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docs: update design docs

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Update design docs with some info about how the lifecycle of fds
are managed.
This commit is contained in:
Wim Taymans 2015-12-04 16:39:29 +01:00
parent f82f6ce5e0
commit 9bdc9d757a
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117
doc/design.txt
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@ -50,6 +50,123 @@ generic and extensible and allows for inline serialized events such as
property changes and format changes.
fd management
-------------
Pinos shares data between clients by using fd passing. Sometimes the memory
referenced by the fd needs to be reused. It is important that all pinos
clients lost their reference to the fd before it can be reused.
What follows are some scenarios of how the lifecycle of the fds are
managed.
* server side
v4l2src pinospay multisocketsink
| | |
| | |
make buffer |--------->| |
| | (1) |
| |------------>| (2) ----->
| | |
| |<------------|
| (4)| ............| (3)
| | |
|... | ... |
| | |
| |<------------| (5) <-----
| (6)| |
| | |
(1) pinospay generates the pinos message for the v4l2 input
buffer. It is assumed in the next steps that the payloader
receives fd-memory from v4l2src and that the memory is only
freed again when no clients are looking at the fd.
(2) multisocketsink sends the buffer to N Pinos clients
(3) for each client that is sent a buffer, multisocketsink sends an
event with the client object and buffer in it.
(4) pinospay maps the fd-index that was sent, to the buffer in a
hashtable for each client. It refs the buffer so that it remains
alive for as long as the client is using the buffer.
(5) when a message is received from a client, multisocketsink sends an
event upstream.
(6) pinospay parses the message and removes all fd-index entries from
the client hashtable. When all clients release the fd, the buffer
will be unreffed and v4l2src can reuse the memory.
* client consumer
pinossrc xvimagesink
| |
-------> (1)|------------------->| (2)
| |
| (3) |
|<-------------------|
<------- (4)| |
| |
(1) pinossrc receives a buffer from Pinos and wraps the fd with data
in an fd-memory. It remembers the fd-index as qdata on the memory.
It has a special DestroyNotify on the qdata.
(2) xvimagesink renders the buffer and frees the buffer.
(3) freeing the buffer causes the qdata DestoyNotify to be called.
(4) pinossrc constructs a release-fd message and sends it to Pinos
* client producer
videotestsrc pinossink
| |
(1)|------------------->|
| | (2) ----->
| |
| (4) | (3) <-----
|<-------------------|
(1) videotestsrc produces a buffer
(2) pinossink makes a PinosBuffer from the input buffer. It will also
keep the buffer in a hash table indexed by the fd-index.
(3) pinossink receives an fd-release message from Pinos. It removes
the fd-index from the hashtable and
the hashtable and the buffer is unreffed
(4) the fd is returned to videotestsrc for reuse.
* client producer, server side
socketsrc pinospay multisocketsink
| | |
------> (1) | (2)| |
|----------->| |
| |------------>| (3) -------->
| | | ....
| (5)|<------------| (4)
| | ...... |
| | |
| (7)|<------------| (6) <--------
<------- (8)|<-----------| |
| | |
(1) pinos buffer arrives from a client. socketsrc wraps the
fd
(2) pinospay sets a weak-ref on the buffer to know when it is
freed.
(3) multisocketsink sends the buffer to the clients
(4) for each buffer that is sent, an event is sent to the payloader
(5) the payloader remembers the fd-index and buffer in a per-client
hashtable. it keeps a ref on the buffer
(6) release-fd is received from a client
(7) pinospay removes the fd-index from the client hashtable. If all
clients released the fd, the buffer will be freeds, triggering
the DestroyNotify. This will then trigger an event with a release-fd
message to the source.
(8) the source sends the release-fd message to Pinos
Wire
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