Update to last common bleve (#3986)

vendor/github.com/couchbase/vellum/vellum_mmap.go

@@ -0,0 +1,60 @@
+//  Copyright (c) 2017 Couchbase, Inc.
+//
+// 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.
+
+// +build !nommap
+
+package vellum
+
+import (
+	"os"
+
+	mmap "github.com/edsrzf/mmap-go"
+)
+
+type mmapWrapper struct {
+	f  *os.File
+	mm mmap.MMap
+}
+
+func (m *mmapWrapper) Close() (err error) {
+	if m.mm != nil {
+		err = m.mm.Unmap()
+	}
+	// try to close file even if unmap failed
+	if m.f != nil {
+		err2 := m.f.Close()
+		if err == nil {
+			// try to return first error
+			err = err2
+		}
+	}
+	return
+}
+
+func open(path string) (*FST, error) {
+	f, err := os.Open(path)
+	if err != nil {
+		return nil, err
+	}
+	mm, err := mmap.Map(f, mmap.RDONLY, 0)
+	if err != nil {
+		// mmap failed, try to close the file
+		_ = f.Close()
+		return nil, err
+	}
+	return new(mm, &mmapWrapper{
+		f:  f,
+		mm: mm,
+	})
+}