Check if enough FDs are free, instead counting the total free FDs.

[fujitatomoya]

fix #1927,

requirement seems that there is enough free file descriptors or not, that is it.
so no need to count the number of free file descriptors.

Signed-off-by: Tomoya.Fujita tomoya.fujita825@gmail.com

[flixr]

You are still counting the number of free FDs...
I don't see how this could help at all... or what am I missing?

[fujitatomoya]

@flixr

You are still counting the number of free FDs...

actually it is, once it hits the enough number, it returns. I guess that this could be faster in most cases against checking all.

[flixr]

True, my oversight... and I guess since it polls fds with increasing number it should first go through all used fds, then unused ones (at which point it exits early enough free ones are found).

[wenbin1989]

thanks @fujitatomoya
it works fine, the connections init latency reduces a lot.
but I still have concerns about the std::vector<struct pollfd> pollfds vector.
it resizes to max_files at

ros_comm/utilities/xmlrpcpp/src/XmlRpcServer.cpp

Line 45 in 87b2baf

pollfds.resize(max_files);

which is 1048576 inside docker container. it takes extra 8MB memory, I think we don't need allocate the total FDs there as well?

[fujitatomoya]

@wenbin1989

thanks for checking, appreciate it.

std::vector pollfds

nice catch, to be honest, i did miss it. thanks!

but i do not have any idea to reduce it. since we cannot know how many/what events in poll() returns, i guess that we have to keep the maximum.

[harlowja]

Possible to allocate and check pollfds in chunks of smaller sizes?

[fujitatomoya]

Possible to allocate and check pollfds in chunks of smaller sizes?

I don't think so,

we do not know which file descriptor returns with POLLNVAL, actually that is exactly what we are trying to get here. so i believe that we need to scan with max index for pollfds, then once hits the requirement, return right away.

[fujitatomoya]

@dirk-thomas

do we have a go on this to merge?

[dirk-thomas]

Thanks for the patch.

[wenbin1989]

thanks! @dirk-thomas can we update the package version?

[dirk-thomas]

can we update the package version?

Since patch releases of the ros_comm are fairly expensive in terms of resources to rebuild almost full ROS distros as well as bandwidth for every user downloading new .debs they happen whenever a significant enough amount of changes have accumulated. So it will likely be some time (I would guess a couple of weeks) until a new patch release will be available in Noetic and Melodic.