threadweaver/examples/ThumbNailer.in.md

0001 ## Working title: Everything in moderation (and decorated)
0002
0003 Let's put the features that have been described so far and a few more
0004 that as of yet haven't been mentioned, and create a comprehensive
0005 example program. The example program calculates thumbnails for
0006 images. It will take a number of image files and, in separate steps
0007 implemented as individual jobs, load them from disk, convert them from
0008 raw data to QImages, scale the images to thumbnails, and finally save
0009 them to disk. This problem may not be most imaginative use of concurrent
0010 programming techniques, but it does demonstrate a number of practical
0011 problems. For example, the operations for each single image contain
0012 elements that are file system I/O bound and elements that are CPU
0013 bound. For large numbers of images, it has to deal with a trade-off of
0014 memory usage and CPU utlilization. Less obvious, there are also
0015 expectations on the order of execution of the jobs, so that the
0016 interface provides the user with visible feedback of the progress of
0017 the operations. An application of this kind also should provide
0018 features of load management and reduce it's own generated system load
0019 if the system is "stressed" by other processes. A web server
0020 implementation or a video coding program will have to solve similar
0021 issues to provide optimal throughput without overloading the system.
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