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.

The book shows several different versions of this program: single- and multi-threaded versions in the "Tour of Rust" chapter, and a final version based on the Rayon crate in the "Concurrency" chapter, which makes more effective use of parallelism.

Each of these versions appears on a different branch in this repository:

• Branch single-threaded is the base version of the program. It does all the work on the main thread. This is the first version shown in the "Tour of Rust" chapter.

• Branch 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. This is the final version shown in the Tour.

• Branch 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. This version is not shown in the book.

• Branch 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. This version is also not shown in the book.

• Branch 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. This is the final version shown in the Concurrency chapter.

License

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