seq debug notes

TODO

@@ -1,3 +1,59 @@
+- try
+
+	$ vips shrink Chicago.png x.v 230 230
+	** VIPS:ERROR:vipspng.c:432:png2vips_generate: assertion failed: (r->top == read->y_pos)
+	Aborted (core dumped)
+
+$ vips shrink Chicago.png x.v 230 230 --vips-progress
+vips_sequential_class_init
+vips x.v: 127 x 18 pixels, 4 threads, 127 x 1 tiles, 1280 lines in buffer
+vips_sequential_build
+
+thread 0x24a7cf0 request for 230 lines, start line 0
+thread 0x24a7cf0 has lock ...
+thread 0x24a7cf0 reading ...
+
+thread 0x24a7ca0 request for 230 lines, start line 230
+
+thread 0x24a7d40 request for 230 lines, start line 460
+
+thread 0x24a7d90 request for 230 lines, start line 690
+
+thread 0x24a7cf0 updating y_pos to 230 and waking stalled
+thread 0x24a7cf0 unlocking ...
+
+thread 0x24a7ca0 has lock ...
+thread 0x24a7ca0 reading ...
+
+thread 0x24a7cf0 request for 230 lines, start line 0
+
+thread 0x24a7ca0 updating y_pos to 460 and waking stalled
+thread 0x24a7ca0 unlocking ...
+
+thread 0x24a7d40 has lock ...
+thread 0x24a7d40 reading ...
+
+thread 0x24a7ca0 request for 230 lines, start line 230
+
+thread 0x24a7d40 updating y_pos to 690 and waking stalled
+thread 0x24a7d40 unlocking ...
+
+thread 0x24a7d90 has lock ...
+thread 0x24a7d90 reading ...
+
+thread 0x24a7d40 request for 230 lines, start line 460
+
+thread 0x24a7d90 updating y_pos to 920 and waking stalled
+thread 0x24a7d90 unlocking ...
+
+thread 0x24a7cf0 has lock ...
+thread 0x24a7cf0 reading ...
+**
+VIPS:ERROR:vipspng.c:432:png2vips_generate: assertion failed: (r->top ==
+read->y_pos)
+Aborted (core dumped)
+
+
 - move other/im_makexy.c into copnversion? should sit with bvips_black()?
 
 - look at