Avoid loading OGG segments into memory

Uses the virtual IO interface for sndfile providing pread() as the
mechanism for loading data from the file handle. pread() makes it
possible to read bytes from the file without impacting the offset
which would be altered with normal fread()/fseek() or
dup()+fread()/fseek() calls.

By avoiding changing the shared offset values, pread() makes it
possible to avoid multi-threaded data races while avoiding the
modest memory usage of loading a single audio track to memory.

diff --git a/src/curses/ux_audio.c b/src/curses/ux_audio.c
index 30c32c9429ab509ac2482847a992859d60a55c4c..a178ffe769c468990fe7baa7f1cc62cb55f6d367 100644 (file)
--- a/src/curses/ux_audio.c
+++ b/src/curses/ux_audio.c
@@ -31,6 +31,7 @@
 #include <pthread.h>
 #include <semaphore.h>
 #include <assert.h>
+#include <unistd.h> //pread
 
 #ifdef USE_NCURSES_H
 #include <ncurses.h>
@@ -111,6 +112,13 @@ typedef struct {
     size_t   pos;
 } buf_t;
 
+typedef struct {
+    FILE    *file;
+    size_t   base_offset;
+    size_t   len;
+    size_t   pos;
+} file_reader_t;
+
 typedef struct {
     int (*process)(sound_stream_t *self, float *outl, float *outr, unsigned samples);
     void (*cleanup)(sound_stream_t *self);
@@ -127,7 +135,7 @@ typedef struct {
     int    repeats;    /* Total times to play the sample 1..n*/
     int    pos;
 
-    buf_t buf;
+    file_reader_t freader;
 } sound_stream_aiff_t;
 
 typedef struct {
@@ -179,7 +187,6 @@ static sound_engine_t frotz_audio;
  *                                                                    *
  * getfiledata          - get all bytes of a file after               *
  *                        the start point                             *
- * load_block_from_file - Load size bytes from current offset         *
  * make_id              - Create BLORB identifier                     *
  * get_type             - Get OGG/FORM/AIFF type                      *
  * limit                - x -> a <= x <= b                            *
@@ -198,16 +205,6 @@ getfiledata(FILE *fp, long *size)
     return(data);
 }
 
-static uint8_t *
-load_block_from_file(FILE *fp, long size)
-{
-    long offset = ftell(fp);
-    uint8_t *data = (uint8_t*)malloc(size);
-    fread(data, size, sizeof(uint8_t), fp);
-    fseek(fp, offset, SEEK_SET);
-    return data;
-}
-
 static
 int32_t make_id(uint8_t a, uint8_t b, uint8_t c, uint8_t d)
 {
@@ -455,39 +452,45 @@ cleanup_aiff(sound_stream_t *s)
     free(self->rsmp);
     sf_close(self->sndfile);
     free(self->floatbuffer);
-    free(self->buf.data);
 }
 
 static sf_count_t
 mem_snd_read(void *ptr_, sf_count_t size, void* datasource)
 {
     uint8_t *ptr = (uint8_t*)ptr_;
-    buf_t *buf = (buf_t *)datasource;
+    file_reader_t *fr = (file_reader_t *)datasource;
     size_t to_read = size;
-    size_t did_read = 0;
-    while(to_read > 0 && buf->pos < buf->len) {
-        *ptr++ = buf->data[buf->pos++];
-        did_read++;
-        to_read--;
+    size_t read_total = 0;
+    ssize_t did_read = 0;
+    while(to_read > 0) {
+        did_read = pread(fileno(fr->file), ptr, size, fr->pos+fr->base_offset);
+        if(did_read < 0)
+            return did_read;
+        else if(did_read == 0)
+            return read_total;
+        read_total += did_read;
+        fr->pos    += did_read;
+        ptr        += did_read;
+        to_read    -= did_read;
     }
-    return did_read;
+    return read_total;
 }
 
 static sf_count_t
 mem_snd_seek(sf_count_t offset, int whence, void *datasource) {
-    buf_t *buf = (buf_t *)datasource;
+    file_reader_t *fr = (file_reader_t *)datasource;
     int64_t pos = 0;
     if(whence == SEEK_SET)
         pos = offset;
     if(whence == SEEK_CUR)
         pos += offset;
     if(whence == SEEK_END)
-        pos = buf->len-offset;
-    if(pos >= (int64_t)buf->len)
-        pos = buf->len-1;
+        pos = fr->len-offset;
+    if(pos >= (int64_t)fr->len)
+        pos = fr->len-1;
     if(pos < 0)
         pos = 0;
-    buf->pos = pos;
+    fr->pos = pos;
 
     return 0;
 }
@@ -495,15 +498,15 @@ mem_snd_seek(sf_count_t offset, int whence, void *datasource) {
 
 static long
 mem_tell(void *datasource) {
-    buf_t *buf = (buf_t *)datasource;
-    return buf->pos;
+    file_reader_t *fr = (file_reader_t*)datasource;
+    return fr->pos;
 }
 
 static sf_count_t
 mem_get_filelen(void *datasource)
 {
-    buf_t *buf = (buf_t *)datasource;
-    return buf->len;
+    file_reader_t *fr = (file_reader_t*)datasource;
+    return fr->len;
 }
 
 static sound_stream_t *
@@ -520,8 +523,10 @@ load_aiff(FILE *fp, long startpos, long length, int id, float volume)
     aiff->sf_info.format = 0;
 
     fseek(fp, startpos, SEEK_SET);
-    aiff->buf.data = load_block_from_file(fp, length);
-    aiff->buf.len  = length;
+    aiff->freader.file        = fp;
+    aiff->freader.pos         = 0;
+    aiff->freader.len         = length;
+    aiff->freader.base_offset = startpos;
 
     SF_VIRTUAL_IO mem_cb = {
         .seek        = mem_snd_seek,
@@ -531,7 +536,7 @@ load_aiff(FILE *fp, long startpos, long length, int id, float volume)
         .write       = NULL
     };
 
-    aiff->sndfile = sf_open_virtual(&mem_cb, SFM_READ, &aiff->sf_info, &aiff->buf);
+    aiff->sndfile = sf_open_virtual(&mem_cb, SFM_READ, &aiff->sf_info, &aiff->freader);
     aiff->rsmp = resampler_init(aiff->sf_info.samplerate);
 
     aiff->floatbuffer = (float*)malloc(frotz_audio.buffer_size * aiff->sf_info.channels * sizeof(float));