AudioPolicyInterface: add note on nullptr checks

// ----------------------------------------------------------------------------

// The AudioPolicyInterface and AudioPolicyClientInterface classes define the communication interfaces

// between the platform specific audio policy manager and Android generic audio policy manager.

// The platform specific audio policy manager must implement methods of the AudioPolicyInterface class.

// The AudioPolicyInterface and AudioPolicyClientInterface classes define the communication

// interfaces between the platform specific audio policy manager and Android generic audio policy

// manager.

// The platform specific audio policy manager must implement methods of the AudioPolicyInterface

// class.

// This implementation makes use of the AudioPolicyClientInterface to control the activity and

// configuration of audio input and output streams.

//

// The platform specific audio policy manager is in charge of the audio routing and volume control

// policies for a given platform.

// The main roles of this module are:

//   - keep track of current system state (removable device connections, phone state, user requests...).

//   System state changes and user actions are notified to audio policy manager with methods of the AudioPolicyInterface.

//   - keep track of current system state (removable device connections, phone state,

//   user requests...).

//   System state changes and user actions are notified to audio policy manager with methods of the

//   AudioPolicyInterface.

//   - process getOutput() queries received when AudioTrack objects are created: Those queries

//   return a handler on an output that has been selected, configured and opened by the audio policy manager and that

//   must be used by the AudioTrack when registering to the AudioFlinger with the createTrack() method.

//   When the AudioTrack object is released, a putOutput() query is received and the audio policy manager can decide

//   to close or reconfigure the output depending on other streams using this output and current system state.

//   - similarly process getInput() and putInput() queries received from AudioRecord objects and configure audio inputs.

//   - process volume control requests: the stream volume is converted from an index value (received from UI) to a float value

//   applicable to each output as a function of platform specific settings and current output route (destination device). It

//   also make sure that streams are not muted if not allowed (e.g. camera shutter sound in some countries).

//   return a handler on an output that has been selected, configured and opened by the audio

//   policy manager and that must be used by the AudioTrack when registering to the AudioFlinger

//   with the createTrack() method.

//   When the AudioTrack object is released, a putOutput() query is received and the audio policy

//   manager can decide to close or reconfigure the output depending on other streams using this

//   output and current system state.

//   - similarly process getInput() and putInput() queries received from AudioRecord objects and

//   configure audio inputs.

//   - process volume control requests: the stream volume is converted from an index value

//   (received from UI) to a float value applicable to each output as a function of platform

//   specificsettings and current output route (destination device). It also make sure that streams

//   are not muted if not allowed (e.g. camera shutter sound in some countries).

//

// The platform specific audio policy manager is provided as a shared library by platform vendors (as for libaudio.so)

// and is linked with libaudioflinger.so

// The platform specific audio policy manager is provided as a shared library by platform vendors

// (as for libaudio.so) and is linked with libaudioflinger.so

//

// NOTE: by convention, the implementation of the AudioPolicyInterface in AudioPolicyManager does

// not have to perform any nullptr check on input arguments: The caller of this API is

// AudioPolicyService running in the same process and in charge of validating arguments received

// from incoming binder calls before calling AudioPolicyManager.

//    Audio Policy Manager Interface

class AudioPolicyInterface

                                        audio_port_handle_t *portId,

                                        std::vector<audio_io_handle_t> *secondaryOutputs,

                                        output_type_t *outputType) = 0;

    // indicates to the audio policy manager that the output starts being used by corresponding stream.

    // indicates to the audio policy manager that the output starts being used by corresponding

    // stream.

    virtual status_t startOutput(audio_port_handle_t portId) = 0;

    // indicates to the audio policy manager that the output stops being used by corresponding stream.

    // indicates to the audio policy manager that the output stops being used by corresponding

    // stream.

    virtual status_t stopOutput(audio_port_handle_t portId) = 0;

    // releases the output, return true if the output descriptor is reopened.

    virtual bool releaseOutput(audio_port_handle_t portId) = 0;

    // Audio output Control functions

    //

    // opens an audio output with the requested parameters. The parameter values can indicate to use the default values

    // in case the audio policy manager has no specific requirements for the output being opened.

    // When the function returns, the parameter values reflect the actual values used by the audio hardware output stream.

    // The audio policy manager can check if the proposed parameters are suitable or not and act accordingly.

    // opens an audio output with the requested parameters. The parameter values can indicate to

    // use the default values in case the audio policy manager has no specific requirements for the

    // output being opened.

    // When the function returns, the parameter values reflect the actual values used by the audio

    // hardware output stream.

    // The audio policy manager can check if the proposed parameters are suitable or not and act

    // accordingly.

    virtual status_t openOutput(audio_module_handle_t module,

                                audio_io_handle_t *output,

                                audio_config_t *halConfig,

                                const sp<DeviceDescriptorBase>& device,

                                uint32_t *latencyMs,

                                audio_output_flags_t flags) = 0;

    // creates a special output that is duplicated to the two outputs passed as arguments. The duplication is performed by

    // a special mixer thread in the AudioFlinger.

    virtual audio_io_handle_t openDuplicateOutput(audio_io_handle_t output1, audio_io_handle_t output2) = 0;

    // creates a special output that is duplicated to the two outputs passed as arguments.

    // The duplication is performed by a special mixer thread in the AudioFlinger.

    virtual audio_io_handle_t openDuplicateOutput(audio_io_handle_t output1,

                                                  audio_io_handle_t output2) = 0;

    // closes the output stream

    virtual status_t closeOutput(audio_io_handle_t output) = 0;

    // suspends the output. When an output is suspended, the corresponding audio hardware output stream is placed in

    // standby and the AudioTracks attached to the mixer thread are still processed but the output mix is discarded.

    // suspends the output. When an output is suspended, the corresponding audio hardware output

    // stream is placed in standby and the AudioTracks attached to the mixer thread are still

    // processed but the output mix is discarded.

    virtual status_t suspendOutput(audio_io_handle_t output) = 0;

    // restores a suspended output.

    virtual status_t restoreOutput(audio_io_handle_t output) = 0;

    // misc control functions

    //

    // set a stream volume for a particular output. For the same user setting, a given stream type can have different volumes

    // set a stream volume for a particular output. For the same user setting, a given stream type

    // can have different volumes

    // for each output (destination device) it is attached to.

    virtual status_t setStreamVolume(audio_stream_type_t stream, float volume, audio_io_handle_t output, int delayMs = 0) = 0;

    virtual status_t setStreamVolume(audio_stream_type_t stream, float volume,

                                     audio_io_handle_t output, int delayMs = 0) = 0;

    // invalidate a stream type, causing a reroute to an unspecified new output

    virtual status_t invalidateStream(audio_stream_type_t stream) = 0;

    // function enabling to send proprietary informations directly from audio policy manager to audio hardware interface.

    virtual void setParameters(audio_io_handle_t ioHandle, const String8& keyValuePairs, int delayMs = 0) = 0;

    // function enabling to receive proprietary informations directly from audio hardware interface to audio policy manager.

    // function enabling to send proprietary informations directly from audio policy manager to

    // audio hardware interface.

    virtual void setParameters(audio_io_handle_t ioHandle, const String8& keyValuePairs,

                               int delayMs = 0) = 0;

    // function enabling to receive proprietary informations directly from audio hardware interface

    // to audio policy manager.

    virtual String8 getParameters(audio_io_handle_t ioHandle, const String8& keys) = 0;

    // set down link audio volume.

    // These are the signatures of createAudioPolicyManager/destroyAudioPolicyManager

    // methods respectively, expected by AudioPolicyService, needs to be exposed by

    // libaudiopolicymanagercustom.

    using CreateAudioPolicyManagerInstance = AudioPolicyInterface* (*)(AudioPolicyClientInterface*);

    using CreateAudioPolicyManagerInstance =

            AudioPolicyInterface* (*)(AudioPolicyClientInterface*);

    using DestroyAudioPolicyManagerInstance = void (*)(AudioPolicyInterface*);

} // namespace android