open the lock file for writing

Author: chlowell

extensions/internal/flock/flock.go

@@ -19,7 +19,6 @@ package flock
 import (
 	"context"
 	"os"
-	"runtime"
 	"sync"
 	"time"
 )
@@ -120,24 +119,11 @@ func tryCtx(ctx context.Context, fn func() (bool, error), retryDelay time.Durati
 }
 
 func (f *Flock) setFh() error {
-	// open a new os.File instance
-	// create it if it doesn't exist, and open the file read-only.
-	flags := os.O_CREATE
-	if runtime.GOOS == "aix" {
-		// AIX cannot preform write-lock (ie exclusive) on a
-		// read-only file.
-		flags |= os.O_RDWR
-	} else {
-		flags |= os.O_RDONLY
+	fh, err := os.OpenFile(f.path, os.O_CREATE|os.O_RDWR, os.FileMode(0600))
+	if err == nil {
+		f.fh = fh
 	}
-	fh, err := os.OpenFile(f.path, flags, os.FileMode(0600))
-	if err != nil {
-		return err
-	}
-
-	// set the filehandle on the struct
-	f.fh = fh
-	return nil
+	return err
 }
 
 // ensure the file handle is closed if no lock is held

extensions/internal/lock/lock.go

@@ -66,7 +66,10 @@ func (l *Lock) Lock(ctx context.Context) error {
 				return err
 			}
 		} else if locked {
-			_, _ = l.f.Fh().WriteString(fmt.Sprintf("{%d} {%s}", os.Getpid(), os.Args[0]))
+			if fh := l.f.Fh(); fh != nil {
+				s := fmt.Sprintf("{%d} {%s}", os.Getpid(), os.Args[0])
+				_, _ = fh.WriteString(s)
+			}
 			return nil
 		}
 	}

extensions/internal/lock/lock_test.go

@@ -4,8 +4,10 @@
 package lock
 
 import (
+	"bytes"
 	"context"
 	"errors"
+	"io"
 	"os"
 	"path/filepath"
 	"runtime"
@@ -49,11 +51,40 @@ func TestCreatesAndRemovesFile(t *testing.T) {
 	require.NoError(t, err)
 	require.FileExists(t, p, "Lock didn't create the file")
 
+	buf := bytes.NewBuffer(nil)
+	_, err = io.Copy(buf, lock.f.Fh())
+	require.NoError(t, err)
+	require.NotEmpty(t, buf, "Lock didn't write debug info to the locked file")
+
 	err = lock.Unlock()
 	require.NoError(t, err)
 	require.NoFileExists(t, p, "Unlock didn't remove the file")
 }
 
+func TestFileExists(t *testing.T) {
+	p := filepath.Join(t.TempDir(), t.Name())
+	f, err := os.Create(p)
+	require.NoError(t, err)
+	data := "stuff"
+	_, err = f.WriteString(data)
+	require.NoError(t, err)
+	require.NoError(t, f.Close())
+
+	// Lock should succeed when the file exists but isn't locked
+	lock, err := New(p, 0)
+	require.NoError(t, err)
+	err = lock.Lock(ctx)
+	require.NoError(t, err)
+
+	buf := bytes.NewBuffer(nil)
+	_, err = io.Copy(buf, lock.f.Fh())
+	require.NoError(t, err)
+	require.NotEqual(t, data, buf, "Lock didn't write debug info to the locked file")
+
+	require.NoError(t, lock.Unlock())
+	require.NoFileExists(t, p, "Unlock didn't remove the file")
+}
+
 func TestLockError(t *testing.T) {
 	p := filepath.Join(t.TempDir(), t.Name())
 	lock, err := New(p, 0)