Fix issue in display list Cache

The commit fc05b51c2b198dcc5553f6de1b8fb0e22e7d28ae cleaned up a few issues in the
display list cache but it introduced issues when multiple threads are using the lists.
In particular one thread could be using a list at the tail of the cache list, while
another thread is adding one to the cache, and removing the entry at the tail.  The
solution is to make sure the ref count of the list is incremented when someone is using the list
and making sure that it gets decremented when they are done with the list.

1 files changed, 15 insertions, 0 deletions

diff --git a/platform/windows/mupdfwinrt/muctx.cpp b/platform/windows/mupdfwinrt/muctx.cpp
index fbcb01f3..e51ea403 100644
--- a/platform/windows/mupdfwinrt/muctx.cpp
+++ b/platform/windows/mupdfwinrt/muctx.cpp
@@ -531,6 +531,21 @@ fz_display_list * muctx::CreateDisplayList(int page_num, int *width, int *height
 	return dlist;
 }
 
+void muctx::ReleaseDisplayLists(void *opdlist, void *opannotlist)
+{
+	fz_display_list *dlist = (fz_display_list*) opdlist;
+	fz_display_list *annotlist = (fz_display_list*) opannotlist;
+
+	if (dlist != NULL)
+	{
+		fz_drop_display_list(mu_ctx, dlist);
+	}
+	if (annotlist != NULL)
+	{
+		fz_drop_display_list(mu_ctx, annotlist);
+	}
+}
+
 /* A special version which will create the display list AND get the information
    that we need for various text selection tasks */
 fz_display_list * muctx::CreateDisplayListText(int page_num, int *width, int *height,