fix a race in tiled tiffload and pdfload

We weer minimising sources in the ::minimise handler, but this is called
outside the lock that protects _generate. This patch removes minimise in
this case.

See https://github.com/kleisauke/net-vips/issues/53

ChangeLog

@@ -3,6 +3,7 @@
   will break the loader priority system
 - fix thumbnail autorot [janko]
 - fix a warning with magicksave with no delay array [chregu]
+- fix a race in tiled tiff load [kleisauke]
 
 20/6/19 started 8.9.0
 - add vips_image_get/set_array_int()

libvips/foreign/pdfload.c

@@ -362,18 +362,6 @@ vips_foreign_load_pdf_header( VipsForeignLoad *load )
 	return( 0 );
 }
 
-static void
-vips_foreign_load_pdf_minimise( VipsObject *object, VipsForeignLoadPdf *pdf )
-{
-	VipsForeignLoadPdfClass *class = VIPS_FOREIGN_LOAD_PDF_GET_CLASS( pdf );
-
-#ifdef DEBUG
-	printf( "vips_foreign_load_pdf_minimise: %p\n", pdf );
-#endif /*DEBUG*/
-
-	class->close( pdf ); 
-}
-
 static int
 vips_foreign_load_pdf_generate( VipsRegion *or, 
 	void *seq, void *a, void *b, gboolean *stop )
@@ -472,10 +460,9 @@ vips_foreign_load_pdf_load( VipsForeignLoad *load )
 	 */
 	t[0] = vips_image_new(); 
 
-	/* Close input immediately at end of read.
+	/* Don't minimise on ::minimise (end of computation): we support 
+	 * threaded read, and minimise will happen outside the cache lock.
 	 */
-	g_signal_connect( t[0], "minimise", 
-		G_CALLBACK( vips_foreign_load_pdf_minimise ), pdf ); 
 
 	vips_foreign_load_pdf_set_image( pdf, t[0] ); 
 	if( vips_image_generate( t[0], 

libvips/foreign/tiff2vips.c

@@ -507,7 +507,13 @@ rtiff_close_cb( VipsObject *object, Rtiff *rtiff )
 static void
 rtiff_minimise_cb( VipsImage *image, Rtiff *rtiff )
 {
-	if( rtiff->source )
+	/* We must not minimised tiled images. These can be read from many
+	 * threads, and this minimise handler is not inside the lock that our
+	 * tilecache is using to guarantee single-threaded access to our
+	 * source.
+	 */
+	if( !rtiff->header.tiled &&
+		rtiff->source )
 		vips_source_minimise( rtiff->source );
 }