try signalling invalidate on load error

to knock load ops out of cache

TODO

@@ -1,3 +1,11 @@
+- jpegload should put a pointer to the load operation inside the output image
+  somewhere
+
+  can we do this in the base class?
+
+  then the loaders can use this if they get a read error from the lib to
+  invalidate the load operation and knock it out of cache
+
 - I like the new int mask creator in reducev, can we use it in im_vips2imask()
   as well?
 

libvips/foreign/foreign.c

@@ -322,6 +322,10 @@
  * ]|
  */
 
+/* Usr this to link images to the load operations that made them. 
+ */
+static GQuark vips__foreign_load_operation = 0; 
+
 G_DEFINE_ABSTRACT_TYPE( VipsForeign, vips_foreign, VIPS_TYPE_OPERATION );
 
 static void
@@ -882,6 +886,13 @@ vips_foreign_load_build( VipsObject *object )
 
 	g_object_set( object, "out", vips_image_new(), NULL ); 
 
+	/* Note the load object on the output image. Loaders can use this to
+	 * signal invalidate if they hit a load error. See
+	 * vips_foreign_load_invalidate() below.
+	 */
+	g_object_set_qdata( G_OBJECT( load->out ), 
+		vips__foreign_load_operation, object ); 
+
 	vips_image_set_string( load->out, 
 		VIPS_META_LOADER, class->nickname );
 
@@ -1003,6 +1014,34 @@ vips_foreign_load_init( VipsForeignLoad *load )
 	load->access = VIPS_ACCESS_RANDOM;
 }
 
+/**
+ * Loaders can call this
+ */
+
+/**
+ * vips_foreign_load_invalidate:
+ * @image: image to invalidate
+ *
+ * Loaders can call this on the image they are making if they see a read error
+ * from the load library. It signals "invalidate" on the load operation and
+ * will cause it for be dropped from ache. 
+ *
+ * If we know a file will cause a read error, we don't want to cache the error
+ * operation, we want to make sure the image will really be opened again if our
+ * caller tries again. For example, a broken file might be replaced by a
+ * working one. 
+ */
+void
+vips_foreign_load_invalidate( VipsImage *image )
+{
+	VipsOperation *operation; 
+
+	if( (operation = g_object_get_qdata( G_OBJECT( image ), 
+		vips__foreign_load_operation )) ) {
+		vips_operation_invalidate( operation ); 
+	}
+}
+
 /* Abstract base class for image savers.
  */
 
@@ -1763,6 +1802,9 @@ vips_foreign_operation_init( void )
 #ifdef HAVE_OPENEXR
 	vips_foreign_load_openexr_get_type(); 
 #endif /*HAVE_OPENEXR*/
+
+	vips__foreign_load_operation = 
+		g_quark_from_static_string( "vips-foreign-load-operation" ); 
 }
 
 /**

libvips/foreign/jpeg2vips.c

@@ -959,8 +959,14 @@ read_jpeg_generate( VipsRegion *or,
 
 	/* Here for longjmp() from vips__new_error_exit().
 	 */
-	if( setjmp( jpeg->eman.jmp ) ) 
+	if( setjmp( jpeg->eman.jmp ) ) {
+		/* Signal invalidate on our load operation to force it from
+		 * cache. 
+		 */
+		vips_foreign_load_invalidate( or->im );
+
 		return( -1 );
+	}
 
 	for( y = 0; y < r->height; y++ ) {
 		JSAMPROW row_pointer[1];

libvips/include/vips/internal.h

@@ -246,6 +246,8 @@ typedef struct _VipsImagePixels {
 	gint64 npels;		/* Number of pels calculated so far */
 } VipsImagePixels;
 
+void vips_foreign_load_invalidate( VipsImage *image );
+
 #ifdef __cplusplus
 }
 #endif /*__cplusplus*/

libvips/iofuncs/header.c

@@ -402,6 +402,10 @@ vips_image_guess_format( const VipsImage *image )
 {
 	VipsBandFormat format;
 
+	/* Stop a compiler warning.
+	 */
+	format = VIPS_INTERPRETATION_MULTIBAND; 
+
 	switch( image->Type ) {
 	case VIPS_INTERPRETATION_B_W: 
 	case VIPS_INTERPRETATION_HISTOGRAM: