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Interface of pa_core

From pulsecore/core.h: "The core structure of PulseAudio. Every PulseAudio daemon contains exactly one of these. It is used for storing kind of global variables for the daemon."

pa_core doesn't have any interesting functions associated with it, it is just a central collection of all the components and globally relevant variables. You're not supposed to modify the fields, at least not directly.

Actually, in addition to being a variable collection, there are two interesting enumerations too.

The most important field is perhaps mainloop. That can be used for communicating with the daemon mainloop, see Daemon Mainloop.

struct pa_core

parent
  • pa_core is a subclass of pa_msgobject, which implies that the first field of pa_core is of type pa_msgobject. It means also that pa_core can receive messages, see "The unnamed enumeration" later on this page. At some point in the future I may write a page about the ?object system used inside PulseAudio. I think documenting the ?pa msgobject API would be useful too.
cookie
  • A random value which may be used to identify this instance of PulseAudio. Not cryptographically secure in any way.
mainloop
  • Pointer to the mainloop API.
clients
  • Currently connected clients. If you're not familiar with the pa_idxset type, see the header.
sinks, sources
  • Currently existing sinks and sources.
sink_inputs, source_outputs
  • Currently existing sink inputs and source outputs.
modules
  • Loaded modules.
scache
  • The sample cache. The contained items are of type pa_scache_entry.
namereg
  • All sink, source and sample names are stored in this hashmap. The hashmap ensures the uniqueness of the names. This is accessed through the namereg interface.
shared
  • Modules can share variables through this "shared hashmap". Instead of using the hashmap functions directly, this variable should be accessed through a separate interface.
default_source_name, default_sink_name
  • Pretty self-explanatory, but do not access these directly, but through pa_namereg_set_default, pa_namereg_get_default_sink_name and pa_namereg_get_default_source_name that are defined in pulsecore/namereg.h.
default_sample_spec
  • When in need of a default format for an audio stream, you'll find it here.
default_n_fragments, default_fragment_size_msec
  • The default buffering settings that should be used by sinks and sources when opening a hardware device.
module_auto_unload_event
  • The module system uses this to poll for modules that should be unloaded. Not for you.
module_defer_unload_event
  • The module system uses this to make mainloop unload modules. Not for you.
subscription_defer_event
  • The subscription system uses this to make mainloop inform the subscribers about an event. Not for you. (What subscription system? See ?Catching Events.)
subscriptions
  • Head of the list of existing subscriptions. Not for you.
subscription_event_queue
  • Head of the list of unprocessed events. Not for you.
subsrciption_event_last
  • Last item of the list of unprocessed events. Not for you.
mempool
  • The memory pool. You may need this as an argument to some functions.
exit_idle_time
  • The time in seconds between the moment the last client has left and the moment pulseaudio exits, if automatic exiting is used.
module_idle_time
  • The time in seconds between the moment the last client has stopped using a module and the moment the module gets unloaded, if the module is set to be automatically unloaded.
scache_idle_time
  • The time in seconds between the moment a sample has been fired last time and the moment the that the sample gets unloaded, if the sample is loaded as "lazy".
quit_event
  • If the daemon is told to exit after a period of idleness, it uses this to track the idle time. Not for you.
scache_auto_unload_event
  • The sample cache uses this to track the time that the lazy samples have been unused. Not for you.
disallow_module_loading
  • Controls whether modules can be loaded (and unloaded) or not.
running_as_daemon
  • If pulseaudio is daemonized, this is one, otherwise zero.
resample_method
  • The resample method that the user has chosen.
is_system_instance
  • This indicates whether pulseaudio is running as a per-user or a system-wide daemon.
high_priority
  • One, if pulseaudio has made itself a high-priority process (i.e. is running with the SCHED_FIFO scheduling class), zero otherwise.
hooks
  • The hooks that can be used to catch events in core, see ?Catching Events.

enum pa_core_hook

The enumeration contains all the events that can be catched synchronously, see ?Catching Events.

The unnamed enumeration

There's this enumeration, that has only two elements: PA_CORE_MESSAGE_UNLOAD_MODULE and PA_CORE_MESSAGE_MAX. It contains all the messages that can be sent from outside the daemon mainloop thread to the core, and currently there is only one such message.

PA_CORE_MESSAGE_UNLOAD_MODULE causes a module (give the pointer as userdata to pa_asyncmsgq_post) to get unloaded. The difference between using this message and calling pa_module_unload_request() is that the latter may only be called using the daemon mainloop, the message can be sent from other threads.

For information on how to use the inter-thread message passing system, see ?Messaging System, or while waiting for that to materialize, try Software/PulseAudio/Documentation/Developer/Threading.

Functions and macros

As mentioned earlier, the functions pa_core has associated with it, are not interesting for module writers. I'll list them here anyway for completeness's sake.
pa_core_new
  • Creates a new core that will use the given mainloop. The parameter shared is a boolean indicating whether the created mempool should be shared or not.
pa_core_check_quit
  • Updates the quit_event field, called by the client system when clients come and leave.
PA_DECLARE_CLASS(pa_core) in the header causes the following functions to become available (they are explained in the ?Object System page):
pa_core_isinstance
pa_core_cast
pa_core_ref
pa_core_unref
pa_core_refcnt
pa_core_assert_ref

And then there is the PA_CORE macro, that is just an alias for pa_core_cast.