# A Parallel Mandelbrot Set Plotter

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.

Different commits show different implementation strategies:

*   [Branch `single-threaded`](https://github.com/ProgrammingRust/mandelbrot/tree/single-threaded)
    is the base version of the program. It does all the work on the main
    thread.

*   [Branch `bands`](https://github.com/ProgrammingRust/mandelbrot/tree/bands)
    splits the plotting area up into eight bands, and assigns one thread
    to each.  This often makes poor use of the threads, because some
    bands take significantly longer than others to complete: once a fast
    thread completes its band, its CPU goes idle while its less
    fortunate brethren are still hard at work.

*   [Branch `task-queue`](https://github.com/ProgrammingRust/mandelbrot/tree/task-queue)
    gets an almost perfect linear speedup from its threads. It splits
    the plotting area up into many more bands, and then has threads draw
    bands from a common pool until the pool is empty. When a thread
    finishes one band, it goes back for more work. Since the bands still
    take different amounts of time to render, the problem cited above
    still occurs, but on a much smaller scale.

*   [Branch `lockfree`](https://github.com/ProgrammingRust/mandelbrot/tree/lockfree)
    uses Rust's atomic types to implement a lock-free iterator type, and
    uses that to dole out bands from the pool instead of a
    mutex-protected count. On Linux, this is no faster than the
    mutex-based version, which isn't too surprising: on Linux, locking
    and unlocking an uncontended mutex *is* simply a pair of atomic
    operations.

*   [Branch `rayon`](https://github.com/ProgrammingRust/mandelbrot/tree/rayon)
    uses the Rayon library instead of Crossbeam. Rayon provides a
    *parallel iterator* API that makes our code much simpler.  It looks
    a lot like Rust code that uses plain old iterators.

## License

The example code in this directory and its subdirectories is licensed under the
terms of the MIT license. See [LICENSE-MIT](LICENSE-MIT) for details.