))
+	}
+
+	var vs [][]byte
+
+	if len(endKey) == 0 {
+		if v := bucket.Get(key); v == nil {
+			return vs
+		} else {
+			return append(vs, v)
+		}
+	}
+
+	c := bucket.Cursor()
+	for ck, cv := c.Seek(key); ck != nil && bytes.Compare(ck, endKey) < 0; ck, cv = c.Next() {
+		vs = append(vs, cv)
+	}
+
+	return vs
+}
+
+// before calling unsafeDelete, the caller MUST hold the lock on tnx.
+func (t *batchTx) UnsafeDelete(bucketName []byte, key []byte) {
+	bucket := t.tx.Bucket(bucketName)
+	if bucket == nil {
+		log.Fatalf("storage: bucket %s does not exist", string(bucketName))
+	}
+	err := bucket.Delete(key)
+	if err != nil {
+		log.Fatalf("storage: cannot delete key from bucket (%v)", err)
+	}
+	t.pending++
+	if t.pending > t.backend.batchLimit {
+		t.backend.commitAndBegin()
+		t.pending = 0
+	}
+}