avfilter/asubprocess: improve buffering code

Rather than allocating a new sub buffer for every read, fill up remaining
space of the last subbuffer if available.
Signed-off-by: Stefan Westerfeld <stefan@space.twc.de>

libavfilter/af_asubprocess.c

@@ -27,7 +27,7 @@
 #include <stdbool.h>
 #include <string.h>
 
-#define BUFFER_SIZE 4096
+#define BUFFER_SIZE 1024 * 128
 
 typedef struct SPB
 {
@@ -162,23 +162,33 @@ sp_write (SP *sp, char *buffer, int count)
                 offset += rc;
                 count -= rc;
             }
+            else if (rc < 0 && errno != EAGAIN && errno != EINTR)
+            {
+                perror ("write to subprocess failed");
+                return AVERROR_EXTERNAL;
+            }
         }
         if (fds[1].revents & (POLLIN | POLLHUP))
         {
-            SPB *spb = spb_new();
-            int rc = read(sp->output_pipe, spb->data, sizeof (spb->data));
+            SPB *last;
+            int rc;
+
+            if (!sp->out_buffers)
+                sp->out_buffers = spb_new();
+
+            last = sp->out_buffers;
+            while (last->next)
+                last = last->next;
+
+            if (last->count == sizeof (last->data))
+            {
+                last->next = spb_new();
+                last = last->next;
+            }
+            rc = read(sp->output_pipe, last->data + last->count, sizeof (last->data) - last->count);
             if (rc > 0)
             {
-                spb->count = rc;
-                if (!sp->out_buffers)
-                    sp->out_buffers = spb;
-                else
-                {
-                    SPB *last = sp->out_buffers;
-                    while (last->next)
-                      last = last->next;
-                    last->next = spb;
-                }
+                last->count += rc;
             }
             else if (rc == 0)
             {
@@ -190,6 +200,11 @@ sp_write (SP *sp, char *buffer, int count)
                     return AVERROR_EXTERNAL;
                 return 0;
             }
+            else if (errno != EAGAIN && errno != EINTR)
+            {
+                perror ("read from subprocess failed");
+                return AVERROR_EXTERNAL;
+            }
         }
     } while (count);
     return 0;