Boost C++ Libraries: Ticket #4162: io_service can't be used correctly after fork().

artyomtnk@… — Sat, 01 May 2010 20:32:24 GMT

Any chances to get it fixed?

I'm developer of CppCMS framework. I use Boost.Asio as center event loop and support of prefork is one of central features of this framework. Now I'm quite stuck - I need either got this bug fixed, remove support of prefork or replace boost.asio with other library.

Thanks,

Artyom

type, milestone changed

chris_kohlhoff — Sat, 01 May 2010 22:33:54 GMT

type Bugs → Feature Requests
milestone Boost 1.43.0 → To Be Determined

Bind to port.
dup() acceptor descriptor.
Destroy io_service.
Prefork.
Create new io_service in child.
acceptor::assign()

artyomtnk@… — Sun, 02 May 2010 04:32:35 GMT

Bind to port.
dup() acceptor descriptor.
Destroy io_service.
Prefork.
Create new io_service in child.
acceptor::assign()

This was the first thing I thought and tried. But, I allow the library user to start some asynchronous actions before fork() at all. For example:

I allow him to create timers
I allow hit to post() some handlers to event queue so once the service is started they would be dispatched.

So the solution of creating new io_service is not quite fits my needs.

chris_kohlhoff — Sun, 02 May 2010 05:17:53 GMT

Sorry, but for now you'll simply have to start those asynchronous actions after the fork.

sephirok@… — Mon, 06 Sep 2010 14:13:12 GMT

It would be real nice to have boost.asio play nice with fork(), even after io_service creation or .run().

artyomtnk@… — Mon, 06 Sep 2010 14:28:16 GMT

To be honst, from my knowlege of boost.asio and my implementation of fork aware booster.aio for CppCMS I don't think this is quite simple feature to implement, few points:

Reactor should be created, first time only after fork, probably on call of io_service::run, otherwise, its file descriptor (for epoll/depoll/kqueue) would be shared between processes.,
Select interrupters should be created after fork as well as it my be shared between processes as well and lead to very bad bugs.

sephirok@… — Mon, 06 Sep 2010 23:49:28 GMT

I guess it wouldn't be possible to close the duplicate descriptors in the child and sort of "reinitialize" the io_service with a new eventfd aso.

Also what I haven't gotten working yet is just forking, letting the parent die and continuing as child - asio seems to hiccup.

chris_kohlhoff — Wed, 02 Mar 2011 08:28:04 GMT

(In [69467]) * Add support for the fork() system call. Programs that use fork must call

io_service.notify_fork() at the appropriate times. Two new examples have been added showing how to use this feature. Refs #3238, #4162.

Clean up the handling of errors reported by the close() system call. In particular, assume that most operating systems won't have close() fail with EWOULDBLOCK, but if it does then set blocking mode and restart the call. If any other error occurs we assume the descriptor is closed. Refs #3307.

EV_ONESHOT seems to cause problems on some versions of Mac OS X, with the io_service destructor getting stuck inside the close() system call. Use EV_CLEAR instead. Refs #5021.

Include function name in exception what() messages.

Fix insufficient initialisers warning with MinGW.

Make the shutdown_service() member functions private.

Add archetypes for testing socket option functions.

Add missing lock in signal_set_service::cancel().

Fix copy/paste error in SignalHandler example.

The signal header needs to be included in signal_set_service.hpp so that we can use constants like NSIG and SIGRTMAX.

Don't use Boost.Thread's convenience header. Use the header file that is specifically for the boost::thread class instead.

status changed; resolution set

chris_kohlhoff — Mon, 06 Jun 2011 01:44:19 GMT

status new → closed
resolution → fixed

Applied to release branch in [72428].