Date: Mon, 23 Jan 2006 23:32:28 -0500 (EST) From: Daniel Eischen <deischen@freebsd.org> To: Peter Jeremy <PeterJeremy@optushome.com.au> Cc: freebsd-current@freebsd.org Subject: Re: kernel thread as real threads.. Message-ID: <Pine.GSO.4.43.0601232319140.20562-100000@sea.ntplx.net> In-Reply-To: <20060124020137.GW25397@cirb503493.alcatel.com.au>
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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. -- DE
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