gstreamer/docs/random/wtay/scheduling_ideas

Element types
-------------

SOURCES
-------

* never chain-based
* have no sinkpads

1) get based src

   (----------)
   ! fakesrc  !
   !         src-   (get based)
   (----------)

  * no sinkpads
  * srcpad(s) that are get-based

2) loop based src

   (----------)
   ! fakesrc  !
   !         src-   (loop based)
   (----------)

  * no sinkpads
  * element is loop-based
  * data is pushed on the srcpad(s)

FILTERS
-------

3) chain based filter

   (----------)
   ! identity !
 -sink       src- 
   (----------)

  * sinkpad(s) have a chain function
  * srcpad(s) push data

4) loop-based filter

   (----------)
   ! identity !
 -sink       src- 
   (----------)

  * element is loop-based
  * data is pushed on the srcpads
  * data is pulled from sinkpad(s)


SINKS
-----

5) chain based sink

   (----------)
   ! fakesink !
 -sink        !
   (----------)

  * sinkpad(s) have a chain function
  * no srcpads

6) loop-based sink

   (----------)
   ! fakesink !
 -sink        !
   (----------)

  * element is loop-based
  * data is pulled from sinkpad(s)


DECOUPLED
---------

7) decoupled element


   (----------)
   ! queue    !
 -sink       src- 
   (----------)

  * sinkpad(s) have chain function
  * srcpad(s) have get function
  * never loop-based
  * always acts like a chain-based sink for upstream elements
  * always acts like a get-based src for downstream elements
  * are not added to a group, but marked as an entry point in 
    case it acts as a src element


Connection types
----------------

1) get based src
2) loop based src
3) chain based filter
4) loop-based filter
5) chain based sink
6) loop-based sink
7) decoupled element


   !  1  !  2  !  3  !  4  !  5  !  6  !  7  !
---+-----+-----+-----+-----+-----+-----+-----+
 1 !  X  !  X  !  A  !  C  !  A  !  C  !  A  !
   !     !     !     !     !     !     !     !
 2 !  X  !  X  !  B  !  F  !  B  !  F  !  B  !
   !     !     !     !     !     !     !     !
 3 !  X  !  X  !  D  !  E  !  D  !  E  !  D  !
   !     !     !     !     !     !     !     !
 4 !  X  !  X  !  B  !  F  !  B  !  F  !  B  !
   !     !     !     !     !     !     !     !
 5 !  X  !  X  !  X  !  X  !  X  !  X  !  X  !
   !     !     !     !     !     !     !     !
 6 !  X  !  X  !  X  !  X  !  X  !  X  !  X  !
   !     !     !     !     !     !     !     !
 7 !  X  !  X  !  A  !  C  !  A  !  C  !  X  !
   !     !     !     !     !     !     !     !


A)

  src       -> sink
  src       -> filter
  src       -> decoupled
  decoupled -> sink
  decoupled -> filter

 - get based source
 - chain based sink

  * one group
  * src at start of group and entry point
  * _get from src, push to sink

  (-group1---------------)
  !                      !
  ! *fakesrc -> fakesink !
  (----------------------)


B)

  src    -> sink
  src    -> filter
  src    -> decoupled
  filter -> sink
  filter -> filter
  filter -> decoupled

 - loop based source/filter
 - chain based sink/filter/decoupled

 * one group
 * src/filter at start of group and entry point
 * loop on src, chainhandler set to chain function

  (-group1----------------)
  !                       !
  ! %*fakesrc -> fakesink !
  (-----------------------)


C) 

  src       -> sink
  src       -> filter
  decoupled -> sink
  decoupled -> filter

 - get based source/decoupled
 - loop based sink/filter

 * one group
 * loop based element is entry point
 * loop on sink/filter, gethandler set to getfunction
 
  (-group1----------------)
  !                       !
  ! fakesrc -> %*fakesink !
  (-----------------------)

D)

  filter -> filter
  filter -> sink
  filter -> decoupled

  - chain based filter
  - chain based filter/sink/decoupled

  * one group is created to hold the two elements
  * no entry point
  * chainhandler set to peer chainfunction
  
  (-group1----------------)
  !                       !
  ! identity -> identity  !
  (-----------------------)

E)

  filter  -> filter
  filter  -> sink

  - chain based filter
  - loop based filter/sink

  * two groups
  * group is created for src element if needed
  * chainhandler of loop based element set to loop wrapper, control is
    handed to the peer group
  * gethandler of loop based element set to get wrapper

  (-group1---)  (-group2------)
  !          !  !             !
  ! identity ---> %*identity  !
  (----------)  (-------------)


F)

  src     -> filter
  src     -> sink
  filter  -> filter
  filter  -> sink

  - loop based filter/src
  - loop based filter/sink

  * two groups
  * two entry points
  * chainhandler set to loop wrapper
  * gethandler set to get wrapper
  
  (-group1-----)  (-group2------)
  !            !  !             !
  ! %*identity ---> %*identity  !
  (------------)  (-------------)


Grouping
--------

 * a group has at most one loop based element
 * elements in a group are sorted, src elements first (not mandatory)
 * a group has one cothread
 * a group is created immediatly for loop based elements, all other elements
   are added to a group when a pad connection is made
 * get-based plugins are put in the same group as a peer loop based element
 * chain based elements are put in the same group as sink peer elements
 * entry point in the group is:
   - loopbased element 
   - first src element if no loopbased element exists in the group

Result: you end up with a group of connected elements with either:
    - a loop based plugin as the entry point
    - a get based plugin as the entry point

Scheduling the group is a matter of starting the cothread and calling
the loop function or doing a _get/_push on a srcpad.


other examples of groups:
-------------------------

 % = loop based
 * = entry point of group
   
.
  (-group1---------------)
  !                      !
  ! *fakesrc -> fakesink !
  (----------------------)

.
  (-group1---------------------------------------)
  !                                              !
  ! *fakesrc -> identity -> identity -> fakesink !
  (----------------------------------------------)

.
  (-group1-----------------------------------------)
  !                                                !
  ! fakesrc -> %*identity -> identity -> fakesink  !
  (------------------------------------------------)

.
  (-group1---------------) (-group2-----------------)
  !                      ! !                        !
  ! *fakesrc -> identity --> *%identity -> fakesink !
  (----------------------) (------------------------)

.
  (-group1------------------------------------)
  !                                           ! 
  ! *fakesrc -> tee  --> identity -> fakesink !
  !                  --> identity -> fakesink !  
  (-------------------------------------------)

.
  (-group1------------------------------------)
  !                                           ! 
  ! *fakesrc -> tee  --> identity -> fakesink !
  (--------------!----------------------------)
                 v
              (-group2-----------------)
              !                        !
              ! *%identity -> fakesink !
              (------------------------)

.
  (-group1----------) (-group2-----------------)
  !                 ! !                        !
  ! *fakesrc -> tee --> *%identity -> fakesink !
  (--------------!--) (------------------------)
                 v
              (-group3-----------------)
              !                        !
              ! *%identity -> fakesink !
              (------------------------)

.
  (-group1-----------------------) (-group2----------------------)
  !                              ! !                             !
  ! filesrc -> *%mpegdemux  --> queue* -> mpeg2dec -> xvideosink !
  !                              ! (-----------------------------)
  !                              ! (-group3----------------------)
  !                              ! !                             !
  !                         --> queue* -> mad -> osssink         !  
  (------------------------------) (-----------------------------)


Chaining
--------

 * groups that are connected end up in the same chain
 * a group always belongs to a chain
 * updating the chain is only needed when two groups are
   connected with a connection of type E/F. for other
   connection types, the group itself is updated.
 * a chain is scheduled by scheduling a random group in the chain.


Wrapper functions
-----------------