From d64c12f9240be07f8fa33bef288d0c9a64bc8186 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Micha=C5=82=20Rudowicz?= <michal.rudowicz@fl9.eu>
Date: Sat, 28 Nov 2020 21:43:02 +0100
Subject: [PATCH] map_parallel

---
 spec/gmi_renderer_spec.cr |  1 +
 spec/map_parallel_spec.cr | 21 +++++++++++++++++++++
 spec/spec_helper.cr       |  1 -
 src/main.cr               | 26 ++++++++++----------------
 src/map_parallel.cr       | 15 +++++++++++++++
 5 files changed, 47 insertions(+), 17 deletions(-)
 create mode 100644 spec/map_parallel_spec.cr
 create mode 100644 src/map_parallel.cr

diff --git a/spec/gmi_renderer_spec.cr b/spec/gmi_renderer_spec.cr
index 4632f3e..95a2e91 100644
--- a/spec/gmi_renderer_spec.cr
+++ b/spec/gmi_renderer_spec.cr
@@ -1,4 +1,5 @@
 require "./spec_helper"
+require "../src/gmi_renderer.cr"
 
 def render_to_gmi(input : String)
   GmiRenderer.new.render(Markd::Parser.parse(input))
diff --git a/spec/map_parallel_spec.cr b/spec/map_parallel_spec.cr
new file mode 100644
index 0000000..f8ba039
--- /dev/null
+++ b/spec/map_parallel_spec.cr
@@ -0,0 +1,21 @@
+require "benchmark"
+
+require "./spec_helper"
+require "../src/map_parallel"
+
+describe "MapParallel" do
+  it "has the same output effect as simple map" do
+    input = (0..5000)
+
+    input.map_parallel { |x| x + 1 }.should eq(input.map { |x| x + 1 })
+  end
+
+  it "should be faster than running all blocks serially" do
+    ts = Time::Span.new(nanoseconds: 10_000)
+    executions = 5000
+    input = (0..executions)
+
+    Benchmark.realtime { input.map_parallel { |x| sleep(ts) } }
+      .should be < (ts*executions*0.5)
+  end
+end
diff --git a/spec/spec_helper.cr b/spec/spec_helper.cr
index 4593745..e2f4f80 100644
--- a/spec/spec_helper.cr
+++ b/spec/spec_helper.cr
@@ -1,2 +1 @@
 require "spec"
-require "../src/gmi_renderer.cr"
diff --git a/src/main.cr b/src/main.cr
index 86efe9d..f948541 100644
--- a/src/main.cr
+++ b/src/main.cr
@@ -1,24 +1,18 @@
 require "markd"
 require "./gmi_renderer"
-
-wait = Channel(Nil).new
-
-files_to_process = 0
+require "./map_parallel"
 
 Dir.new(".").entries
   .select! { |x| /\.md$/ =~ x }
   .tap { |x| files_to_process = x.size }
-  .each do |fname|
-    spawn do
-      rendered = GmiRenderer.new.render(
-        Markd::Parser.parse(
-          File.read(fname)
-        )
+  .map_parallel do |fname|
+    {fname, GmiRenderer.new.render(
+      Markd::Parser.parse(
+        File.read(fname)
       )
-      puts "======= #{fname} =======\n"
-      puts "#{rendered}\n"
-      wait.send(nil)
-    end
+    )}
+  end
+  .each do |fname, rendered|
+    puts "======= #{fname} =======\n"
+    puts "#{rendered}\n"
   end
-
-files_to_process.times { wait.receive }
diff --git a/src/map_parallel.cr b/src/map_parallel.cr
new file mode 100644
index 0000000..655aba7
--- /dev/null
+++ b/src/map_parallel.cr
@@ -0,0 +1,15 @@
+module Enumerable(T)
+  def map_parallel(&block : T -> U) forall U
+    wait = Channel(U).new
+    num_fibers = 0
+    self
+      .tap { |x| num_fibers = x.size }
+      .each do |x|
+        spawn do
+          wait.send(block.call(x))
+        end
+      end
+    Array.new(num_fibers, nil)
+      .map { |x| wait.receive }
+  end
+end
-- 
2.45.2