samba-mirror/lib/tevent/doc/tevent_context.dox

/**
@page tevent_context Chapter 1: Tevent context

@section context Tevent context

Tevent context is an essential logical unit of tevent library. For working with
events at least one such context has to be created - allocated, initialized.
Then, events which are meant to be caught and handled have to be registered
within this specific context. Reason for subordinating events to a tevent
context structure rises from the fact that several context can be created and
each of them is processed at different time. So, there can be 1 context
containing just file descriptor events, another one taking care of signal and
time events and the third one which keeps information about the rest.

Tevent loops are the part of the library which represents the mechanism where
noticing events and triggering handlers actually happens. They accept just one
argument - tevent context structure. Therefore if theoretically an infinity
loop (tevent_loop_wait) was called, only those arguments which belong to the
passed tevent context structure can be caught and invoked within this call.
Although some more signal events were registered (but within some other
context) they will not be noticed.

@subsection Example

First lines which handle <code>mem_ctx</code> belong to talloc library
knowledge but because of the fact that tevent uses the talloc library for its
mechanisms it is necessary to understand a bit talloc as well. For more
information about working with talloc, please visit <a
href="http://talloc.samba.org/">talloc website</a> where tutorial and
documentation are located.

Tevent context structure <code>*event_ctx</code> represents the unit which will
further contain information about registered events. It is created via calling
tevent_context_init().

@code
TALLOC_CTX *mem_ctx = talloc_new(NULL);
if (mem_ctx == NULL) {
    // error handling
}

struct tevent_context *ev_ctx = tevent_context_init(mem_ctx);
if(ev_ctx == NULL) {
    // error handling
}
@endcode

Tevent context has a structure containing lots of information. It include lists
of all events which are divided according their type and are in order showing
the sequence as they came.

@image html tevent_context_stucture.png

In addition to the lists shown in the diagram, the tevent context also contains
many other data (e.g. information about the available system mechanism for
triggering callbacks).

@section tevent_loops Tevent loops

Tevent loops are the dispatcher for events. They catch them and trigger the
handlers. In the case of longer processes, the program spends most of its time
at this point waiting for events, invoking handlers and waiting for another
event again. There are 2 types of loop available for use in tevent library:

<ul>
<li>int tevent_loop_wait()</li>
<li>int tevent_loop_once()</li>
</ul>

Both of functions accept just one parameter (tevent context) and the only
difference lies in the fact that the first loop can theoretically last for ever
but the second one will wait just for a single one event to catch and then the
loop breaks and the program continue.

*/