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# A Parallel Mandelbrot Set Plotter
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This program plots the Mandelbrot set and writes it out as a PNG file. It uses Rust's concurrency primitives to distribute the work across eight threads.
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Different commits show different implementation strategies:
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* [Branch `single-threaded`](https://github.com/jorendorff/rust-mandelbrot/blob/single-threaded/src/main.rs)
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is the base version of the program. It does all the work on the main
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thread.
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* [Branch `bands`](https://github.com/jorendorff/rust-mandelbrot/commit/bands)
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splits the plotting area up into eight bands, and assigns one thread
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to each. This often makes poor use of the threads, because some
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bands take significantly longer than others to complete: once a fast
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thread completes its band, its CPU goes idle while its less
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fortunate brethren are still hard at work.
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* [Branch `task-queue`](https://github.com/jorendorff/rust-mandelbrot/commit/task-queue)
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gets an almost perfect linear speedup from its threads. It splits
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the plotting area up into many more bands, and then has threads draw
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bands from a common pool until the pool is empty. When a thread
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finishes one band, it goes back for more work. Since the bands still
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take different amounts of time to render, the problem cited above
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still occurs, but on a much smaller scale.
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* [Branch `lockfree`](https://github.com/jorendorff/rust-mandelbrot/commit/lockfree)
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uses Rust's atomic types to implement a lock-free iterator type, and
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uses that to dole out bands from the pool instead of a
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mutex-protected count. On Linux, this is no faster than the
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mutex-based version, which isn't too surprising: on Linux, locking
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and unlocking an uncontended mutex *is* simply a pair of atomic
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operations.
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* [Branch `rayon`](https://github.com/jorendorff/rust-mandelbrot/commit/rayon)
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uses the Rayon library instead of Crossbeam. Rayon provides a
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*parallel iterator* API that makes our code much simpler. It looks
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a lot like Rust code that uses plain old iterators.
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