diff --git a/pkg/blobstore/Makefile b/pkg/blobstore/Makefile
index db07d2f..3eba753 100644
--- a/pkg/blobstore/Makefile
+++ b/pkg/blobstore/Makefile
@@ -6,9 +6,9 @@ GOFILES = \
 	blobreader.go
 
 ifeq ($(GOOS),windows)
-GOFILES += pid_windows.go
+GOFILES += lock_windows.go
 else
-GOFILES += pid_unix.go
+GOFILES += lock_unix.go
 endif
 
 include $(GOROOT)/src/Make.pkg
diff --git a/pkg/blobstore/lock_unix.go b/pkg/blobstore/lock_unix.go
new file mode 100644
index 0000000..32ce0d2
--- /dev/null
+++ b/pkg/blobstore/lock_unix.go
@@ -0,0 +1,73 @@
+// Copyright (c) 2011 The Grumble Authors
+// The use of this source code is goverened by a BSD-style
+// license that can be found in the LICENSE-file.
+
+package blobstore
+
+import (
+	"os"
+	"path/filepath"
+	"io/ioutil"
+	"strconv"
+	"syscall"
+)
+
+// Acquire lockfile at path.
+func AcquireLockFile(path string) os.Error {
+	dir, fn := filepath.Split(path)
+	lockfn := filepath.Join(dir, fn)
+
+	lockfile, err := os.OpenFile(lockfn, os.O_WRONLY|os.O_CREATE|os.O_EXCL, 0600)
+	if e, ok := err.(*os.PathError); ok && e.Error == os.EEXIST {
+		content, err := ioutil.ReadFile(lockfn)
+		if err != nil {
+			return err
+		}
+
+		pid, err := strconv.Atoi(string(content))
+		if err == nil {
+			if syscall.Kill(pid, 0) == 0 {
+				return ErrLocked
+			}
+		}
+
+		lockfile, err = ioutil.TempFile(dir, "lock")
+		if err != nil {
+			return err
+		}
+
+		_, err = lockfile.WriteString(strconv.Itoa(syscall.Getpid()))
+		if err != nil {
+			lockfile.Close()
+			return ErrLockAcquirement
+		}
+
+		curfn := lockfile.Name()
+
+		err = lockfile.Close()
+		if err != nil {
+			return err
+		}
+
+		err = os.Rename(curfn, lockfn)
+		if err != nil {
+			os.Remove(curfn)
+			return ErrLockAcquirement
+		}
+	} else if err != nil {
+		return err
+	} else {
+		_, err = lockfile.WriteString(strconv.Itoa(syscall.Getpid()))
+		if err != nil {
+			return err
+		}
+		lockfile.Close()
+	}
+
+	return nil
+}
+
+// Release lockfile at path.
+func ReleaseLockFile(path string) os.Error {
+	return os.Remove(path)
+}
diff --git a/pkg/blobstore/lock_windows.go b/pkg/blobstore/lock_windows.go
new file mode 100644
index 0000000..028d790
--- /dev/null
+++ b/pkg/blobstore/lock_windows.go
@@ -0,0 +1,29 @@
+// Copyright (c) 2011 The Grumble Authors
+// The use of this source code is goverened by a BSD-style
+// license that can be found in the LICENSE-file.
+
+package blobstore
+
+import (
+	"os"
+	"syscall"
+)
+
+const (
+	FILE_FLAG_DELETE_ON_CLOSE = 0x04000000
+)
+
+// Acquire a lockfile at path.
+func AcquireLockFile(path string) os.Error {
+	handle, _ := syscall.CreateFile(syscall.StringToUTF16Ptr(path), syscall.GENERIC_WRITE, 0, nil, syscall.CREATE_ALWAYS, FILE_FLAG_DELETE_ON_CLOSE, 0)
+	if handle < 0 {
+		return ErrLocked
+	}
+	return nil
+}
+
+// Release the lockfile at path.
+func ReleaseLockFile(path string) os.Error {
+	// No-op because we use FLAG_DELETE_ON_CLOSE.
+	return nil
+}
diff --git a/pkg/blobstore/pid_unix.go b/pkg/blobstore/pid_unix.go
deleted file mode 100644
index a4fcc53..0000000
--- a/pkg/blobstore/pid_unix.go
+++ /dev/null
@@ -1,17 +0,0 @@
-// Copyright (c) 2011 The Grumble Authors
-// The use of this source code is goverened by a BSD-style
-// license that can be found in the LICENSE-file.
-
-package blobstore
-
-import (
-	"syscall"
-)
-
-func getPid() uint64 {
-	return uint64(syscall.Getpid())
-}
-
-func pidRunning(pid uint64) bool {
-	return syscall.Kill(int(pid), 0) == 0
-}
diff --git a/pkg/blobstore/pid_windows.go b/pkg/blobstore/pid_windows.go
deleted file mode 100644
index 043010f..0000000
--- a/pkg/blobstore/pid_windows.go
+++ /dev/null
@@ -1,20 +0,0 @@
-// Copyright (c) 2011 The Grumble Authors
-// The use of this source code is goverened by a BSD-style
-// license that can be found in the LICENSE-file.
-
-package blobstore
-
-import (
-	"syscall"
-)
-
-func getPid() uint64 {
-	handle, _ := syscall.GetCurrentProcess()
-	return uint64(handle)
-}
-
-func pidRunning(pid uint64) bool {
-	var status uint32
-	syscall.GetExitCodeProcess(uint32(pid), &status)
-	return status == 259 // STILL_ACTIVE 
-}