Forum OpenACS Development: Re: ANNOUNCE: NaviServer 4.99.8 available

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Posted by Gustaf Neumann on
Hi Steffen,

With recent versions of NaviServer, most of the usages of bg-delivery can be replaced by "ns_writer submitfile ..." when writer-threads are in use (look for use_writerThread in [1]). The writer threads are roughly the equivalence of the bgdelivery thread, but implemented in C, not relying on select(), are lightweight in memory use and fast (using the common io-machinery of NaviServer). For the introduction to the async support in NaviServer, see section "2.3. Asynchronous Architecture" in [2].

In fact, when one is using a recent version of xotcl-core, ad_returnfile_background uses automatically the writer threads, no application code changes are needed. we use this since a while on our production systems an on openacs.org.

Actually, the only place were we are still using - and that might be the source of your interest - is the h264 streaming code. It should be actually not hard to replace there the tcl/io (e.g. replace "puts -nonewline $channel ..." by "ns_connchan write $channel ...", use "ns_connchan callback ...", etc.). This has as well the advantage that it will work without changes with tls. When one wants to copy the fd from a channel, this would defeat this purpose. So far, i had no time to look into the details to implement h264 delivery via ns_connchan.

To see ns_connchan in action, look at the WebSocket code in [3].

-g

[1] http://openacs.org/xotcl/show-object?show_methods=2&show_source=1&object=bgdelivery
[2] https://next-scripting.org/xowiki/docs/misc/naviserver-connthreadqueue/index1
[3] https://bitbucket.org/naviserver/websocket/src/c9da8e104075ed8bb9a1d3e6a244f99fd730f0fc/websocket-procs.tcl?at=default

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Posted by Steffen Tiedemann Christensen on
Good to know! I really need to look into the project of switching our core over to to NaviServer. It is complicated by the fact that we use a fairly old and fairly modified version of OpenACS.

We use the h264 delivery mechanism less and less these days ourselves, but we never actually used ad_background_returnfile for the purspose. Instead we've simply got a tcl thread handling the reading and writing. HTML5 and byte ranges have decreased the use of this drastically though.

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Posted by Gustaf Neumann on
The same with us (that's why a rewrite of h264 is not top prio). i just looked up our figures for video deliveries for our production site: factor h264/html5 = 1/9, with peaks on htm5: 5.500 per hour.

Concerning ad_returnfile_background: it has the same interface like ns_returnfile. The changes for NaviServer in OpenACS are mostly due to using features of NaviServer not available in aolserver. If you get a recent version of OpenACS (e.g. the tar file), just grep for NaviServer, these should be pretty easy applicable for every OpenACS mutant.