avfilter/asubprocess: maintain a list of unused buffers

Signed-off-by: Stefan Westerfeld <stefan@space.twc.de>

libavfilter/af_asubprocess.c

@@ -39,6 +39,7 @@ typedef struct SP
     int     input_pipe;
     int     output_pipe;
     SPB    *out_buffers;
+    SPB    *unused_buffers;
     int     pid;
     size_t  input_count;
     bool    done;
@@ -68,10 +69,16 @@ typedef struct AndioWMarkContext {
     FFFrameQueue  frame_queue;
 } ASubProcessContext;
 
-// =============================================
-static SPB *spb_new(void)
+static SPB *spb_new(AVFilterContext *ctx)
 {
-    SPB *spb = av_malloc(sizeof(SPB));
+    ASubProcessContext *s = ctx->priv;
+    SPB *spb = s->sp->unused_buffers;
+    if (spb) {
+        s->sp->unused_buffers = spb->next;
+    }
+    else {
+        spb = av_malloc(sizeof(SPB));
+    }
 
     spb->next = NULL;
     spb->offset = 0;
@@ -178,7 +185,8 @@ sp_read(SP *sp, char *buffer, int count)
             return;
 
         sp->out_buffers = spb->next;
-        av_free(spb);
+        spb->next = sp->unused_buffers;
+        sp->unused_buffers = spb;
         spb = sp->out_buffers;
     }
 }
@@ -306,14 +314,14 @@ sp_write(AVFilterContext *ctx, char *buffer, int count)
             int rc, ret;
 
             if (!sp->out_buffers)
-                sp->out_buffers = spb_new();
+                sp->out_buffers = spb_new(ctx);
 
             last = sp->out_buffers;
             while (last->next)
                 last = last->next;
 
             if (last->count == sizeof(last->data)) {
-                last->next = spb_new();
+                last->next = spb_new(ctx);
                 last = last->next;
             }
             rc = read(sp->output_pipe, last->data + last->count, sizeof(last->data) - last->count);