closes #3762

[arvados.git] / services / keepstore / volume_unix.go

diff --git a/services/keepstore/volume_unix.go b/services/keepstore/volume_unix.go
index 4db2a5338400af7aa8c31089df63cf8cf71c502e..84877c003409a5af12df2c6fe154102c528044df 100644 (file)
--- a/services/keepstore/volume_unix.go
+++ b/services/keepstore/volume_unix.go
@@ -255,6 +255,14 @@ func (v *UnixVolume) Index(prefix string) (output string) {
 }
 
 func (v *UnixVolume) Delete(loc string) error {
+       // Touch() must be called before calling Write() on a block.  Touch()
+       // also uses lockfile().  This avoids a race condition between Write()
+       // and Delete() because either (a) the file will be deleted and Touch()
+       // will signal to the caller that the file is not present (and needs to
+       // be re-written), or (b) Touch() will update the file's timestamp and
+       // Delete() will read the correct up-to-date timestamp and choose not to
+       // delete the file.
+
        p := v.blockPath(loc)
        f, err := os.OpenFile(p, os.O_RDWR|os.O_APPEND, 0644)
        if err != nil {