Ignore multiple transaction commit/rollback/close.

db.go

@@ -571,7 +571,7 @@ func (db *DB) Stat() (*Stat, error) {
 
 // page retrieves a page reference from the mmap based on the current page size.
 func (db *DB) page(id pgid) *page {
-	pos := id*pgid(db.pageSize)
+	pos := id * pgid(db.pageSize)
 	return (*page)(unsafe.Pointer(&db.data[pos]))
 }
 

rwtransaction.go

@@ -82,6 +82,10 @@ func (t *RWTransaction) DeleteBucket(name string) error {
 // Commit writes all changes to disk and updates the meta page.
 // Returns an error if a disk write error occurs.
 func (t *RWTransaction) Commit() error {
+	if t.db == nil {
+		return nil
+	}
+
 	defer t.close()
 
 	// TODO(benbjohnson): Use vectorized I/O to write out dirty pages.
@@ -119,7 +123,10 @@ func (t *RWTransaction) Rollback() {
 }
 
 func (t *RWTransaction) close() {
-	t.db.rwlock.Unlock()
+	if t.db != nil {
+		t.db.rwlock.Unlock()
+		t.db = nil
+	}
 }
 
 // allocate returns a contiguous block of memory starting at a given page.

transaction.go

@@ -40,10 +40,14 @@ func (t *Transaction) id() txnid {
 
 // Close closes the transaction and releases any pages it is using.
 func (t *Transaction) Close() {
-	if t.rwtransaction != nil {
-		t.rwtransaction.Rollback()
+	if t.db != nil {
+		if t.rwtransaction != nil {
+			t.rwtransaction.Rollback()
+		} else {
+			t.db.removeTransaction(t)
+			t.db = nil
+		}
 	}
-	t.db.removeTransaction(t)
 }
 
 // DB returns a reference to the database that created the transaction.