mandelbrot's Introduction

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 is the base version of the program. It does all the work on the main thread.
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.
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.
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.
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.