![]() ![]() This only added 5 – 10 minutes of execution time in total, and still provided us with a good idea of where the problems lay. ![]() Sampling, however, takes a more or less constant amount of time each second to record stack traces for each thread. Profiling our tests this way would take hours! Sometimes – such as in image processing – small, quick methods are called many, many times, adding a great deal of time to the execution. One problem with instrumented profiling is that it adds a constant amount of extra execution time to every single method call. We test our software by running our PDF to HTML5 converter on a large number of diverse PDF files which make use of different parts of the PDF specification and flagging up any changes in the output. VisualVM’s sampler, however, takes a dump of all of the threads of execution on a fairly regular basis, and uses this to work out how roughly how much CPU time each method spends. This adds extra bytecode to your methods for recording when they’re called, and how long they take to execute each time they are. VisualVM’s profiler works by “instrumenting” all of the methods of your code. I’m just going to be talking about CPU profiling, although the approaches to memory are similar. Helpfully, Java comes with both a traditional profiler and a sampler in the form of VisualVM. A recent issue we had upon the release of Java 8 proved awkward to resolve using a traditional profiler, but Sampling proved well suited to the task. Most people will already be familiar with profiling, but you might be less aware of the different types of profilers on offer. He's also enjoyed working with SVG, Java 3D, Java FX and Swing. Sam Howard Sam is a developer at IDRsolutions who specialises in font rendering and conversion.
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