1tevent_context(3)                   tevent                   tevent_context(3)
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NAME

6       tevent_context - Chapter 1: Tevent context
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Tevent context

10       Tevent context is an essential logical unit of tevent library. For
11       working with events at least one such context has to be created -
12       allocated, initialized. Then, events which are meant to be caught and
13       handled have to be registered within this specific context. Reason for
14       subordinating events to a tevent context structure rises from the fact
15       that several context can be created and each of them is processed at
16       different time. So, there can be 1 context containing just file
17       descriptor events, another one taking care of signal and time events
18       and the third one which keeps information about the rest.
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20       Tevent loops are the part of the library which represents the mechanism
21       where noticing events and triggering handlers actually happens. They
22       accept just one argument - tevent context structure. Therefore if
23       theoretically an infinity loop (tevent_loop_wait) was called, only
24       those arguments which belong to the passed tevent context structure can
25       be caught and invoked within this call. Although some more signal
26       events were registered (but within some other context) they will not be
27       noticed.
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29   Example
30       First lines which handle mem_ctx belong to talloc library knowledge but
31       because of the fact that tevent uses the talloc library for its
32       mechanisms it is necessary to understand a bit talloc as well. For more
33       information about working with talloc, please visit talloc website
34       where tutorial and documentation are located.
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36       Tevent context structure *event_ctx represents the unit which will
37       further contain information about registered events. It is created via
38       calling tevent_context_init().
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40       TALLOC_CTX *mem_ctx = talloc_new(NULL);
41       if (mem_ctx == NULL) {
42           // error handling
43       }
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45       struct tevent_context *ev_ctx = tevent_context_init(mem_ctx);
46       if(ev_ctx == NULL) {
47           // error handling
48       }
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50       Tevent context has a structure containing lots of information. It
51       include lists of all events which are divided according their type and
52       are in order showing the sequence as they came.
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54       In addition to the lists shown in the diagram, the tevent context also
55       contains many other data (e.g. information about the available system
56       mechanism for triggering callbacks).
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Tevent loops

59       Tevent loops are the dispatcher for events. They catch them and trigger
60       the handlers. In the case of longer processes, the program spends most
61       of its time at this point waiting for events, invoking handlers and
62       waiting for another event again. There are 2 types of loop available
63       for use in tevent library:
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65       · int tevent_loop_wait()
66       · int tevent_loop_once()
67       Both of functions accept just one parameter (tevent context) and the
68       only difference lies in the fact that the first loop can theoretically
69       last for ever but the second one will wait just for a single one event
70       to catch and then the loop breaks and the program continue.
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74Version 0.9.8                   Fri Jul 13 2018              tevent_context(3)
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