Date: Mon, 23 Jan 2006 21:38:56 -0800 From: Julian Elischer <julian@elischer.org> To: Daniel Eischen <deischen@freebsd.org> Cc: Peter Jeremy <PeterJeremy@optushome.com.au>, freebsd-current@freebsd.org Subject: Re: kernel thread as real threads.. Message-ID: <43D5BD70.6080503@elischer.org> In-Reply-To: <Pine.GSO.4.43.0601232319140.20562-100000@sea.ntplx.net> References: <Pine.GSO.4.43.0601232319140.20562-100000@sea.ntplx.net>
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Daniel Eischen wrote: >On Tue, 24 Jan 2006, Peter Jeremy wrote: > > > >>On Mon, 2006-Jan-23 20:38:46 -0500, Daniel Eischen wrote: >> >> >>>On Tue, 24 Jan 2006, Peter Jeremy wrote: >>> >>> >>> >>>>On Mon, 2006-Jan-23 19:59:02 -0500, Daniel Eischen wrote: >>>> >>>> >>>>>POSIX specifies that only 1 thread (the forking thread) is present >>>>>after a fork. >>>>> >>>>> >>>>Just to clarify, I presume you are talking about only one thread >>>>existing in the child process and the parent's threads still exist as >>>>they did before the fork(). If fork() arbitrarily killed all the >>>>threads in the parent process, that would be a real PITA. >>>> >>>> >>>Correct, I assumed we were talking about the child process. >>> >>> >>My understanding of Robert's issue was the case where a parent has >>multiple threads, one thread does a fork() whilst the remaining >>threads are not blocked. If the remaining threads are executing >>whilst fork() is copying the process address space, then the child >>will could inherit a confused (partially indeterminate) copy of the >>parent's address space, depending on what the other threads have >>been doing. >> >> > >I think that's OK. The only thing that is guaranteed safe (in the >child) after a fork from a multi-threaded process are the >async-signal-safe functions. If a process has aio active, >it shouldn't assume anything about the childs state after a >fork. I think it's only important that the forking thread >continues on normally in the child. OTOH, if there is a >possibility of some inconsistent kernel state that will affect >the child if it calls any of the async-signal-safe functions >or one of the exec() functions, that should be avoided. > > It's not a case of kernel state so much as the state of user space. Of course there is some course kernel state involved, such as if one thread does a fork while the other is mmaping pages or setting signals.
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