1 files changed, 21 insertions, 3 deletions
diff --git a/bolt_unix.go b/bolt_unix.go
index 35dce08..17ca318 100644
--- a/bolt_unix.go
+++ b/bolt_unix.go
@@ -11,7 +11,7 @@ import (
 )
 
 // flock acquires an advisory lock on a file descriptor.
-func flock(f *os.File, timeout time.Duration) error {
+func flock(f *os.File, exclusive bool, timeout time.Duration) error {
 	var t time.Time
 	for {
 		// If we're beyond our timeout then return an error.
@@ -21,9 +21,13 @@ func flock(f *os.File, timeout time.Duration) error {
 		} else if timeout > 0 && time.Since(t) > timeout {
 			return ErrTimeout
 		}
+		flag := syscall.LOCK_SH
+		if exclusive {
+			flag = syscall.LOCK_EX
+		}
 
 		// Otherwise attempt to obtain an exclusive lock.
-		err := syscall.Flock(int(f.Fd()), syscall.LOCK_EX|syscall.LOCK_NB)
+		err := syscall.Flock(int(f.Fd()), flag|syscall.LOCK_NB)
 		if err == nil {
 			return nil
 		} else if err != syscall.EWOULDBLOCK {
@@ -44,7 +48,7 @@ func funlock(f *os.File) error {
 func mmap(db *DB, sz int) error {
 	// Truncate and fsync to ensure file size metadata is flushed.
 	// https://github.com/boltdb/bolt/issues/284
-	if !db.NoGrowSync {
+	if !db.NoGrowSync && !db.readOnly {
 		if err := db.file.Truncate(int64(sz)); err != nil {
 			return fmt.Errorf("file resize error: %s", err)
 		}
@@ -59,6 +63,11 @@ func mmap(db *DB, sz int) error {
 		return err
 	}
 
+	// Advise the kernel that the mmap is accessed randomly.
+	if err := madvise(b, syscall.MADV_RANDOM); err != nil {
+		return fmt.Errorf("madvise: %s", err)
+	}
+
 	// Save the original byte slice and convert to a byte array pointer.
 	db.dataref = b
 	db.data = (*[maxMapSize]byte)(unsafe.Pointer(&b[0]))
@@ -80,3 +89,12 @@ func munmap(db *DB) error {
 	db.datasz = 0
 	return err
 }
+
+// NOTE: This function is copied from stdlib because it is not available on darwin.
+func madvise(b []byte, advice int) (err error) {
+	_, _, e1 := syscall.Syscall(syscall.SYS_MADVISE, uintptr(unsafe.Pointer(&b[0])), uintptr(len(b)), uintptr(advice))
+	if e1 != 0 {
+		err = e1
+	}
+	return
+}