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Differential D9533

persistent-nodemap: properly ignore non-existent `.nd` data file
ClosedPublic

Authored by SimonSapin on Dec 7 2020, 12:53 PM.

Details

Reviewers
Alphare
pulkit
Group Reviewers
hg-reviewers
Commits
rHG8ff2d8359d0f: persistent-nodemap: properly ignore non-existent `.nd` data file
Summary

This code was meant to handle the case of a nodemap docket file
pointing to a nodemap data file that doesn’t exist (anymore),
but most likely caused an UnboundLocalError exception instead
when data was used on the next line without being defined.

This case is theoretically possible with a race condition
between two hg processes, but is hard to reproduce or test:

  • Process A reads a docket file and finds a UID in it that points to a given data file name.
  • Process B decides that this same data file needs compacting. It writes a new one with a different UID, overwrites the docket file, then removes the old data file.
  • Only then process A tries to a open a file that doesn’t exist anymore.

Diff Detail

Repository
rHG Mercurial
Lint
Automatic diff as part of commit; lint not applicable.
Unit
Automatic diff as part of commit; unit tests not applicable.

Event Timeline

SimonSapin created this revision.Dec 7 2020, 12:53 PM
Alphare accepted this revision.Dec 7 2020, 2:43 PM
pulkit accepted this revision.Dec 10 2020, 3:46 AM
This revision is now accepted and ready to land.Dec 10 2020, 3:46 AM

Revision Contents
Changeset List

PathPackages
Mmercurial/revlogutils/nodemap.py (4 lines)

Diff 24160

mercurial/revlogutils/nodemap.py

use_mmap = revlog.opener.options.get(b"persistent-nodemap.mmap") use_mmap = revlog.opener.options.get(b"persistent-nodemap.mmap")
try: try:
with revlog.opener(filename) as fd: with revlog.opener(filename) as fd:
if use_mmap: if use_mmap:
data = util.buffer(util.mmapread(fd, data_length)) data = util.buffer(util.mmapread(fd, data_length))
else: else:
data = fd.read(data_length) data = fd.read(data_length)
except OSError as e: except OSError as e:
if e.errno != errno.ENOENT: if e.errno == errno.ENOENT:
return None
else:
raise raise
if len(data) < data_length: if len(data) < data_length:
return None return None
return docket, data return docket, data
def setup_persistent_nodemap(tr, revlog): def setup_persistent_nodemap(tr, revlog):
"""Install whatever is needed transaction side to persist a nodemap on disk """Install whatever is needed transaction side to persist a nodemap on disk