On Fri, 9 Jan 2009, Brian Fundakowski Feldman wrote:
On Thu, Jan 08, 2009 at 10:44:20PM -0500, Daniel Eischen wrote:
On Thu, 8 Jan 2009, Brian Fundakowski Feldman wrote:
It appears that the post-fork hooks for malloc(3) are somewhat broken such that
when a threaded program forks, and then its child attempts to go threaded, it
deadlocks because it already appears to have locks held. I am not familiar
enough with the current libthr/libc/rtld-elf interaction that I've been able
to fix it myself, unfortunately.
There's really nothing to fix - according to POSIX you are only
allowed to call async-signal-safe functions in the child forked
from a threaded process. If you are trying to do anything other
than that, it may or may not work on FreeBSD, but it is not
guaranteed and is not portable.
The rationale is that what is the point of forking and creating
more threads, when you can just as easily create more threads in
the parent without forking? The only reason to fork from a threaded
process is to call one of the exec() functions.
Well, it worked until the last major set of changes to malloc. For me, the
point
was that I was able to have transparent background worker threads in any program
regardless of its architecture, using the standard pthread fork hooks. Could
you
point me to the POSIX section covering fork and threads? If it's really not
supposed to work then that's fine, but there's an awful lot of code there
dedicated
to support going threaded again after a fork.
I don't know if this link will work for you, but you can
start here:
http://www.opengroup.org/onlinepubs/009695399/nframe.html
"It is suggested that programs that use fork() call an exec
function very soon afterwards in the child process, thus
resetting all states. In the meantime, only a short list of
async-signal-safe library routines are promised to be available."
-- DE
--
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