Many programs will want to manage sound resources for things such as reference counting and streaming. This is supported by miniaudio via the
`ma_resource_manager` API.
Many programs will want to manage sound resources for things such as reference counting and
streaming. This is supported by miniaudio via the `ma_resource_manager` API.
The resource manager is mainly responsible for the following:
1) Loading of sound files into memory with reference counting.
2) Streaming of sound data
When loading a sound file, the resource manager will give you back a data source compatible object called `ma_resource_manager_data_source`. This object can be
passed into any `ma_data_source` API which is how you can read and seek audio data. When loading a sound file, you specify whether or not you want the sound to
be fully loaded into memory (and optionally pre-decoded) or streamed. When loading into memory, you can also specify whether or not you want the data to be
loaded asynchronously.
When loading a sound file, the resource manager will give you back a `ma_data_source` compatible
object called `ma_resource_manager_data_source`. This object can be passed into any
`ma_data_source` API which is how you can read and seek audio data. When loading a sound file, you
specify whether or not you want the sound to be fully loaded into memory (and optionally
pre-decoded) or streamed. When loading into memory, you can also specify whether or not you want
the data to be loaded asynchronously.
The example below is how you can initialize a resource manager using it's default configuration:
...
...
@@ -66,9 +68,11 @@ The example below is how you can initialize a resource manager using it's defaul
}
```
You can configure the format, channels and sample rate of the decoded audio data. By default it will use the file's native data format, but you can configure
it to use a consistent format. This is useful for offloading the cost of data conversion to load time rather than dynamically converting a mixing time. To do
this, you configure the decoded format, channels and sample rate like the code below:
You can configure the format, channels and sample rate of the decoded audio data. By default it
will use the file's native data format, but you can configure it to use a consistent format. This
is useful for offloading the cost of data conversion to load time rather than dynamically
converting a mixing time. To do this, you configure the decoded format, channels and sample rate
like the code below:
```c
config = ma_resource_manager_config_init();
...
...
@@ -77,21 +81,26 @@ this, you configure the decoded format, channels and sample rate like the code b
config.decodedSampleRate = device.sampleRate;
```
In the code above, the resource manager will be configured so that any decoded audio data will be pre-converted at load time to the device's native data
format. If instead you used defaults and the data format of the file did not match the device's data format, you would need to convert the data at mixing time
which may be prohibitive in high-performance and large scale scenarios like games.
In the code above, the resource manager will be configured so that any decoded audio data will be
pre-converted at load time to the device's native data format. If instead you used defaults and
the data format of the file did not match the device's data format, you would need to convert the
data at mixing time which may be prohibitive in high-performance and large scale scenarios like
games.
Asynchronicity is achieved via a job system. When an operation needs to be performed, such as the decoding of a page, a job will be posted to a queue which
will then be processed by a job thread. By default there will be only one job thread running, but this can be configured, like so:
Asynchronicity is achieved via a job system. When an operation needs to be performed, such as the
decoding of a page, a job will be posted to a queue which will then be processed by a job thread.
By default there will be only one job thread running, but this can be configured, like so:
```c
config = ma_resource_manager_config_init();
config.jobThreadCount = MY_JOB_THREAD_COUNT;
```
By default job threads are managed internally by the resource manager, however you can also self-manage your job threads if, for example, you want to integrate
the job processing into your existing job infrastructure, or if you simply don't like the way the resource manager does it. To do this, just set the job thread
count to 0 and process jobs manually. To process jobs, you first need to retrieve a job using `ma_resource_manager_next_job()` and then process it using
By default job threads are managed internally by the resource manager, however you can also self
manage your job threads if, for example, you want to integrate the job processing into your
existing job infrastructure, or if you simply don't like the way the resource manager does it. To
do this, just set the job thread count to 0 and process jobs manually. To process jobs, you first
need to retrieve a job using `ma_resource_manager_next_job()` and then process it using
`ma_resource_manager_process_job()`:
```c
...
...
@@ -125,12 +134,13 @@ count to 0 and process jobs manually. To process jobs, you first need to retriev
}
```
In the example above, the MA_JOB_QUIT event is the used as the termination indicator. You can instead use whatever variable you would like to terminate the
thread. The call to `ma_resource_manager_next_job()` is blocking by default, by can be configured to be non-blocking by initializing the resource manager
with the MA_RESOURCE_MANAGER_FLAG_NON_BLOCKING configuration flag.
In the example above, the `MA_JOB_QUIT` event is the used as the termination indicator, but you can
use whatever you would like to terminate the thread. The call to `ma_resource_manager_next_job()`
is blocking by default, by can be configured to be non-blocking by initializing the resource
manager with the `MA_RESOURCE_MANAGER_FLAG_NON_BLOCKING` configuration flag.
When loading a file, it's sometimes convenient to be able to customize how files are opened and read. This can be done by setting `pVFS` member of the
resource manager's config:
When loading a file, it's sometimes convenient to be able to customize how files are opened and
read. This can be done by setting `pVFS` member of the resource manager's config:
```c
// Initialize your custom VFS object. See documentation for VFS for information on how to do this.
...
...
@@ -140,11 +150,14 @@ resource manager's config:
config.pVFS = &vfs;
```
If you do not specify a custom VFS, the resource manager will use the operating system's normal file operations. This is default.
If you do not specify a custom VFS, the resource manager will use the operating system's normal
file operations. This is default.
To load a sound file and create a data source, call `ma_resource_manager_data_source_init()`. When loading a sound you need to specify the file path and
options for how the sounds should be loaded. By default a sound will be loaded synchronously. The returned data source is owned by the caller which means the
caller is responsible for the allocation and freeing of the data source. Below is an example for initializing a data source:
To load a sound file and create a data source, call `ma_resource_manager_data_source_init()`. When
loading a sound you need to specify the file path and options for how the sounds should be loaded.
By default a sound will be loaded synchronously. The returned data source is owned by the caller
which means the caller is responsible for the allocation and freeing of the data source. Below is
an example for initializing a data source:
```c
ma_resource_manager_data_source dataSource;
...
...
@@ -167,7 +180,8 @@ caller is responsible for the allocation and freeing of the data source. Below i
The `flags` parameter specifies how you want to perform loading of the sound file. It can be a combination of the following flags:
The `flags` parameter specifies how you want to perform loading of the sound file. It can be a
combination of the following flags:
```
MA_DATA_SOURCE_STREAM
...
...
@@ -175,134 +189,187 @@ The `flags` parameter specifies how you want to perform loading of the sound fil
MA_DATA_SOURCE_ASYNC
```
When no flags are specified (set to 0), the sound will be fully loaded into memory, but not decoded, meaning the raw file data will be stored in memory, and
then dynamically decoded when `ma_data_source_read_pcm_frames()` is called. To instead decode the audio data before storing it in memory, use the
`MA_DATA_SOURCE_DECODE` flag. By default, the sound file will be loaded synchronously, meaning `ma_resource_manager_data_source_init()` will only return after
the entire file has been loaded. This is good for simplicity, but can be prohibitively slow. You can instead load the sound asynchronously using the
`MA_DATA_SOURCE_ASYNC` flag. This will result in `ma_resource_manager_data_source_init()` returning quickly, but no data will be returned by
`ma_data_source_read_pcm_frames()` until some data is available. When no data is available because the asynchronous decoding hasn't caught up, MA_BUSY will be
returned by `ma_data_source_read_pcm_frames()`.
For large sounds, it's often prohibitive to store the entire file in memory. To mitigate this, you can instead stream audio data which you can do by specifying
the `MA_DATA_SOURCE_STREAM` flag. When streaming, data will be decoded in 1 second pages. When a new page needs to be decoded, a job will be posted to the job
queue and then subsequently processed in a job thread.
When loading asynchronously, it can be useful to poll whether or not loading has finished. Use `ma_resource_manager_data_source_result()` to determine this.
For in-memory sounds, this will return `MA_SUCCESS` when the file has been *entirely* decoded. If the sound is still being decoded, `MA_BUSY` will be returned.
Otherwise, some other error code will be returned if the sound failed to load. For streaming data sources, `MA_SUCCESS` will be returned when the first page
has been decoded and the sound is ready to be played. If the first page is still being decoded, `MA_BUSY` will be returned. Otherwise, some other error code
will be returned if the sound failed to load.
For in-memory sounds, reference counting is used to ensure the data is loaded only once. This means multiple calls to `ma_resource_manager_data_source_init()`
with the same file path will result in the file data only being loaded once. Each call to `ma_resource_manager_data_source_init()` must be matched up with a
call to `ma_resource_manager_data_source_uninit()`. Sometimes it can be useful for a program to register self-managed raw audio data and associate it with a
file path. Use `ma_resource_manager_register_decoded_data()`, `ma_resource_manager_register_encoded_data()` and `ma_resource_manager_unregister_data()` to do
this. `ma_resource_manager_register_decoded_data()` is used to associate a pointer to raw, self-managed decoded audio data in the specified data format with
the specified name. Likewise, `ma_resource_manager_register_encoded_data()` is used to associate a pointer to raw self-managed encoded audio data (the raw
file data) with the specified name. Note that these names need not be actual file paths. When `ma_resource_manager_data_source_init()` is called (without the
`MA_DATA_SOURCE_STREAM` flag), the resource manager will look for these explicitly registered data buffers and, if found, will use it as the backing data for
the data source. Note that the resource manager does *not* make a copy of this data so it is up to the caller to ensure the pointer stays valid for it's
lifetime. Use `ma_resource_manager_unregister_data()` to unregister the self-managed data. It does not make sense to use the `MA_DATA_SOURCE_STREAM` flag with
a self-managed data pointer. When `MA_DATA_SOURCE_STREAM` is specified, it will try loading the file data through the VFS.
When no flags are specified (set to 0), the sound will be fully loaded into memory, but not
decoded, meaning the raw file data will be stored in memory, and then dynamically decoded when
`ma_data_source_read_pcm_frames()` is called. To instead decode the audio data before storing it in
memory, use the `MA_DATA_SOURCE_DECODE` flag. By default, the sound file will be loaded
synchronously, meaning `ma_resource_manager_data_source_init()` will only return after the entire
file has been loaded. This is good for simplicity, but can be prohibitively slow. You can instead
load the sound asynchronously using the `MA_DATA_SOURCE_ASYNC` flag. This will result in
`ma_resource_manager_data_source_init()` returning quickly, but no data will be returned by
`ma_data_source_read_pcm_frames()` until some data is available. When no data is available because
the asynchronous decoding hasn't caught up, `MA_BUSY` will be returned by
`ma_data_source_read_pcm_frames()`.
For large sounds, it's often prohibitive to store the entire file in memory. To mitigate this, you
can instead stream audio data which you can do by specifying the `MA_DATA_SOURCE_STREAM` flag. When
streaming, data will be decoded in 1 second pages. When a new page needs to be decoded, a job will
be posted to the job queue and then subsequently processed in a job thread.
When loading asynchronously, it can be useful to poll whether or not loading has finished. Use
`ma_resource_manager_data_source_result()` to determine this. For in-memory sounds, this will
return `MA_SUCCESS` when the file has been *entirely* decoded. If the sound is still being decoded,
`MA_BUSY` will be returned. Otherwise, some other error code will be returned if the sound failed
to load. For streaming data sources, `MA_SUCCESS` will be returned when the first page has been
decoded and the sound is ready to be played. If the first page is still being decoded, `MA_BUSY`
will be returned. Otherwise, some other error code will be returned if the sound failed to load.
For in-memory sounds, reference counting is used to ensure the data is loaded only once. This means
multiple calls to `ma_resource_manager_data_source_init()` with the same file path will result in
the file data only being loaded once. Each call to `ma_resource_manager_data_source_init()` must be
matched up with a call to `ma_resource_manager_data_source_uninit()`. Sometimes it can be useful
for a program to register self-managed raw audio data and associate it with a file path. Use the
`ma_resource_manager_register_*()` and `ma_resource_manager_unregister_*()` APIs to do this.
`ma_resource_manager_register_decoded_data()` is used to associate a pointer to raw, self-managed
decoded audio data in the specified data format with the specified name. Likewise,
`ma_resource_manager_register_encoded_data()` is used to associate a pointer to raw self-managed
encoded audio data (the raw file data) with the specified name. Note that these names need not be
actual file paths. When `ma_resource_manager_data_source_init()` is called (without the
`MA_DATA_SOURCE_STREAM` flag), the resource manager will look for these explicitly registered data
buffers and, if found, will use it as the backing data for the data source. Note that the resource
manager does *not* make a copy of this data so it is up to the caller to ensure the pointer stays
valid for it's lifetime. Use `ma_resource_manager_unregister_data()` to unregister the self-managed
data. It does not make sense to use the `MA_DATA_SOURCE_STREAM` flag with a self-managed data
pointer. When `MA_DATA_SOURCE_STREAM` is specified, it will try loading the file data through the
VFS.
Resource Manager Implementation Details
---------------------------------------
Resources are managed in two main ways:
1) By storing the entire sound inside an in-memory buffer (referred to as a data buffer - `ma_resource_manager_data_buffer_node`)
2) By streaming audio data on the fly (referred to as a data stream - `ma_resource_manager_data_stream`)
A resource managed data source (`ma_resource_manager_data_source`) encapsulates a data buffer or data stream, depending on whether or not the data source was
initialized with the `MA_DATA_SOURCE_FLAG_STREAM` flag. If so, it will make use of a `ma_resource_manager_data_stream` object. Otherwise it will use a
`ma_resource_manager_data_buffer_node` object.
Another major feature of the resource manager is the ability to asynchronously decode audio files. This relieves the audio thread of time-consuming decoding
which can negatively affect scalability due to the audio thread needing to complete it's work extremely quickly to avoid glitching. Asynchronous decoding is
achieved through a job system. There is a central multi-producer, multi-consumer, lock-free, fixed-capacity job queue. When some asynchronous work needs to be
done, a job is posted to the queue which is then read by a job thread. The number of job threads can be configured for improved scalability, and job threads
can all run in parallel without needing to worry about the order of execution (how this is achieved is explained below).
When a sound is being loaded asynchronously, playback can begin before the sound has been fully decoded. This enables the application to start playback of the
sound quickly, while at the same time allowing to resource manager to keep loading in the background. Since there may be less threads than the number of sounds
being loaded at a given time, a simple scheduling system is used to keep decoding time fair. The resource manager solves this by splitting decoding into chunks
called pages. By default, each page is 1 second long. When a page has been decoded, the a new job will be posted to start decoding the next page. By dividing
up decoding into pages, an individual sound shouldn't ever delay every other sound from having their first page decoded. Of course, when loading many sounds at
the same time, there will always be an amount of time required to process jobs in the queue so in heavy load situations there will still be some delay. To
determine if a data source is ready to have some frames read, use `ma_resource_manager_data_source_get_available_frames()`. This will return the number of
frames available starting from the current position.
1) By storing the entire sound inside an in-memory buffer (referred to as a data buffer)
2) By streaming audio data on the fly (referred to as a data stream)
A resource managed data source (`ma_resource_manager_data_source`) encapsulates a data buffer or
data stream, depending on whether or not the data source was initialized with the
`MA_DATA_SOURCE_FLAG_STREAM` flag. If so, it will make use of a `ma_resource_manager_data_stream`
object. Otherwise it will use a `ma_resource_manager_data_buffer` object. Both of these objects
are data sources which means they can be used with any `ma_data_source_*()` API.
Another major feature of the resource manager is the ability to asynchronously decode audio files.
This relieves the audio thread of time-consuming decoding which can negatively affect scalability
due to the audio thread needing to complete it's work extremely quickly to avoid glitching.
Asynchronous decoding is achieved through a job system. There is a central multi-producer,
multi-consumer, lock-free, fixed-capacity job queue. When some asynchronous work needs to be done,
a job is posted to the queue which is then read by a job thread. The number of job threads can be
configured for improved scalability, and job threads can all run in parallel without needing to
worry about the order of execution (how this is achieved is explained below).
When a sound is being loaded asynchronously, playback can begin before the sound has been fully
decoded. This enables the application to start playback of the sound quickly, while at the same
time allowing to resource manager to keep loading in the background. Since there may be less
threads than the number of sounds being loaded at a given time, a simple scheduling system is used
to keep decoding time balanced and fair. The resource manager solves this by splitting decoding
into chunks called pages. By default, each page is 1 second long. When a page has been decoded, a
new job will be posted to start decoding the next page. By dividing up decoding into pages, an
individual sound shouldn't ever delay every other sound from having their first page decoded. Of
course, when loading many sounds at the same time, there will always be an amount of time required
to process jobs in the queue so in heavy load situations there will still be some delay. To
determine if a data source is ready to have some frames read, use
`ma_resource_manager_data_source_get_available_frames()`. This will return the number of frames
available starting from the current position.
Data Buffers
------------
When the `MA_DATA_SOURCE_FLAG_STREAM` flag is not specified at initialization time, the resource manager will try to load the data into an in-memory data
buffer. Before doing so, however, it will first check if the specified file has already been loaded. If so, it will increment a reference counter and just use
the already loaded data. This saves both time and memory. A binary search tree (BST) is used for storing data buffers as it has good balance between efficiency
and simplicity. The key of the BST is a 64-bit hash of the file path that was passed into `ma_resource_manager_data_source_init()`. The advantage of using a
hash is that it saves memory over storing the entire path, has faster comparisons, and results in a mostly balanced BST due to the random nature of the hash.
The disadvantage is that file names are case-sensitive. If this is an issue, you should normalize your file names to upper- or lower-case before initializing
your data sources.
When a sound file has not already been loaded and the `MA_DATA_SOURCE_ASYNC` is not specified, the file will be decoded synchronously by the calling thread.
There are two options for controlling how the audio is stored in the data buffer - encoded or decoded. When the `MA_DATA_SOURCE_DECODE` option is not
specified, the raw file data will be stored in memory. Otherwise the sound will be decoded before storing it in memory. Synchronous loading is a very simple
and standard process of simply adding an item to the BST, allocating a block of memory and then decoding (if `MA_DATA_SOURCE_DECODE` is specified).
When the `MA_DATA_SOURCE_ASYNC` flag is specified, loading of the data buffer is done asynchronously. In this case, a job is posted to the queue to start
loading and then the function instantly returns, setting an internal result code to `MA_BUSY`. This result code is returned when the program calls
`ma_resource_manager_data_source_result()`. When decoding has fully completed, `MA_RESULT` will be returned. This can be used to know if loading has fully
completed.
When loading asynchronously, a single job is posted to the queue of the type `MA_JOB_LOAD_DATA_BUFFER`. This involves making a copy of the file path and
associating it with job. When the job is processed by the job thread, it will first load the file using the VFS associated with the resource manager. When
using a custom VFS, it's important that it be completely thread-safe because it will be used from one or more job threads at the same time. Individual files
should only ever be accessed by one thread at a time, however. After opening the file via the VFS, the job will determine whether or not the file is being
decoded. If not, it simply allocates a block of memory and loads the raw file contents into it and returns. On the other hand, when the file is being decoded,
it will first allocate a decoder on the heap and initialize it. Then it will check if the length of the file is known. If so it will allocate a block of memory
to store the decoded output and initialize it to silence. If the size is unknown, it will allocate room for one page. After memory has been allocated, the
first page will be decoded. If the sound is shorter than a page, the result code will be set to `MA_SUCCESS` and the completion event will be signalled and
loading is now complete. If, however, there is store more to decode, a job with the code `MA_JOB_PAGE_DATA_BUFFER` is posted. This job will decode the next
page and perform the same process if it reaches the end. If there is more to decode, the job will post another `MA_JOB_PAGE_DATA_BUFFER` job which will keep on
happening until the sound has been fully decoded. For sounds of an unknown length, the buffer will be dynamically expanded as necessary, and then shrunk with a
final realloc() when the end of the file has been reached.
When the `MA_DATA_SOURCE_FLAG_STREAM` flag is excluded at initialization time, the resource manager
will try to load the data into an in-memory data buffer. Before doing so, however, it will first
check if the specified file has already been loaded. If so, it will increment a reference counter
and just use the already loaded data. This saves both time and memory. A binary search tree (BST)
is used for storing data buffers as it has good balance between efficiency and simplicity. The key
of the BST is a 64-bit hash of the file path that was passed into
`ma_resource_manager_data_source_init()`. The advantage of using a hash is that it saves memory
over storing the entire path, has faster comparisons, and results in a mostly balanced BST due to
the random nature of the hash. The disadvantage is that file names are case-sensitive. If this is
an issue, you should normalize your file names to upper- or lower-case before initializing your
data sources.
When a sound file has not already been loaded and the `MA_DATA_SOURCE_ASYNC` is excluded, the file
will be decoded synchronously by the calling thread. There are two options for controlling how the
audio is stored in the data buffer - encoded or decoded. When the `MA_DATA_SOURCE_DECODE` option is
excluded, the raw file data will be stored in memory. Otherwise the sound will be decoded before
storing it in memory. Synchronous loading is a very simple and standard process of simply adding an
item to the BST, allocating a block of memory and then decoding (if `MA_DATA_SOURCE_DECODE` is
specified).
When the `MA_DATA_SOURCE_ASYNC` flag is specified, loading of the data buffer is done
asynchronously. In this case, a job is posted to the queue to start loading and then the function
immediately returns, setting an internal result code to `MA_BUSY`. This result code is returned
when the program calls `ma_resource_manager_data_source_result()`. When decoding has fully
completed `MA_RESULT` will be returned. This can be used to know if loading has fully completed.
When loading asynchronously, a single job is posted to the queue of the type
`MA_JOB_LOAD_DATA_BUFFER_NODE`. This involves making a copy of the file path and associating it
with job. When the job is processed by the job thread, it will first load the file using the VFS
associated with the resource manager. When using a custom VFS, it's important that it be completely
thread-safe because it will be used from one or more job threads at the same time. Individual files
should only ever be accessed by one thread at a time, however. After opening the file via the VFS,
the job will determine whether or not the file is being decoded. If not, it simply allocates a
block of memory and loads the raw file contents into it and returns. On the other hand, when the
file is being decoded, it will first allocate a decoder on the heap and initialize it. Then it will
check if the length of the file is known. If so it will allocate a block of memory to store the
decoded output and initialize it to silence. If the size is unknown, it will allocate room for one
page. After memory has been allocated, the first page will be decoded. If the sound is shorter than
a page, the result code will be set to `MA_SUCCESS` and the completion event will be signalled and
loading is now complete. If, however, there is more to decode, a job with the code
`MA_JOB_PAGE_DATA_BUFFER_NODE` is posted. This job will decode the next page and perform the same
process if it reaches the end. If there is more to decode, the job will post another
`MA_JOB_PAGE_DATA_BUFFER_NODE` job which will keep on happening until the sound has been fully
decoded. For sounds of an unknown length, the buffer will be dynamically expanded as necessary,
and then shrunk with a final realloc() when the end of the file has been reached.
Data Streams
------------
Data streams only ever store two pages worth of data for each sound. They are most useful for large sounds like music tracks in games which would consume too
much memory if fully decoded in memory. Only two pages of audio data are stored in memory at a time for each data stream. After every frame from a page has
been read, a job will be posted to load the next page which is done from the VFS.
For data streams, the `MA_DATA_SOURCE_FLAG_ASYNC` flag will determine whether or not initialization of the data source waits until the two pages have been
decoded. When unset, `ma_resource_manager_data_source_init()` will wait until the two pages have been loaded, otherwise it will return immediately.
When frames are read from a data stream using `ma_resource_manager_data_source_read_pcm_frames()`, `MA_BUSY` will be returned if there are no frames available.
If there are some frames available, but less than the number requested, `MA_SUCCESS` will be returned, but the actual number of frames read will be less than
the number requested. Due to the asymchronous nature of data streams, seeking is also asynchronous. If the data stream is in the middle of a seek, `MA_BUSY`
will be returned when trying to read frames.
When `ma_resource_manager_data_source_read_pcm_frames()` results in a page getting fully consumed, a job is posted to load the next page. This will be posted
from the same thread that called `ma_resource_manager_data_source_read_pcm_frames()` which should be lock-free.
Data streams are uninitialized by posting a job to the queue, but the function won't return until that job has been processed. The reason for this is that the
caller owns the data stream object and therefore we need to ensure everything completes before handing back control to the caller. Also, if the data stream is
uninitialized while pages are in the middle of decoding, they must complete before destroying any underlying object and the job system handles this cleanly.
Data streams only ever store two pages worth of data for each instance. They are most useful for
large sounds like music tracks in games that would consume too much memory if fully decoded in
memory. After every frame from a page has been read, a job will be posted to load the next page
which is done from the VFS.
For data streams, the `MA_DATA_SOURCE_FLAG_ASYNC` flag will determine whether or not
initialization of the data source waits until the two pages have been decoded. When unset,
`ma_resource_manager_data_source_init()` will wait until the two pages have been loaded, otherwise
it will return immediately.
When frames are read from a data stream using `ma_resource_manager_data_source_read_pcm_frames()`,
`MA_BUSY` will be returned if there are no frames available. If there are some frames available,
but less than the number requested, `MA_SUCCESS` will be returned, but the actual number of frames
read will be less than the number requested. Due to the asymchronous nature of data streams,
seeking is also asynchronous. If the data stream is in the middle of a seek, `MA_BUSY` will be
returned when trying to read frames.
When `ma_resource_manager_data_source_read_pcm_frames()` results in a page getting fully consumed
a job is posted to load the next page. This will be posted from the same thread that called
`ma_resource_manager_data_source_read_pcm_frames()` which should be lock-free.
Data streams are uninitialized by posting a job to the queue, but the function won't return until
that job has been processed. The reason for this is that the caller owns the data stream object and
therefore miniaudio needs to ensure everything completes before handing back control to the caller.
Also, if the data stream is uninitialized while pages are in the middle of decoding, they must
complete before destroying any underlying object and the job system handles this cleanly.
Job Queue
---------
The resource manager uses a job queue which is multi-producer, multi-consumer, lock-free and fixed-capacity. The lock-free property of the queue is achieved
using the algorithm described by Michael and Scott: Nonblocking Algorithms and Preemption-Safe Locking on Multiprogrammed Shared Memory Multiprocessors. In
order for this to work, only a fixed number of jobs can be allocated and inserted into the queue which is done through a lock-free data structure for
allocating an index into a fixed sized array, with reference counting for mitigation of the ABA problem. The reference count is 32-bit.
For many types of jobs it's important that they execute in a specific order. In these cases, jobs are executed serially. The way in which each type of job
handles this is specific to the job type. For the resource manager, serial execution of jobs is only required on a per-object basis (per data buffer or per
data stream). Each of these objects stores an execution counter. When a job is posted it is associated with an execution counter. When the job is processed, it
checks if the execution counter of the job equals the execution counter of the owning object and if so, processes the job. If the counters are not equal, the
job will be posted back onto the job queue for later processing. When the job finishes processing the execution order of the main object is incremented. This
system means the no matter how many job threads are executing, decoding of an individual sound will always get processed serially. The advantage to having
multiple threads comes into play when loading multiple sounds at the time time.
The resource manager uses a job queue which is multi-producer, multi-consumer, lock-free and
fixed-capacity. The lock-free property of the queue is achieved using the algorithm described by
Michael and Scott: Nonblocking Algorithms and Preemption-Safe Locking on Multiprogrammed Shared
Memory Multiprocessors. In order for this to work, only a fixed number of jobs can be allocated and
inserted into the queue which is done through a lock-free data structure for allocating an index
into a fixed sized array, with reference counting for mitigation of the ABA problem. The reference
count is 32-bit.
For many types of jobs it's important that they execute in a specific order. In these cases, jobs
are executed serially. For the resource manager, serial execution of jobs is only required on a
per-object basis (per data buffer or per data stream). Each of these objects stores an execution
counter. When a job is posted it is associated with an execution counter. When the job is
processed, it checks if the execution counter of the job equals the execution counter of the
owning object and if so, processes the job. If the counters are not equal, the job will be posted
back onto the job queue for later processing. When the job finishes processing the execution order
of the main object is incremented. This system means the no matter how many job threads are
executing, decoding of an individual sound will always get processed serially. The advantage to
having multiple threads comes into play when loading multiple sounds at the time time.
