prevent segfault after mmap failure

Author: lukechampine

db.go

@@ -39,6 +39,8 @@ const (
 // default page size for db is set to the OS page size.
 var defaultPageSize = os.Getpagesize()
 
+var ErrDiskFull = errors.New("db cannot grow, likely due to lack of disk space")
+
 // DB represents a collection of buckets persisted to a file on disk.
 // All data access is performed through transactions which can be obtained through the DB.
 // All the functions on DB will return a ErrDatabaseNotOpen if accessed before Open() is called.
@@ -109,6 +111,7 @@ type DB struct {
 	txs      []*Tx
 	freelist *freelist
 	stats    Stats
+	unusable bool // true if mmap has failed
 
 	pagePool sync.Pool
 
@@ -480,6 +483,10 @@ func (db *DB) beginTx() (*Tx, error) {
 		db.metalock.Unlock()
 		return nil, ErrDatabaseNotOpen
 	}
+	// Exit if database is unusable.
+	if db.unusable {
+		return nil, ErrDiskFull
+	}
 
 	// Create a transaction associated with the database.
 	t := &Tx{}
@@ -521,6 +528,10 @@ func (db *DB) beginRWTx() (*Tx, error) {
 		db.rwlock.Unlock()
 		return nil, ErrDatabaseNotOpen
 	}
+	// Exit if database is unusable.
+	if db.unusable {
+		return nil, ErrDiskFull
+	}
 
 	// Create a transaction associated with the database.
 	t := &Tx{writable: true}

tx.go

@@ -161,7 +161,13 @@ func (tx *Tx) Commit() error {
 	// spill data onto dirty pages.
 	startTime = time.Now()
 	if err := tx.root.spill(); err != nil {
-		tx.rollback()
+		// If spill fails, it's because dirty pages cannot be allocated. This
+		// leaves the db in an unusable state, so set a flag to prevent future
+		// access. Also, we must call tx.close directly instead of tx.rollback
+		// to prevent a segfault on Windows.
+		// https://github.com/boltdb/bolt/issues/706
+		tx.db.unusable = true
+		tx.close()
 		return err
 	}
 	tx.stats.SpillTime += time.Since(startTime)