seems to work for jpg anyway

try some tests next

ChangeLog

@@ -1,5 +1,6 @@
 1/5/16 started 8.4
 - many more wepsave options [Felix Bünemann]
+- kick load operations from cache on read error
 
 15/4/16 started 8.3.1
 - rename vips wrapper script, it was still vips-8.2, thanks Benjamin

libvips/foreign/foreign.c

@@ -791,6 +791,13 @@ vips_foreign_load_start( VipsImage *out, void *a, void *b )
 		 */
 		load->real->progress_signal = load->out;
 
+		/* Note the load object on the 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->real ), 
+			vips__foreign_load_operation, load ); 
+
 		if( class->load( load ) ||
 			vips_image_pio_input( load->real ) ) 
 			return( NULL );
@@ -886,13 +893,6 @@ 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 );
 
@@ -1036,6 +1036,10 @@ vips_foreign_load_invalidate( VipsImage *image )
 {
 	VipsOperation *operation; 
 
+#ifdef DEBUG
+	printf( "vips_foreign_load_invalidate: %p\n", image ); 
+#endif /*DEBUG*/
+
 	if( (operation = g_object_get_qdata( G_OBJECT( image ), 
 		vips__foreign_load_operation )) ) {
 		vips_operation_invalidate( operation ); 

libvips/foreign/jpeg2vips.c

@@ -243,6 +243,11 @@ readjpeg_new( VipsImage *out,
 	jpeg->y_pos = 0;
 	jpeg->autorotate = autorotate;
 
+	/* This is used by the error handlers to signal invalidate on the
+	 * output image.
+	 */
+        jpeg->cinfo.client_data = out;
+
 	/* jpeg_create_decompress() can fail on some sanity checks. Don't
 	 * readjpeg_free() since we don't want to jpeg_destroy_decompress().
 	 */
@@ -959,14 +964,8 @@ read_jpeg_generate( VipsRegion *or,
 
 	/* Here for longjmp() from vips__new_error_exit().
 	 */
-	if( setjmp( jpeg->eman.jmp ) ) {
-		/* Signal invalidate on our load operation to force it from
-		 * cache. 
-		 */
-		vips_foreign_load_invalidate( or->im );
-
+	if( setjmp( jpeg->eman.jmp ) ) 
 		return( -1 );
-	}
 
 	for( y = 0; y < r->height; y++ ) {
 		JSAMPROW row_pointer[1];

libvips/foreign/vips2jpeg.c

@@ -104,8 +104,8 @@
  */
 
 /*
-#define DEBUG
 #define VIPS_DEBUG
+#define DEBUG
  */
 
 #ifdef HAVE_CONFIG_H
@@ -122,9 +122,6 @@
 #include <setjmp.h>
 #include <math.h>
 
-#include <vips/vips.h>
-#include <vips/debug.h>
-
 #ifdef HAVE_EXIF
 #ifdef UNTAGGED_EXIF
 #include <exif-data.h>
@@ -139,6 +136,10 @@
 #endif /*UNTAGGED_EXIF*/
 #endif /*HAVE_EXIF*/
 
+#include <vips/vips.h>
+#include <vips/debug.h>
+#include <vips/internal.h>
+
 #include "jpeg.h"
 #include "vipsjpeg.h"
 
@@ -155,6 +156,12 @@ vips__new_output_message( j_common_ptr cinfo )
 #ifdef DEBUG
 	printf( "vips__new_output_message: \"%s\"\n", buffer );
 #endif /*DEBUG*/
+
+	/* This is run for things like file truncated. Signal invalidate to
+	 * force this op out of cache. 
+	 */
+        if( cinfo->client_data )
+		vips_foreign_load_invalidate( VIPS_IMAGE( cinfo->client_data ) );
 }
 
 /* New error_exit handler.

libvips/iofuncs/cache.c

@@ -46,6 +46,7 @@
 
 /*
 #define VIPS_DEBUG
+#define DEBUG
  */
 
 #ifdef HAVE_CONFIG_H
@@ -549,6 +550,10 @@ vips_cache_remove( VipsOperation *operation )
 	VipsOperationCacheEntry *entry = (VipsOperationCacheEntry *)
 		g_hash_table_lookup( vips_cache_table, operation );
 
+#ifdef DEBUG
+	printf( "vips_cache_remove: trimming %p\n", operation );
+#endif /*DEBUG*/
+
 	g_assert( entry ); 
 
 	if( entry->invalidate_id ) { 

libvips/iofuncs/operation.c

@@ -628,10 +628,10 @@ vips_operation_class_print_usage( VipsOperationClass *operation_class )
 void
 vips_operation_invalidate( VipsOperation *operation )
 {
-	/*
+#ifdef VIPS_DEBUG
 	printf( "vips_operation_invalidate: %p\n", operation ); 
 	vips_object_print_summary( VIPS_OBJECT( operation ) ); 
-	 */
+#endif /*VIPS_DEBUG*/
 
 	g_signal_emit( operation, vips_operation_signals[SIG_INVALIDATE], 0 );
 }