[lxc-devel] [PATCH] Use pthread_atfork() to unlock mutexes after fork()

[Stéphane Graber]

On Thu, Jan 02, 2014 at 08:59:10AM -0600, Serge Hallyn wrote:
> Quoting Stéphane Graber (stgraber at ubuntu.com):
> > On Wed, Jan 01, 2014 at 11:37:32PM -0600, Serge Hallyn wrote:
> > > Quoting Stéphane Graber (stgraber at ubuntu.com):
> > > > This patch caused a build failure on Android:
> > > > 
> > > > arm-linux-androideabi-gcc --sysroot=/tmp/android-build-scripts/android-ndk-r9b/platforms/android-9/arch-arm/ -DHAVE_CONFIG_H -I. -I../../src    -fPIC -DPIC -I../../src -DLXCROOTFSMOUNT=\"/data/lxc/lxc/lib/lxc/rootfs\" -DLXCPATH=\"/data/lxc/lxc/var/lib/lxc\" -DLXC_GLOBAL_CONF=\"/data/lxc/lxc/etc/lxc/lxc.conf\" -DLXCINITDIR=\"/data/lxc/lxc/libexec\" -DLXCTEMPLATEDIR=\"/data/lxc/lxc/share/lxc/templates\" -DLOGPATH=\"/data/lxc/lxc/var/log/lxc\" -DLXC_DEFAULT_CONFIG=\"/data/lxc/lxc/etc/lxc/default.conf\" -DLXClxclock.c: In function 'process_lock_setup_atfork':
> > > > lxclock.c:332:2: error: implicit declaration of function 'pthread_atfork' [-Werror=implicit-function-declaration]
> > > >   pthread_atfork(process_lock, process_unlock, process_unlock);
> > > 
> > > Hm,  according to
> > > http://stackoverflow.com/questions/12370970/undefined-reference-to-pthread-atfork-while-i-was-trying-to-port-libpcsclite-t
> > > perhaps all we need is to declare the fn before its use.  Do you
> > > have a local bionic compiler handy to test that on?
> > 
> > Not having much luck with that... this just turned it into:
> > 
> > liblxc.so: error: undefined reference to 'pthread_atfork'
> > 
> > pthread on bionic is part of the C library so no extra linker flags
> > should be needed to make this work...
> 
> Hm.  So we can either (a) keep looking for a way to make it work in
> bionic, (b) give in and switch all uses of fork() to lxc_fork() to
> do our own atfork hook, or (c) detect at configure.ac whether we have
> pthread_atfork(), and if not then just don't do it.

I think doing (c) would be the easiest here and would also mean that
whenever pthread_atfork actually shows up in bionic (assuming the
configure.ac detection code doesn't already detect it as present...),
things will just work.

It may be worth adding an entry to the configure.ac config overview part
to indicate threading support so it's clear to anyone building on bionic
that they shouldn't expect this to be working.

-- 
Stéphane Graber
Ubuntu developer
http://www.ubuntu.com
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