mirrors/git-annex
2
0
Fork 0
Code Issues Pull requests Projects Releases Packages 1 Wiki Activity Actions

followup

Browse source
This commit is contained in:
Joey Hess 2018-11-19 18:11:43 -04:00
parent e053df9451
commit 9c0cece35a
No known key found for this signature in database
GPG key ID: DB12DB0FF05F8F38
2 changed files with 34 additions and 2 deletions
Download patch file Download diff file Expand all files Collapse all files

30
doc/bugs/multiple_ssh_prompts__44___and_thread_blocked_indefinitely_in_an___63____63____63___transaction/comment_33_3338f896a983292bef576dcd369bba5a._comment Normal file
View file

@ -0,0 +1,30 @@
[[!comment format=mdwn
username="joey"
subject="""comment 33"""
date="2018-11-19T21:57:13Z"
content="""
Interesting that one side of the deadlock is a MVar and the other side is STM:
MVar deadlock detected CallStack (from HasCallStack):
debugLocks, called at Messages.hs:265:12 in main:Messages
STM deadlock detected CallStack (from HasCallStack):
debugLocks, called at Messages.hs:265:12 in main:Messages
This seems consistent with a single call of `waitDisplayChange` being involved.
That's the STM side. The MVar side is the `takeMVar` call in `prompt`.
So somehow `waitDisplayChange` is blocking and of course the `takeMVar`
also blocks waiting for it. But with only a single caller to `waitDisplayChange`,
my bug fix in concurrent-output can't have been the actual fix. It has to
block with a single caller.
Oh, what if `waitDisplayChange` is called when there are no display changes
pending, because there are no console regions being displayed?
I think it would still block then!
In a bench test I've at least verified it hangs in that situation, though I have not
triggered ghc's deadlock detection. Which is good enough for me, I know
I need to fix this problem in concurrent-output, and also it seems my earlier
fix to git-annex is enough to avoid triggering the underlying bug; git-annex
won't need to depend on the fixed concurrent-output.
"""]]