src/audio/SDL_sysaudio.h
author Ryan C. Gordon
Fri, 07 Oct 2016 14:35:25 -0400
changeset 10471 fd0bebfab510
parent 10467 be888d570cc8
child 10473 d6427519ca66
permissions -rw-r--r--
audio: threading and device hang improvements.

This tries to make SDL robust against device drivers that have hung up,
apps don't freeze in catastrophic (but not necessarily uncommon) conditions.

Now we detach the audio thread and let it clean up and don't care if it
never actually runs to completion.
     1 /*
     2   Simple DirectMedia Layer
     3   Copyright (C) 1997-2016 Sam Lantinga <slouken@libsdl.org>
     4 
     5   This software is provided 'as-is', without any express or implied
     6   warranty.  In no event will the authors be held liable for any damages
     7   arising from the use of this software.
     8 
     9   Permission is granted to anyone to use this software for any purpose,
    10   including commercial applications, and to alter it and redistribute it
    11   freely, subject to the following restrictions:
    12 
    13   1. The origin of this software must not be misrepresented; you must not
    14      claim that you wrote the original software. If you use this software
    15      in a product, an acknowledgment in the product documentation would be
    16      appreciated but is not required.
    17   2. Altered source versions must be plainly marked as such, and must not be
    18      misrepresented as being the original software.
    19   3. This notice may not be removed or altered from any source distribution.
    20 */
    21 #include "../SDL_internal.h"
    22 
    23 #ifndef _SDL_sysaudio_h
    24 #define _SDL_sysaudio_h
    25 
    26 #include "SDL_mutex.h"
    27 #include "SDL_thread.h"
    28 
    29 /* !!! FIXME: These are wordy and unlocalized... */
    30 #define DEFAULT_OUTPUT_DEVNAME "System audio output device"
    31 #define DEFAULT_INPUT_DEVNAME "System audio capture device"
    32 
    33 /* The SDL audio driver */
    34 typedef struct SDL_AudioDevice SDL_AudioDevice;
    35 #define _THIS   SDL_AudioDevice *_this
    36 
    37 /* Audio targets should call this as devices are added to the system (such as
    38    a USB headset being plugged in), and should also be called for
    39    for every device found during DetectDevices(). */
    40 extern void SDL_AddAudioDevice(const int iscapture, const char *name, void *handle);
    41 
    42 /* Audio targets should call this as devices are removed, so SDL can update
    43    its list of available devices. */
    44 extern void SDL_RemoveAudioDevice(const int iscapture, void *handle);
    45 
    46 /* Audio targets should call this if an opened audio device is lost while
    47    being used. This can happen due to i/o errors, or a device being unplugged,
    48    etc. If the device is totally gone, please also call SDL_RemoveAudioDevice()
    49    as appropriate so SDL's list of devices is accurate. */
    50 extern void SDL_OpenedAudioDeviceDisconnected(SDL_AudioDevice *device);
    51 
    52 
    53 /* This is the size of a packet when using SDL_QueueAudio(). We allocate
    54    these as necessary and pool them, under the assumption that we'll
    55    eventually end up with a handful that keep recycling, meeting whatever
    56    the app needs. We keep packing data tightly as more arrives to avoid
    57    wasting space, and if we get a giant block of data, we'll split them
    58    into multiple packets behind the scenes. My expectation is that most
    59    apps will have 2-3 of these in the pool. 8k should cover most needs, but
    60    if this is crippling for some embedded system, we can #ifdef this.
    61    The system preallocates enough packets for 2 callbacks' worth of data. */
    62 #define SDL_AUDIOBUFFERQUEUE_PACKETLEN (8 * 1024)
    63 
    64 /* Used by apps that queue audio instead of using the callback. */
    65 typedef struct SDL_AudioBufferQueue
    66 {
    67     Uint8 data[SDL_AUDIOBUFFERQUEUE_PACKETLEN];  /* packet data. */
    68     Uint32 datalen;  /* bytes currently in use in this packet. */
    69     Uint32 startpos;  /* bytes currently consumed in this packet. */
    70     struct SDL_AudioBufferQueue *next;  /* next item in linked list. */
    71 } SDL_AudioBufferQueue;
    72 
    73 typedef struct SDL_AudioDriverImpl
    74 {
    75     void (*DetectDevices) (void);
    76     int (*OpenDevice) (_THIS, void *handle, const char *devname, int iscapture);
    77     void (*ThreadInit) (_THIS); /* Called by audio thread at start */
    78     void (*WaitDevice) (_THIS);
    79     void (*PlayDevice) (_THIS);
    80     int (*GetPendingBytes) (_THIS);
    81     Uint8 *(*GetDeviceBuf) (_THIS);
    82     void (*WaitDone) (_THIS);
    83     int (*CaptureFromDevice) (_THIS, void *buffer, int buflen);
    84     void (*FlushCapture) (_THIS);
    85     void (*CloseDevice) (_THIS);
    86     void (*LockDevice) (_THIS);
    87     void (*UnlockDevice) (_THIS);
    88     void (*FreeDeviceHandle) (void *handle);  /**< SDL is done with handle from SDL_AddAudioDevice() */
    89     void (*Deinitialize) (void);
    90 
    91     /* !!! FIXME: add pause(), so we can optimize instead of mixing silence. */
    92 
    93     /* Some flags to push duplicate code into the core and reduce #ifdefs. */
    94     /* !!! FIXME: these should be SDL_bool */
    95     int ProvidesOwnCallbackThread;
    96     int SkipMixerLock;
    97     int HasCaptureSupport;
    98     int OnlyHasDefaultOutputDevice;
    99     int OnlyHasDefaultCaptureDevice;
   100     int AllowsArbitraryDeviceNames;
   101 } SDL_AudioDriverImpl;
   102 
   103 
   104 typedef struct SDL_AudioDeviceItem
   105 {
   106     void *handle;
   107     struct SDL_AudioDeviceItem *next;
   108     #if (defined(__GNUC__) && (__GNUC__ <= 2))
   109     char name[1];  /* actually variable length. */
   110     #else
   111     char name[];
   112     #endif
   113 } SDL_AudioDeviceItem;
   114 
   115 
   116 typedef struct SDL_AudioDriver
   117 {
   118     /* * * */
   119     /* The name of this audio driver */
   120     const char *name;
   121 
   122     /* * * */
   123     /* The description of this audio driver */
   124     const char *desc;
   125 
   126     SDL_AudioDriverImpl impl;
   127 
   128     /* A mutex for device detection */
   129     SDL_mutex *detectionLock;
   130     SDL_bool captureDevicesRemoved;
   131     SDL_bool outputDevicesRemoved;
   132     int outputDeviceCount;
   133     int inputDeviceCount;
   134     SDL_AudioDeviceItem *outputDevices;
   135     SDL_AudioDeviceItem *inputDevices;
   136 } SDL_AudioDriver;
   137 
   138 
   139 /* Streamer */
   140 typedef struct
   141 {
   142     Uint8 *buffer;
   143     int max_len;                /* the maximum length in bytes */
   144     int read_pos, write_pos;    /* the position of the write and read heads in bytes */
   145 } SDL_AudioStreamer;
   146 
   147 
   148 /* Define the SDL audio driver structure */
   149 struct SDL_AudioDevice
   150 {
   151     /* * * */
   152     /* Data common to all devices */
   153     SDL_AudioDeviceID id;
   154 
   155     /* The current audio specification (shared with audio thread) */
   156     SDL_AudioSpec spec;
   157 
   158     /* An audio conversion block for audio format emulation */
   159     SDL_AudioCVT convert;
   160 
   161     /* The streamer, if sample rate conversion necessitates it */
   162     int use_streamer;
   163     SDL_AudioStreamer streamer;
   164 
   165     /* Current state flags */
   166     SDL_atomic_t shutdown; /* true if we are signaling the play thread to end. */
   167     SDL_atomic_t enabled;  /* true if device is functioning and connected. */
   168     SDL_atomic_t paused;
   169     SDL_bool iscapture;
   170 
   171     /* Fake audio buffer for when the audio hardware is busy */
   172     Uint8 *fake_stream;
   173 
   174     /* A mutex for locking the mixing buffers */
   175     SDL_mutex *mixer_lock;
   176 
   177     /* A thread to feed the audio device */
   178     SDL_Thread *thread;
   179     SDL_threadID threadid;
   180 
   181     /* Queued buffers (if app not using callback). */
   182     SDL_AudioBufferQueue *buffer_queue_head; /* device fed from here. */
   183     SDL_AudioBufferQueue *buffer_queue_tail; /* queue fills to here. */
   184     SDL_AudioBufferQueue *buffer_queue_pool; /* these are unused packets. */
   185     Uint32 queued_bytes;  /* number of bytes of audio data in the queue. */
   186 
   187     /* * * */
   188     /* Data private to this driver */
   189     struct SDL_PrivateAudioData *hidden;
   190 
   191     void *handle;
   192 };
   193 #undef _THIS
   194 
   195 typedef struct AudioBootStrap
   196 {
   197     const char *name;
   198     const char *desc;
   199     int (*init) (SDL_AudioDriverImpl * impl);
   200     int demand_only;  /* 1==request explicitly, or it won't be available. */
   201 } AudioBootStrap;
   202 
   203 #endif /* _SDL_sysaudio_h */
   204 
   205 /* vi: set ts=4 sw=4 expandtab: */