lib: intro performance_analysis

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>

diff --git a/lib/performance_analysis.nit b/lib/performance_analysis.nit
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+# This file is part of NIT (http://www.nitlanguage.org).
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#       http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# Services to gather information on the performance of events by categories
+#
+# Provides `PerfMap` to manage all the categories and
+# `PerfEntry` for per-category statistics.
+#
+# ~~~
+# for i in 100.times do
+#     var clock = new Clock
+#
+#     # Do some "work" here
+#     nanosleep(0, 1000000)
+#
+#     # Register the perf
+#     sys.perfs["sleep 1ms"].add clock.lapse
+#
+#     # Do some other "work" here
+#     nanosleep(0, 5000000)
+#
+#     # Register the perf
+#     sys.perfs["sleep 5ms"].add clock.lapse
+# end
+#
+# assert sys.perfs["sleep 1ms"].count == 100
+# assert sys.perfs["sleep 1ms"].avg.is_approx(0.001, 0.0001)
+# assert sys.perfs["sleep 5ms"].avg.is_approx(0.005, 0.0005)
+# ~~~
+module performance_analysis
+
+import realtime
+
+redef class Sys
+       # Main `PerfMap` available by default
+       var perfs = new PerfMap
+end
+
+# Collection of statistics on many events
+class PerfMap
+       super HashMap[String, PerfEntry]
+
+       redef fun provide_default_value(key)
+       do
+               if not key isa String then return super
+
+               var ts = new PerfEntry(key)
+               self[key] = ts
+               return ts
+       end
+
+       redef fun to_s do return "* " + join(": ", "\n* ")
+end
+
+# Statistics on wall clock execution time of a category of events by `name`
+class PerfEntry
+
+       # Name of the category
+       var name: String
+
+       # Shortest execution time of registered events
+       var min = 0.0
+
+       # Longest execution time of registered events
+       var max = 0.0
+
+       # Average execution time of registered events
+       var avg = 0.0
+
+       # Number of registered events
+       var count = 0
+
+       # Register a new event execution time with a `Timespec`
+       fun add(lapse: Timespec) do add_float lapse.to_f
+
+       # Register a new event execution time in seconds using a `Float`
+       fun add_float(time: Float)
+       do
+               if time.to_f < min.to_f or count == 0 then min = time
+               if time.to_f > max.to_f then max = time
+
+               avg = (avg * count.to_f + time) / (count+1).to_f
+               count += 1
+       end
+
+       redef fun to_s do return "min {min}, max {max}, avg {avg}, count {count}"
+end