ltt/branches/poly/doc/developer/requests_servicing_schedulers.txt

   1 Linux Trace Toolkit
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   3 Requests Servicing Schedulers
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   6 Mathieu Desnoyers, 07/06/2004
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   9 In the LTT graphical interface, two main types of events requests may occur :
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  11 - events requests made by a viewer concerning a traceset for a ad hoc
  12   computation.
  13 - events requests made by a viewer concerning a trace for a precomputation.
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  16 Ad Hoc Computation
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  18 The ad hoc computation must be serviced immediately : they are directly
  19 responding to events requests that must be serviced to complete the graphical
  20 widgets'data. This kind of computation may lead to incomplete result as long as
  21 precomputation are not finished. Once precomputation is over, the widgets will
  22 be redrawn if they needed such information. A ad hoc computation is done on a
  23 traceset : the workspace of a tab.
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  25 Precomputation
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  27 Traces are global objects. Only one instance of a trace is opened for all the
  28 program. Precomputation will append data to the traces attributes (states,
  29 statistics). It must inform the widgets which asked for such states or
  30 statistics of their availability. Only one precomputation must be launched for
  31 each trace and no duplication of precomputation must be done.
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  34 Schedulers
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  36 There is one tracesetcontext per traceset. Each reference to a trace by a
  37 traceset also has its own tracecontext. Each trace, by itself, has its own
  38 tracecontext.
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  40 Let's define a scheduler as a g_idle events request servicing function.
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  42 There is one scheduler per traceset context (registered when there are requests
  43 to answer). There is also one scheduler per autonomous trace context (not
  44 related to any traceset context).
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  46 A scheduler processes requests for a specific traceset or trace by combining
  47 time intervals of the requests. It is interruptible by any GTK event. A
  48 precomputation scheduler has a lower priority than a ad hoc computation
  49 scheduler. That means that no precomputation will be performed until there is
  50 no more ad hoc compuation pending. When a scheduler is interrupted, it makes no
  51 assumption about the presence or absence of the current requests in its pool
  52 when it starts back.
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  55 Foreground Scheduler
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  57 There can be one foreground scheduler per traceset (one traceset per tab). It
  58 simply calls the hooks given by the events requests of the viewers for the
  59 specified time intervals.
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  62 Background Scheduler
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  64 It has its own events requests pool. It services them just like a foreground
  65 scheduler. The difference comes in that there may be duplicated requests :
  66 for instance, statistics computation for a trace can be asked by two viewers
  67 at the same time. Another difference is that the hook_data of theses requests
  68 will typically be NULL, and the typical hook function will be located in a
  69 library upon which the viewer depends.
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  71 A viewer is informed of the completeness of its request by its after_request
  72 hook registered along with the events request.
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  75 Hooks Lists
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  77 In order to answer the problems of background processing, we need to add a
  78 reference counter for each hook of a hook list. If the same hook is added twice,
  79 it will be called only once, but it will need two "remove" to be really removed
  80 from the list. Two hooks are identical if they have the same function pointer
  81 and hook_data.
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  84 EventsRequest Structure
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  86 This structure is the element of the events requests pools. The viewer field is
  87 used as an ownership identifier as well as pointer to the data structure upon
  88 which the action applies. Typically, this is a pointer to the viewer's data
  89 structure.
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  91 In a ad hoc events request, a pointer to this structure is used as hook_data in
  92 the hook lists
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  94 The typical case for a background computation is that the hook_data will be set
  95 to NULL instead. No particular hook_data is needed as this type of request does
  96 only modify trace related data structures which are available through the
  97 call_data.
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