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make safeCommand stop the process if the thread gets killed

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And a comment on a todo item that this commit is perhaps the start of
solving.
This commit is contained in:
Joey Hess 2020-06-03 12:52:11 -04:00
parent 156e728b56
commit e1fc4f7594
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2 changed files with 36 additions and 3 deletions
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6
Utility/SafeCommand.hs
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@ -81,9 +81,9 @@ safeSystem :: FilePath -> [CommandParam] -> IO ExitCode
safeSystem command params = safeSystem' command params id
safeSystem' :: FilePath -> [CommandParam] -> (CreateProcess -> CreateProcess) -> IO ExitCode
safeSystem' command params mkprocess = do
(_, _, _, pid) <- createProcess p
waitForProcess pid
safeSystem' command params mkprocess =
withCreateProcess p $ \_ _ _ pid ->
waitForProcess pid
where
p = mkprocess $ proc command (toCommand params)

33
doc/todo/more_extensive_retries_to_mask_transient_failures/comment_11_9c289d93f49ff59fddd214d51356b1f9._comment Normal file
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@ -0,0 +1,33 @@
[[!comment format=mdwn
username="joey"
subject="""comment 11"""
date="2020-06-03T16:10:44Z"
content="""
Ah, withCreateProcess is the bracketing version that's needed, it uses
cleanupProcess. And readProcess already uses it. It was easy to make
safeSystem use it, so I've already done so. Other calls to waitForProcess
probably indicate places that need to use it.
Reading its code, I found a couple of gotchas:
* If another thread has a Handle for the process, and are "holding the
handle lock", and lead to deadlock when cleanupProcess tries to close
them. This would seem to involve something that uses withHandle and
blocks for some reason, maybe just reading/writing to the Handle?
I've tried a few things like passing the handle into another thread
started with async, that uses hGetLine, but could not produce a deadlock,
the process was always killed anyway.
Seems like using withAsync would help make sure any thread the handle
is passed to does get killed.
* It sends SIGTERM, which doesn't necessarily kill every process. So
withCreateProcess might exit cleanly but leave the process hanging
around.
I doubt this is really a problem in anything git-annex runs.
And if some program did ignore SIGTERM, wouldn't ctrl-c of git-annex
also leave that running? Never seen that happen which confirms my feeling
it's likely not a problem in something git-annex runs, but you never
know.
"""]]