Use Rayon to render each row of pixels as a separate task, processed by Rayon's built-in thread pool.

Cargo.lock

@@ -2,9 +2,9 @@
 name = "mandelbrot"
 version = "0.2.0"
 dependencies = [
- "crossbeam 0.2.9 (registry+https://github.com/rust-lang/crates.io-index)",
  "image 0.10.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "num 0.1.34 (registry+https://github.com/rust-lang/crates.io-index)",
+ "rayon 0.4.0 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
@@ -22,11 +22,6 @@ name = "color_quant"
 version = "1.0.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 
-[[package]]
-name = "crossbeam"
-version = "0.2.9"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-
 [[package]]
 name = "deque"
 version = "0.3.1"

Cargo.toml

@@ -6,4 +6,4 @@ authors = ["Jim Blandy <jimb@red-bean.com>"]
 [dependencies]
 num = "0.1.34"
 image = "0.10.1"
-crossbeam = "0.2.9"
+rayon = "0.4.0"

src/main.rs

@@ -144,10 +144,10 @@ fn measure_elapsed_time<F: FnOnce()>(f: F) -> Duration {
 }
 
 
-extern crate crossbeam;
+extern crate rayon;
 
-use std::sync::Mutex;
 use std::io::Write;
+use rayon::prelude::*;
 
 fn main() {
     let args : Vec<String> = std::env::args().collect();
@@ -172,47 +172,25 @@ fn main() {
 
     let mut pixels = vec![0; bounds.0 * bounds.1];
 
-    for threads in [1,  2,  3,  4,  5,  6,  7,  8,
-                    9, 10, 11, 12, 13, 14, 15, 16,
-                    20, 30, 40, 50, 60, 70, 80, 90,
-                    //100, 200, 300, 400, 500, 600, 700, 800, 900, 1000
-                    ].iter() {
-        let band_rows = bounds.1 / 400;
-
-        let dt = measure_elapsed_time(|| {
-            let bands = Mutex::new(pixels.chunks_mut(band_rows * bounds.0).enumerate());
-            crossbeam::scope(|scope| {
-                for i in 0..*threads {
-                    scope.spawn(|| {
-                        let mut count = 0;
-                        loop {
-                            match {
-                                let mut guard = bands.lock().unwrap();
-                                guard.next()
-                            }
-                            {
-                                None => { return; }
-                                Some((i, band)) => {
-                                    count += 1;
-                                    let top = band_rows * i;
-                                    let height = band.len() / bounds.0;
-                                    let band_bounds = (bounds.0, height);
-                                    let band_upper_left = pixel_to_point(bounds, (0, top),
-                                                                         upper_left, lower_right);
-                                    let band_lower_right = pixel_to_point(bounds, (bounds.0, top + height),
-                                                                          upper_left, lower_right);
-                                    render(band, band_bounds, band_upper_left, band_lower_right);
-                                }
-                            }
-                        }
-                    });
-                }
+    // Scope of slicing up `pixels` into horizontal bands.
+    {
+        let bands: Vec<(usize, &mut [u8])> = pixels
+            .chunks_mut(bounds.0)
+            .enumerate()
+            .collect();
+
+        bands.into_par_iter()
+            .weight_max()
+            .for_each(|(i, band)| {
+                let top = i;
+                let band_bounds = (bounds.0, 1);
+                let band_upper_left = pixel_to_point(bounds, (0, top),
+                                                     upper_left, lower_right);
+                let band_lower_right = pixel_to_point(bounds, (bounds.0, top + 1),
+                                                      upper_left, lower_right);
+                render(band, band_bounds, band_upper_left, band_lower_right);
             });
-        });
-        println!("{:4} {:.3}",
-                 threads,
-                 dt.as_secs() as f64 + dt.subsec_nanos() as f64 * 1e-9);
     }
 
-    write_bitmap(&args[1], &pixels[..], bounds).expect("error writing PNG file");
+    write_bitmap(&args[1], &pixels, bounds).expect("error writing PNG file");
 }