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design: bufferpool: fix markup on sample code block

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Reynaldo H. Verdejo Pinochet 2017-01-24 14:31:52 -08:00
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markdown/design/bufferpool.md
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@ -1,6 +1,6 @@
# Bufferpool
This document details the design of how buffers are be allocated and
This document details the design of how buffers are allocated and
managed in pools.
Bufferpools increase performance by reducing allocation overhead and
@ -33,8 +33,7 @@ properties:
- Notify upstream element of new bufferpool availability. This is
important when a new element, that can provide a bufferpool, is
dynamically linked
downstream.
dynamically linked downstream.
## GstBufferPool
@ -63,8 +62,8 @@ The srcpad will always take the initiative to negotiate the allocation
properties. It starts with creating a `GST_QUERY_ALLOCATION` with the negotiated
caps.
The srcpad can set the need-pool flag to TRUE in the query to optionally make the
peer pad allocate a bufferpool. It should only do this if it is able to use
The srcpad can set the need-pool flag to TRUE in the query to optionally make
the peer pad allocate a bufferpool. It should only do this if it is able to use
the peer provided bufferpool.
It will then inspect the returned results and configure the returned pool or
@ -73,8 +72,8 @@ create a new pool with the returned properties when needed.
Buffers are then allocated by the srcpad from the negotiated pool and pushed to
the peer pad as usual.
The allocation query can also return an allocator object when the buffers are of
different sizes and can't be allocated from a pool.
The allocation query can also return an allocator object when the buffers are
of different sizes and can't be allocated from a pool.
## Allocation query
@ -86,14 +85,14 @@ The allocation query has the following fields:
* (out) **`pool`**, `G_TYPE_ARRAY` of structure: an array of pool configurations:
`` c
``` c
struct {
GstBufferPool *pool;
guint size;
guint min_buffers;
guint max_buffers;
}
``
```
Use `gst_query_parse_nth_allocation_pool()` to get the values.
@ -113,7 +112,8 @@ acceptable.
The pool can then be configured with the suggested min and max amount of
buffers or a downstream element might choose different values.
* (out) **`allocator`**, `G_TYPE_ARRAY` of structure: an array of allocator parameters that can be used.
* (out) **`allocator`**, `G_TYPE_ARRAY` of structure: an array of allocator
parameters that can be used.
``` c
struct {
@ -129,7 +129,8 @@ parameters to allocate memory for the downstream element.
It is also possible to configure the allocator in a provided pool.
* (out) **`metadata`**, `G_TYPE_ARRAY` of structure: an array of metadata params that can be accepted.
* (out) **`metadata`**, `G_TYPE_ARRAY` of structure: an array of metadata
params that can be accepted.
``` c
struct {
@ -156,8 +157,8 @@ res = gst_buffer_pool_acquire_buffer (pool, &buffer, &params);
```
A `GstBuffer` that is allocated from the pool will always be writable (have a
refcount of 1) and it will also have its pool member point to the `GstBufferPool`
that created the buffer.
refcount of 1) and it will also have its pool member point to the
`GstBufferPool` that created the buffer.
Buffers are refcounted in the usual way. When the refcount of the buffer
reaches 0, the buffer is automatically returned to the pool.
@ -170,22 +171,21 @@ the inactive state we can drain all buffers from the pool.
When the pool is in the inactive state, `gst_buffer_pool_acquire_buffer()` will
return `GST_FLOW_FLUSHING` immediately.
Extra parameters can be given to the `gst_buffer_pool_acquire_buffer()` method to
influence the allocation decision. `GST_BUFFER_POOL_ACQUIRE_FLAG_KEY_UNIT` and
`GST_BUFFER_POOL_ACQUIRE_FLAG_DISCONT` serve as hints.
Extra parameters can be given to the `gst_buffer_pool_acquire_buffer()` method
to influence the allocation decision. `GST_BUFFER_POOL_ACQUIRE_FLAG_KEY_UNIT`
and `GST_BUFFER_POOL_ACQUIRE_FLAG_DISCONT` serve as hints.
When the bufferpool is configured with a maximum number of buffers, allocation
will block when all buffers are outstanding until a buffer is returned to the
pool. This behaviour can be changed by specifying the
`GST_BUFFER_POOL_ACQUIRE_FLAG_DONTWAIT` flag in the parameters. With this flag set,
allocation will return `GST_FLOW_EOS` when the pool is empty.
`GST_BUFFER_POOL_ACQUIRE_FLAG_DONTWAIT` flag in the parameters. With this flag
set, allocation will return `GST_FLOW_EOS` when the pool is empty.
## Renegotiation
Renegotiation of the bufferpool might need to be performed when the
configuration of the pool changes. Changes can be in the buffer size
(because of a caps change), alignment or number of
buffers.
(because of a caps change), alignment or number of buffers.
### Downstream