Introduce and use dt_dev_pixelpipe_piece_shutdown()

For a fast UI response when switching darkroom HQ processing mode or changing history (setting pipe
shutdown to DT_DEV_PIXELPIPE_STOP_NODES) we may use dt_dev_pixelpipe_set_shutdown() *while* processing
a module to enforce a clean pipe shutdown asap.

The pixelpipe tests for those UI induced shutdown requests for an early exit at safe locations.
Yet a few heavy processing modules with high number of iterations (most notably diffuse) can lead
to a significant delay until such a safe point has been reached.

With this commit they can test for a requested shutdown via dt_dev_pixelpipe_piece_shutdown() and
possibly stop iterating, cacheline integrity is kept by invalidating incorrect output.

Author: jenshannoschwalm

src/develop/pixelpipe_hb.c

@@ -1329,6 +1329,31 @@ static inline gboolean _module_pipe_stop(dt_dev_pixelpipe_t *pipe,
   return TRUE;
 }
 
+gboolean dt_dev_pixelpipe_piece_shutdown(dt_dev_pixelpipe_iop_t *piece)
+{
+  dt_dev_pixelpipe_t *pipe = piece->pipe;
+  const dt_dev_pixelpipe_stopper_t stopper = dt_atomic_get_int(&pipe->shutdown);
+  if(stopper <= DT_DEV_PIXELPIPE_STOP_NO)
+    return FALSE;
+
+  /* We check for any UI action requesting an early pipe shutdown as
+      DT_DEV_PIXELPIPE_STOP_NODES or DT_DEV_PIXELPIPE_STOP_HQ, we
+      - stop further processing the module thus it's output will be incorrect
+      - change the shutdown mode to the modules's iop_order so _module_pipe_stop()
+        can take care of cacheline validation.
+  */
+  if(stopper == DT_DEV_PIXELPIPE_STOP_NODES || stopper == DT_DEV_PIXELPIPE_STOP_HQ)
+  {
+    dt_print_pipe(DT_DEBUG_PIPE, "modify piece shutdown",
+      pipe, piece->module, pipe->devid, NULL, NULL, "%s",
+      dt_dev_pixelpipe_shutdown_to_str(stopper));
+
+    dt_atomic_set_int(&pipe->shutdown, piece->module->iop_order);
+  }
+
+  return TRUE;
+}
+
 void dt_dev_prepare_piece_cfa(dt_dev_pixelpipe_iop_t *piece, const dt_iop_roi_t *roi)
 {
   dt_iop_module_t *module = piece->module;

src/develop/pixelpipe_hb.h

@@ -423,6 +423,9 @@ void dt_dev_pixelpipe_disable_after(dt_dev_pixelpipe_t *pipe, const char *op);
 // disable given op and all that comes before it in the pipe:
 void dt_dev_pixelpipe_disable_before(dt_dev_pixelpipe_t *pipe, const char *op);
 
+// pieces can test for a pipe shutdown request within module->process().
+gboolean dt_dev_pixelpipe_piece_shutdown(dt_dev_pixelpipe_iop_t *piece);
+
 // helper function to pass a raster mask through a (so far) processed pipe
 float *dt_dev_get_raster_mask(dt_dev_pixelpipe_iop_t *piece,
                               const struct dt_iop_module_t *raster_mask_source,

src/iop/diffuse.c

@@ -1414,7 +1414,7 @@ void process(dt_iop_module_t *self,
     in = temp1;
   }
 
-  for(int it = 0; it < iterations; it++)
+  for(int it = 0; it < iterations && !dt_dev_pixelpipe_piece_shutdown(piece); it++)
   {
     if(it == 0)
     {
@@ -1680,7 +1680,7 @@ int process_cl(dt_iop_module_t *self,
     in = temp1;
   }
 
-  for(int it = 0; it < iterations && err == CL_SUCCESS; it++)
+  for(int it = 0; it < iterations && err == CL_SUCCESS && !dt_dev_pixelpipe_piece_shutdown(piece); it++)
   {
     if(it == 0)
     {