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Race condition on history file with multiple REPLs #1634
Description
via @substack
<substack> found another repl history bug, if you have 2 repls open at once it doesn't lock the file
<substack> but a bit hard to reproduce since they've got to be writing at the same time
<substack> but I already ran into it just doing normal things with 2 repls open at once
Activity
chrisdickinson commentedon May 7, 2015
Looking into this. I see two possible solutions. If anyone has a better idea, please let me know!
bnoordhuis commentedon May 7, 2015
Option 1 can work as long as the files are on the same mount. Option 2 has portability issues and is unreliable with NFS.
rvagg commentedon May 7, 2015
can we see what bash does and copy that?
chrisdickinson commentedon May 7, 2015
What about mmap'ing the file & setting a semaphore byte? This might be a bit too heavyweight of a solution, since it would require mmap support be added to libuv.
ivan commentedon May 13, 2015
Just for the record: this happens so frequently not because of racing writes but because both REPLs have the history file open in 'w' mode, one REPL exits and writes some history, and the other REPL exits and writes a shorter history, leaving behind some trailing bytes from the longer history.
evanlucas commentedon Feb 2, 2016
It seems like since we moved away from using json, this is no longer prevalent. Do we still need to implement some sort of locking to prevent corruption?
Fishrock123 commentedon Mar 16, 2016
Locking would probably be desirable if someone wants to take it up. It would be pretty complex though.
lance commentedon May 25, 2016
I started working on a locking implementation for this, but I'm not totally clear on the desired behavior. If multiple REPLs are open should history be interleaved? Or is it last-write-wins behavior?
Fishrock123 commentedon May 25, 2016
@lance either or. I'd prefer interleaved. Most terminals do last-write-is-latest-history.
lance commentedon Aug 3, 2016
Removed
good-first-contributionlabel as I don't think this is the case. At least not if #7005 is any indication.Trott commentedon Jul 9, 2017
This issue has been inactive for sufficiently long that it seems like perhaps it should be closed. Feel free to re-open (or leave a comment requesting that it be re-opened) if you disagree. I'm just tidying up and not acting on a super-strong opinion or anything like that.