Add flat benchmark

Author: pitr-ch

examples/benchmark_new_futures.rb

@@ -2,11 +2,37 @@
 require 'concurrent'
 require 'concurrent-edge'
 
+# require 'ruby-prof'
+#
+# result = RubyProf.profile do
+#   1000.times do
+#     head    = Concurrent.future { 1 }
+#     branch1 = head.then(&:succ)
+#     branch2 = head.then(&:succ).then(&:succ)
+#     branch3 = head.then(&:succ).then(&:succ).then(&:succ)
+#     Concurrent.join(branch1, branch2, branch3).then { |(a, b, c)| a + b + c }.value!
+#   end
+# end
+#
+# printer = RubyProf::FlatPrinter.new(result)
+# printer.print(STDOUT)
+#
+# printer = RubyProf::GraphPrinter.new(result)
+# printer.print(STDOUT, {})
+#
+# exit
+
 scale  = 1
 time   = 10 * scale
 warmup = 2 * scale
 warmup *= 10 if Concurrent.on_jruby?
 
+Benchmark.ips(time, warmup) do |x|
+  x.report('flat-old') { Concurrent::Promise.execute { 1 }.flat_map { |v| Concurrent::Promise.execute { v + 2 } }.value! }
+  x.report('flat-new') { Concurrent.future(:fast) { 1 }.then { |v| Concurrent.future(:fast) { v+ 1 } }.flat.value! }
+  x.compare!
+end
+
 Benchmark.ips(time, warmup) do |x|
   x.report('status-old') { f = Concurrent::Promise.execute { nil }; 100.times { f.complete? } }
   x.report('status-new') { f = Concurrent.future(:fast) { nil }; 100.times { f.completed? } }