Viewing file:  win_utils.py (4.45 KB) -rw-r--r--
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import _overlapped
import _thread
import _winapi
import math
import struct
import winreg
# 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
class WindowsLoadTracker():
"""
This class asynchronously reads the performance counters to calculate
the system load on Windows. A "raw" thread is used here to prevent
interference with the test suite's cases for the threading module.
"""
def __init__(self):
# Pre-flight test for access to the performance data;
# `PermissionError` will be raised if not allowed
winreg.QueryInfoKey(winreg.HKEY_PERFORMANCE_DATA)
self._values = []
self._load = None
self._running = _overlapped.CreateEvent(None, True, False, None)
self._stopped = _overlapped.CreateEvent(None, True, False, None)
_thread.start_new_thread(self._update_load, (), {})
def _update_load(self,
# localize module access to prevent shutdown errors
_wait=_winapi.WaitForSingleObject,
_signal=_overlapped.SetEvent):
# run until signaled to stop
while _wait(self._running, 1000):
self._calculate_load()
# notify stopped
_signal(self._stopped)
def _calculate_load(self,
# localize module access to prevent shutdown errors
_query=winreg.QueryValueEx,
_hkey=winreg.HKEY_PERFORMANCE_DATA,
_unpack=struct.unpack_from):
# get the 'System' object
data, _ = _query(_hkey, '2')
# PERF_DATA_BLOCK {
# WCHAR Signature[4] 8 +
# DWOWD LittleEndian 4 +
# DWORD Version 4 +
# DWORD Revision 4 +
# DWORD TotalByteLength 4 +
# DWORD HeaderLength = 24 byte offset
# ...
# }
obj_start, = _unpack('L', data, 24)
# PERF_OBJECT_TYPE {
# DWORD TotalByteLength
# DWORD DefinitionLength
# DWORD HeaderLength
# ...
# }
data_start, defn_start = _unpack('4xLL', data, obj_start)
data_base = obj_start + data_start
defn_base = obj_start + defn_start
# find the 'Processor Queue Length' counter (index=44)
while defn_base < data_base:
# PERF_COUNTER_DEFINITION {
# DWORD ByteLength
# DWORD CounterNameTitleIndex
# ... [7 DWORDs/28 bytes]
# DWORD CounterOffset
# }
size, idx, offset = _unpack('LL28xL', data, defn_base)
defn_base += size
if idx == 44:
counter_offset = data_base + offset
# the counter is known to be PERF_COUNTER_RAWCOUNT (DWORD)
processor_queue_length, = _unpack('L', data, counter_offset)
break
else:
return
# 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
# 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)
def close(self, kill=True):
self.__del__()
return
def __del__(self,
# localize module access to prevent shutdown errors
_wait=_winapi.WaitForSingleObject,
_close=_winapi.CloseHandle,
_signal=_overlapped.SetEvent):
if self._running is not None:
# tell the update thread to quit
_signal(self._running)
# wait for the update thread to signal done
_wait(self._stopped, -1)
# cleanup events
_close(self._running)
_close(self._stopped)
self._running = self._stopped = None
def getloadavg(self):
return self._load
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