audio_output/amem.c: multiple buffers

Support multiple buffers appended after the shared header. Each buffer has
a small header that keeps the number of buffers in the samples buffer.

modules/audio_output/amem.c

@@ -91,6 +91,12 @@ static const int format_int[] = { VLC_CODEC_U8,
                                   VLC_CODEC_SPDIFL };
 
 /* Shared memory header structure */
+typedef struct
+{
+    unsigned int i_nb_samples;    /* number of samples in buffer */
+    void         *samples;        /* samples buffer */
+} amem_buffer_t;
+
 typedef struct
 {
     vlc_sem_t     sem; /* handle to semaphore */
@@ -103,14 +109,16 @@ typedef struct
     unsigned int  i_frame_length;
     unsigned      i_bitspersample;
     unsigned      i_blockalign;
-    uint8_t      i_channels;
+    unsigned      i_channels;
 #endif
 
+    unsigned int  i_max_samples;   /* maximum samples per buffer */
     unsigned int  i_read_samples;  /* total samples read */
     unsigned int  i_write_samples; /* total samples written */
-    unsigned int i_max_samples;   /* maximum samples in buffer */
-    unsigned int i_nb_samples;    /* number of samples in buffer */
-    void         *samples;        /* buffer of samples */
+    /* if i_buf_write == i_buffers, then it will wrap around */
+    unsigned int  i_read;    /* buffer being read */
+    unsigned int  i_write;   /* buffer being written */
+    unsigned int  i_buffers; /* number of sample buffers used */
 } amem_shared_t;
 
 /* Private structure */
@@ -134,7 +142,7 @@ static int  Open (vlc_object_t *);
 static void Close(vlc_object_t *);
 static void Play (aout_instance_t *);
 
-static int SetupSharedMem(aout_instance_t *);
+static int SetupSharedMem(aout_instance_t *, unsigned int);
 static void ExitSharedMem(aout_instance_t *);
 
 /*
@@ -216,7 +224,18 @@ static void amem_sem_destroy(vlc_sem_t *sem)
 #endif
 }
 
-static int amem_shmem_create(aout_instance_t *aout, ssize_t len)
+static amem_buffer_t *amem_buffer_get(aout_instance_t *aout, unsigned int index)
+{
+    aout_sys_t *sys = (aout_sys_t *)aout->output.p_sys;
+    amem_buffer_t *buffer = NULL;
+
+    size_t buflen = sizeof(amem_buffer_t) + aout->output.i_nb_samples * aout->output.output.i_bitspersample;
+    buffer = (amem_buffer_t *)((uint8_t*)sys->header + sizeof(amem_shared_t) + index * buflen);
+    buffer->samples = ((uint8_t *)buffer + sizeof(amem_buffer_t));
+    return buffer;
+}
+
+static int amem_shmem_create(aout_instance_t *aout, unsigned int i_buffers, ssize_t len)
 {
     aout_sys_t *sys = (aout_sys_t *)aout->output.p_sys;
 
@@ -273,7 +292,17 @@ static int amem_shmem_create(aout_instance_t *aout, ssize_t len)
     }
 #endif
 
-    sys->header->samples = sys->header + sizeof(amem_shared_t);
+    /* setup pointers in shared structures */
+    sys->header->i_buffers = i_buffers;
+    for (unsigned int i = 0; i < sys->header->i_buffers; i++)
+    {
+        amem_buffer_t *buffer = amem_buffer_get(aout, i);
+        if (buffer)
+        {
+            buffer->i_nb_samples = 0;
+            memset(buffer->samples, 0, (sys->header->i_max_samples * sys->header->i_bitspersample));
+        }
+    }
 
     /* initialize unamed semaphore */
     amem_sem_init(&sys->header->sem, 1);
@@ -282,7 +311,7 @@ static int amem_shmem_create(aout_instance_t *aout, ssize_t len)
     return VLC_SUCCESS;
 }
 
-static int amem_shmem_open(aout_instance_t *aout, ssize_t len)
+static int amem_shmem_open(aout_instance_t *aout, unsigned int i_buffers, ssize_t len)
 {
     aout_sys_t *sys = (aout_sys_t *)aout->output.p_sys;
 
@@ -333,7 +362,15 @@ static int amem_shmem_open(aout_instance_t *aout, ssize_t len)
         return VLC_EGENERIC;
     }
 #endif
-    sys->header->samples = sys->header + sizeof(amem_shared_t);
+
+    /* setup pointers in shared structures */
+    sys->header->i_buffers = i_buffers;
+    for (unsigned int i = 0; i < sys->header->i_buffers; i++)
+    {
+        amem_buffer_t *buffer = amem_buffer_get(aout, i);
+        if (buffer)
+            buffer->i_nb_samples = 0;
+    }
 
     msg_Dbg(aout, "shared memory opened");
     return VLC_SUCCESS;
@@ -353,8 +390,8 @@ static void amem_shmem_close(aout_instance_t *aout)
     /* Determine shared memory size */
     if (sys->header != MAP_FAILED)
     {
-        ssize_t len = sizeof(amem_shared_t) + aout->output.i_nb_samples
-                    * aout->output.output.i_bitspersample;
+        ssize_t len = sizeof(amem_shared_t) + sys->header->i_buffers * (sizeof(amem_buffer_t)
+                       + aout->output.i_nb_samples * aout->output.output.i_bitspersample);
         if (munmap(sys->header, len) < 0)
         {
             msg_Err(aout, "failed unmapping shared memory (%m)");
@@ -379,13 +416,13 @@ static void amem_shmem_header(aout_instance_t *aout)
 #if defined(_WIN32_WINNT) || defined(WIN32)
     uint16_t tag = 0;
     fourcc_to_wf_tag(aout->output.output.i_format, &tag);
-    sys->header->wave.wFormatTag = tag;
-    sys->header->wave.nChannels = aout->output.output.i_channels;
-    sys->header->wave.nSamplesPerSec = aout->output.output.i_rate * aout->output.i_nb_samples;
-    //sys->header->wave.nAvgBytesPerSec = ;
-    sys->header->wave.nBlockAlign = aout->output.output.i_blockalign;
-    sys->header->wave.wBitsPerSample = aout->output.output.i_bitspersample;
-    sys->header->wave.cbSize = 0; /* No additional format metadata */
+    header->wave.wFormatTag = tag;
+    header->wave.nChannels = aout->output.output.i_channels;
+    header->wave.nSamplesPerSec = aout->output.output.i_rate * aout->output.i_nb_samples;
+    //header->wave.nAvgBytesPerSec = ;
+    header->wave.nBlockAlign = aout->output.output.i_blockalign;
+    header->wave.wBitsPerSample = aout->output.output.i_bitspersample;
+    header->wave.cbSize = 0; /* No additional format metadata */
 #else
     header->i_format = aout->output.output.i_format;
     header->i_bitspersample = aout->output.output.i_bitspersample;
@@ -396,13 +433,9 @@ static void amem_shmem_header(aout_instance_t *aout)
     header->i_blockalign = aout->output.output.i_blockalign;
 #endif
 
-    header->i_read_samples = 0;
-    header->i_write_samples = 0;
+    header->i_read = header->i_write = 0;
+    header->i_read_samples = header->i_write_samples = 0;
     header->i_max_samples = aout->output.i_nb_samples;
-    header->i_nb_samples = 0;
-
-    memset(header->samples, 0, (aout->output.i_nb_samples *
-                                aout->output.output.i_bitspersample));
 
     amem_sem_post(&header->sem);
 }
@@ -412,21 +445,25 @@ static int amem_shmem_write(aout_instance_t *aout, aout_buffer_t *p_buffer)
     aout_sys_t *sys = (aout_sys_t *)aout->output.p_sys;
 
     amem_sem_wait(&sys->header->sem);
-
-    /* FIXME: do not assume we can fill the entire buffer */
+    amem_buffer_t *buf = amem_buffer_get(aout, sys->header->i_write);
+    if (buf == NULL)
+    {
+        amem_sem_post(&sys->header->sem);
+        return VLC_EGENERIC;
+    }
     assert(p_buffer->i_nb_samples <= sys->header->i_max_samples);
 
 #if defined(_WIN32_WINNT) || defined(WIN32)
-    CopyMemory((PVOID)sys->header->samples, data->p_buffer, data->i_buffer);
+    CopyMemory((PVOID)buf->samples, p_buffer->p_buffer, p_buffer->i_buffer);
 #else
-    memcpy(sys->header->samples, p_buffer->p_buffer, p_buffer->i_buffer);
+    memcpy(buf->samples, p_buffer->p_buffer, p_buffer->i_buffer);
 #endif
 
-    sys->header->i_nb_samples = p_buffer->i_nb_samples;
-    sys->header->i_write_samples += p_buffer->i_nb_samples;
+    buf->i_nb_samples = p_buffer->i_nb_samples;
 
+    sys->header->i_write_samples += p_buffer->i_nb_samples;
+    sys->header->i_write = (sys->header->i_write + 1) % sys->header->i_buffers;
     amem_sem_post(&sys->header->sem);
-
     return VLC_SUCCESS;
 }
 
@@ -442,6 +479,10 @@ static int amem_shmem_write(aout_instance_t *aout, aout_buffer_t *p_buffer)
 #define ACHANS_LONGTEXT N_( \
     "Number of audio channels in the audio output." )
 
+#define ABUFS_TEXT N_("Number of shared audio buffers")
+#define ABUFS_LONGTEXT N_( \
+    "Number of shared audio buffers to use.")
+
 #define AFORMAT_TEXT N_("Output format")
 #define AFORMAT_LONGTEXT N_( \
     "One of \"u8\", \"s8\", \"u16\", \"s16\", " \
@@ -471,6 +512,8 @@ vlc_module_begin()
     add_string( AMEM_CFG_PREFIX "format", "s16", NULL, AFORMAT_TEXT,
                 AFORMAT_LONGTEXT, true )
         change_string_list( format_list, 0, 0 )
+    add_integer( AMEM_CFG_PREFIX "buffers", 2, NULL, ABUFS_TEXT,
+                 ABUFS_LONGTEXT, false )
     add_integer( AMEM_CFG_PREFIX "channels", 2, NULL, ACHANS_TEXT,
                  ACHANS_LONGTEXT, false )
         change_integer_range( 0, CHANNELS_MAX )
@@ -557,8 +600,15 @@ static int Open(vlc_object_t *p_this)
             pi_channels_maps[i_channels];
     }
 
+    int i_buffers = var_CreateGetInteger(aout, AMEM_CFG_PREFIX "buffers");
+    if (i_buffers < 1)
+    {
+        msg_Err(aout, "insufficient shared audio buffers requested");
+        return VLC_EGENERIC;
+    }
+
     /* Setup shared memory connection */
-    if (SetupSharedMem(aout) != VLC_SUCCESS)
+    if (SetupSharedMem(aout, i_buffers) != VLC_SUCCESS)
     {
         Close(p_this);
         return VLC_EGENERIC;
@@ -602,14 +652,13 @@ static void Play(aout_instance_t *aout)
 /*****************************************************************************
  * Shared Memory
  *****************************************************************************/
-static int SetupSharedMem(aout_instance_t *aout)
+static int SetupSharedMem(aout_instance_t *aout, unsigned int i_buffers)
 {
     aout_sys_t *sys = (aout_sys_t *)aout->output.p_sys;
 
     /* Determine shared memory size */
-    ssize_t len = sizeof(amem_shared_t) + aout->output.i_nb_samples
-                    * aout->output.output.i_bitspersample;
-
+    ssize_t len = sizeof(amem_shared_t) + i_buffers * (sizeof(amem_buffer_t)
+                       + aout->output.i_nb_samples * aout->output.output.i_bitspersample);
     if (*sys->psz_name != '/')
     {
         msg_Err(aout, "invalid shared segment name (does not begin with /)");
@@ -622,7 +671,7 @@ static int SetupSharedMem(aout_instance_t *aout)
         return VLC_EGENERIC;
     }
 
-    if (amem_shmem_open(aout, len) != VLC_SUCCESS)
+    if (amem_shmem_open(aout, i_buffers, len) != VLC_SUCCESS)
         return VLC_EGENERIC;
 
     /* Fill header struct */