Add support for CDB backed by mmap-ed memory.

mmap.go

@@ -0,0 +1,66 @@
+
+
+package cdb
+
+
+import "errors"
+import "os"
+import "syscall"
+
+
+
+
+// Open opens an existing CDB database at the given path, using `mmap`-ed memory.
+func OpenMmap (_path string) (*CDB, error) {
+	if _file, _error := os.Open (_path); _error == nil {
+		return NewFromMappedWithHasher (_file, nil)
+	} else {
+		return nil, _error
+	}
+}
+
+
+func NewFromMappedWithHasher (_file *os.File, _hasher func ([]byte) (uint32)) (*CDB, error) {
+	var _size int64
+	if _stat, _error := _file.Stat (); _error == nil {
+		_size = _stat.Size ()
+	} else {
+		return nil, _error
+	}
+	if _size < 1024 {
+		return nil, errors.New ("file is too small (or empty)")
+	}
+	if _size >= (4 * 1024 * 1024 * 1024) {
+		return nil, errors.New ("file is too large")
+	}
+	var _data []byte
+	if _data_0, _error := syscall.Mmap (int (_file.Fd ()), 0, int (_size), syscall.PROT_READ, syscall.MAP_SHARED); _error == nil {
+		_data = _data_0
+	} else {
+		return nil, _error
+	}
+	_cdb, _error := NewFromBufferWithHasher (_data, _hasher)
+	if _error != nil {
+		_cdb.readerCloser = & mmapCloser { data : _data }
+	}
+	return _cdb, _error
+}
+
+
+
+
+type mmapCloser struct {
+	data []byte
+}
+
+
+func (_closer *mmapCloser) Close () (error) {
+	if _closer.data != nil {
+		_error := syscall.Munmap (_closer.data)
+		_closer.data = nil
+		return _error
+	} else {
+		return nil
+	}
+}
+

mmap_test.go

@@ -0,0 +1,43 @@
+
+package cdb_test
+
+import (
+	"math/rand"
+	"testing"
+	"time"
+
+	"github.com/colinmarc/cdb"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+
+func TestGetMmap(t *testing.T) {
+	db, err := cdb.OpenMmap("./test/test.cdb")
+	require.NoError(t, err)
+	require.NotNil(t, db)
+
+	records := append(append(expectedRecords, expectedRecords...), expectedRecords...)
+	shuffle(records)
+
+	for _, record := range records {
+		msg := "while fetching " + string(record[0])
+
+		value, err := db.Get(record[0])
+		require.NoError(t, err, msg)
+		assert.Equal(t, string(record[1]), string(value), msg)
+	}
+}
+
+
+func BenchmarkGetMmap(b *testing.B) {
+	db, _ := cdb.OpenMmap("./test/test.cdb")
+	b.ResetTimer()
+
+	rand.Seed(time.Now().UnixNano())
+	for i := 0; i < b.N; i++ {
+		record := expectedRecords[rand.Intn(len(expectedRecords))]
+		db.Get(record[0])
+	}
+}
+