bpo-36670: Enhance regrtest (GH-16556)

* Add log() method: add timestamp and load average prefixes
  to main messages.
* WindowsLoadTracker:

  * LOAD_FACTOR_1 is now computed using SAMPLING_INTERVAL
  * Initialize the load to the arithmetic mean of the first 5 values
    of the Processor Queue Length value (so over 5 seconds), rather
    than 0.0.
  * Handle BrokenPipeError and when typeperf exit.

* format_duration(1.5) now returns '1.5 sec', rather than
  '1 sec 500 ms'

1 files changed, 47 insertions, 19 deletions

diff --git a/Lib/test/libregrtest/win_utils.py b/Lib/test/libregrtest/win_utils.py
index 0b73a94..028c011 100644
--- a/Lib/test/libregrtest/win_utils.py
+++ b/Lib/test/libregrtest/win_utils.py
@@ -1,4 +1,5 @@
 import _winapi
+import math
 import msvcrt
 import os
 import subprocess
@@ -10,11 +11,14 @@ from test.libregrtest.utils import print_warning
 
 # Max size of asynchronous reads
 BUFSIZE = 8192
-# Exponential damping factor (see below)
-LOAD_FACTOR_1 = 0.9200444146293232478931553241
-
 # Seconds per measurement
 SAMPLING_INTERVAL = 1
+# Exponential damping factor to compute exponentially weighted moving average
+# on 1 minute (60 seconds)
+LOAD_FACTOR_1 = 1 / math.exp(SAMPLING_INTERVAL / 60)
+# Initialize the load using the arithmetic mean of the first NVALUE values
+# of the Processor Queue Length
+NVALUE = 5
 # Windows registry subkey of HKEY_LOCAL_MACHINE where the counter names
 # of typeperf are registered
 COUNTER_REGISTRY_KEY = (r"SOFTWARE\Microsoft\Windows NT\CurrentVersion"
@@ -30,10 +34,10 @@ class WindowsLoadTracker():
     """
 
     def __init__(self):
-        self.load = 0.0
-        self.counter_name = ''
+        self._values = []
+        self._load = None
         self._buffer = ''
-        self.popen = None
+        self._popen = None
         self.start()
 
     def start(self):
@@ -65,7 +69,7 @@ class WindowsLoadTracker():
         # Spawn off the load monitor
         counter_name = self._get_counter_name()
         command = ['typeperf', counter_name, '-si', str(SAMPLING_INTERVAL)]
-        self.popen = subprocess.Popen(' '.join(command), stdout=command_stdout, cwd=support.SAVEDCWD)
+        self._popen = subprocess.Popen(' '.join(command), stdout=command_stdout, cwd=support.SAVEDCWD)
 
         # Close our copy of the write end of the pipe
         os.close(command_stdout)
@@ -85,12 +89,16 @@ class WindowsLoadTracker():
         process_queue_length = counters_dict['44']
         return f'"\\{system}\\{process_queue_length}"'
 
-    def close(self):
-        if self.popen is None:
+    def close(self, kill=True):
+        if self._popen is None:
             return
-        self.popen.kill()
-        self.popen.wait()
-        self.popen = None
+
+        self._load = None
+
+        if kill:
+            self._popen.kill()
+        self._popen.wait()
+        self._popen = None
 
     def __del__(self):
         self.close()
@@ -109,7 +117,7 @@ class WindowsLoadTracker():
         value = value[1:-1]
         return float(value)
 
-    def read_lines(self):
+    def _read_lines(self):
         overlapped, _ = _winapi.ReadFile(self.pipe, BUFSIZE, True)
         bytes_read, res = overlapped.GetOverlappedResult(False)
         if res != 0:
@@ -135,7 +143,21 @@ class WindowsLoadTracker():
         return lines
 
     def getloadavg(self):
-        for line in self.read_lines():
+        if self._popen is None:
+            return None
+
+        returncode = self._popen.poll()
+        if returncode is not None:
+            self.close(kill=False)
+            return None
+
+        try:
+            lines = self._read_lines()
+        except BrokenPipeError:
+            self.close()
+            return None
+
+        for line in lines:
             line = line.rstrip()
 
             # Ignore the initial header:
@@ -148,7 +170,7 @@ class WindowsLoadTracker():
                 continue
 
             try:
-                load = self._parse_line(line)
+                processor_queue_length = self._parse_line(line)
             except ValueError:
                 print_warning("Failed to parse typeperf output: %a" % line)
                 continue
@@ -156,7 +178,13 @@ class WindowsLoadTracker():
             # We use an exponentially weighted moving average, imitating the
             # load calculation on Unix systems.
             # https://en.wikipedia.org/wiki/Load_(computing)#Unix-style_load_calculation
-            new_load = self.load * LOAD_FACTOR_1 + load * (1.0 - LOAD_FACTOR_1)
-            self.load = new_load
-
-        return self.load
+            # https://en.wikipedia.org/wiki/Moving_average#Exponential_moving_average
+            if self._load is not None:
+                self._load = (self._load * LOAD_FACTOR_1
+                              + processor_queue_length  * (1.0 - LOAD_FACTOR_1))
+            elif len(self._values) < NVALUE:
+                self._values.append(processor_queue_length)
+            else:
+                self._load = sum(self._values) / len(self._values)
+
+        return self._load