possible race in vips_sink_*() progress reporting

[jcupitt]

This program:

/* compile with
 *
 *      gcc -g -Wall race.c `pkg-config vips --cflags --libs`
 */

#include <vips/vips.h>

static void
posteval_cb( VipsImage *image, VipsProgress *progress, void *client )
{
        printf( "posteval_cb: percent = %d\n",
                progress->percent );
}

int
main( int argc, char **argv )
{       
        double avg;
        VipsImage *image;

        VIPS_INIT( argv[0] );
        
        vips_xyz( &image, 10, 1000, NULL );
        
        vips_image_set_progress( image, TRUE );
        g_signal_connect( image, "posteval", G_CALLBACK( posteval_cb ), NULL );
        
        printf( "testing vips_sink()\n" );
        vips_avg( image, &avg, NULL );
        printf( "sum = %ld\n",  
                (gint64) (avg * image->Xsize * image->Ysize * image->Bands) );

        printf( "testing vips_sink_memory()\n" );
        VipsImage *mem;
        mem = vips_image_copy_memory( image );
        VIPS_UNREF( mem );

        printf( "testing vips_sink_file()\n" );
        vips_image_write_to_file( image, "x.v", NULL );

        VIPS_UNREF( image );
        
        return( 0 );
}       

Sometimes won't print 100%:

$ ./a.out 
testing vips_sink()
posteval_cb: percent = 99
sum = 5040000
testing vips_sink_memory()
posteval_cb: percent = 99
testing vips_sink_file()
posteval_cb: percent = 99
$ ./a.out 
testing vips_sink()
posteval_cb: percent = 100
sum = 5040000
testing vips_sink_memory()
posteval_cb: percent = 99
testing vips_sink_file()
posteval_cb: percent = 100

Seems to affect all sinks, seems to only affect progress reporting (not the result of processing).

[jcupitt]

After some digging, this is just because signal emission can be delayed under load. Fix by just locking progress to 100% before triggering posteval.