X-Git-Url: http://git.vanrenterghem.biz/git.ikiwiki.info.git/blobdiff_plain/506bcbac0420a46997ad531961d543e62c011513..227107b21864dedb40995875c6a68c1a2a665f9a:/doc/plugins/write/external.mdwn

diff --git a/doc/plugins/write/external.mdwn b/doc/plugins/write/external.mdwn
index 735f7a20e..a1a3811dc 100644
--- a/doc/plugins/write/external.mdwn
+++ b/doc/plugins/write/external.mdwn
@@ -8,6 +8,12 @@ written in perl, but is intended to be an example of how to write an
 external plugin in your favorite programming language. Wow us at how much
 easier you can do the same thing in your favorite language. ;-)
 
+There's now a second external plugin, the [[rst]] plugin, written in
+python. (Could someone convert it into a python library that can be used by
+other plugins?)
+
+[[toc ]]
+
 ## How external plugins use XML RPC
 
 While XML RPC is typically used over http, ikiwiki doesn't do that.
@@ -43,6 +49,11 @@ to access any such global hash. To get the "url" configuration value,
 call `getvar("config", "url")`. To set it, call 
 `setvar("config", "url", "http://example.com/)`.
 
+The `%pagestate` is a special hash with a more complex format. To access
+it, external plugins can use the `getstate` and `setstate` RPCs. To access
+stored state, call `getstate("page", "id", "key")`, and to store state,
+call `setstate("page", "id", "key", "value")`.
+
 ## Notes on function parameters
 
 The [[plugin_interface_documentation|write]] talks about functions that take
@@ -78,11 +89,45 @@ example, make an RPC call to `inject`. Pass it named parameters "name" and
 "Ikiwiki::rcs_update" and "call" is the RPC call ikiwiki will make whenever
 that function is run.
 
+If the RPC call is memoizable, you can also pass a "memoize" parameter, set
+to 1.
+
 ## Limitations of XML RPC
 
 Since XML RPC can't pass around references to objects, it can't be used
 with functions that take or return such references. That means you can't
-use XML RPC for `cgi` or `formbuilder` hooks (which are passed CGI and
+100% use XML RPC for `cgi` or `formbuilder` hooks (which are passed CGI and
 FormBuilder perl objects), or use it to call `template()` (which returns a
 perl HTML::Template object).
 
+Also. the `getopt` hook doesn't work, as ARGV is not available to the external
+plugin.
+
+## Performance issues
+
+Since each external plugin is a separate process, when ikiwiki is
+configured to use lots of external plugins, it will start up slower, and
+use more resources. One or two should not be a problem though.
+
+There is some overhead in using XML RPC for function calls. Most plugins
+should find it to be pretty minimal though. In one benchmark, ikiwiki was
+able to perform 10000 simple XML RPC calls in 11 seconds -- 900 per second.
+
+Using external plugins for hooks such as `sanitize` and `format`, which
+pass around entire pages, and are run for each page rendered, will cause
+more XML RPC overhead than usual, due to the larger number of calls, and the
+large quantity of data conversion going on. In contrast, `preprocess` hooks
+are called generally rarely, and pass around minimal data.
+
+External plugins should avoid making RPC calls unnecessarily (ie, in a loop).
+Memoizing the results of appropriate RPC calls is one good way to minimise the
+number of calls.
+
+Injecting a replacement for a commonly called ikiwiki function
+could result in a lot more RPC calls than expected and slow
+eveything down. `pagetitle`, for instance, is called about 100 times
+per page build. Whenever possible, you should tell ikiwiki to memoize
+injected functions.
+
+In general, use common sense, and your external plugin will probably
+perform ok.