[asio-users] is it possible to use asio in level-triggered mode?

[Daniel H. <dan...@gm...>]

I see by inspecting the source code that asio uses edge-triggered epoll on
linux. I also see some history from circa 2009-2010 where this design
decision was evaluated for performance reasons. It makes sense to me.
However, I cannot seem to make edge-triggered mode compatible with libcurl
if libcurl is used in the "event-driven multi" mode where the app handles
all notifications and interacts with curl entirely through callbacks.
Although you can accomplish identical goals with both edge-triggered and
level-triggered designs, the division of responsibilities between libcurl
and the application that uses it makes this quite difficult in my scenario.
See this post on the libcurl mailing list:
http://curl.haxx.se/mail/lib-2015-04/0104.html

There is a sample piece of code that demonstrates an integration between
asio and libcurl in the libcurl codebase, but it no longer works. I was
able to confirm that it was written before this design change to asio
propagated, and that the breakage traces to this evolution of asio.

I am wondering if the asio team would accept a patch that would allow the
edge-vs-level-triggered decision to be configurable (e.g., as an arg to the
ctor of an io_service object), so that level-triggered usage becomes
possible again. I realize that this would decrease asio performance to some
extent, but would that do a lot of violence to other internals or other
design imperatives?

--Daniel