#4449: GHC 7 can't do IO when demonized
----------------------------+-----------------------------------------------
Reporter: kazu-yamamoto | Owner: adept
Type: bug | Status: new
Priority: normal | Milestone: 7.0.2
Component: Compiler | Version: 7.1
Resolution: | Keywords: forkProcess
Testcase: | Blockedby:
Difficulty: | Os: MacOS X
Blocking: | Architecture: x86
Failure: None/Unknown |
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Comment(by adept):
OK. More info. Now that I understand the `mkWeakIORef` properly (it just
adds a finalizer to the `IORef`) I should rephrase the description of the
root cause.
It all happens like this. Parent process creates IO manager, and finalizer
is added to the `state` argument inside `newWith`. Then this IORef plus
finalized are carried on to the child process on `fork()`. Event if child
process explicitly closes the inherited IO manager with `ioManagerDie()`,
there is no guarantee that GC will come to collect the remains of the old
IO manger befor the new one is created.
Thus, finalizer for the inherited IO manger could be run _after_ new one
is created, and there is no easy way to force it run sooner. Since
`Controls` of the both managers refer to the same file descriptors, we
have errors (double close) when they are finally run, plus finalizers of
the inherited manager close control pipes of the new manager.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/4449#comment:39>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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