125 lines
4.4 KiB
Python
125 lines
4.4 KiB
Python
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import _overlapped
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import _thread
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import _winapi
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import math
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import struct
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import winreg
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# Seconds per measurement
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SAMPLING_INTERVAL = 1
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# Exponential damping factor to compute exponentially weighted moving average
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# on 1 minute (60 seconds)
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LOAD_FACTOR_1 = 1 / math.exp(SAMPLING_INTERVAL / 60)
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# Initialize the load using the arithmetic mean of the first NVALUE values
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# of the Processor Queue Length
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NVALUE = 5
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class WindowsLoadTracker():
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"""
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This class asynchronously reads the performance counters to calculate
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the system load on Windows. A "raw" thread is used here to prevent
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interference with the test suite's cases for the threading module.
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"""
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def __init__(self):
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# Pre-flight test for access to the performance data;
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# `PermissionError` will be raised if not allowed
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winreg.QueryInfoKey(winreg.HKEY_PERFORMANCE_DATA)
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self._values = []
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self._load = None
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self._running = _overlapped.CreateEvent(None, True, False, None)
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self._stopped = _overlapped.CreateEvent(None, True, False, None)
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_thread.start_new_thread(self._update_load, (), {})
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def _update_load(self,
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# localize module access to prevent shutdown errors
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_wait=_winapi.WaitForSingleObject,
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_signal=_overlapped.SetEvent):
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# run until signaled to stop
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while _wait(self._running, 1000):
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self._calculate_load()
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# notify stopped
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_signal(self._stopped)
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def _calculate_load(self,
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# localize module access to prevent shutdown errors
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_query=winreg.QueryValueEx,
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_hkey=winreg.HKEY_PERFORMANCE_DATA,
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_unpack=struct.unpack_from):
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# get the 'System' object
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data, _ = _query(_hkey, '2')
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# PERF_DATA_BLOCK {
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# WCHAR Signature[4] 8 +
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# DWOWD LittleEndian 4 +
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# DWORD Version 4 +
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# DWORD Revision 4 +
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# DWORD TotalByteLength 4 +
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# DWORD HeaderLength = 24 byte offset
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# ...
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# }
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obj_start, = _unpack('L', data, 24)
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# PERF_OBJECT_TYPE {
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# DWORD TotalByteLength
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# DWORD DefinitionLength
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# DWORD HeaderLength
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# ...
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# }
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data_start, defn_start = _unpack('4xLL', data, obj_start)
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data_base = obj_start + data_start
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defn_base = obj_start + defn_start
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# find the 'Processor Queue Length' counter (index=44)
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while defn_base < data_base:
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# PERF_COUNTER_DEFINITION {
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# DWORD ByteLength
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# DWORD CounterNameTitleIndex
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# ... [7 DWORDs/28 bytes]
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# DWORD CounterOffset
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# }
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size, idx, offset = _unpack('LL28xL', data, defn_base)
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defn_base += size
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if idx == 44:
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counter_offset = data_base + offset
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# the counter is known to be PERF_COUNTER_RAWCOUNT (DWORD)
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processor_queue_length, = _unpack('L', data, counter_offset)
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break
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else:
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return
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# We use an exponentially weighted moving average, imitating the
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# load calculation on Unix systems.
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# https://en.wikipedia.org/wiki/Load_(computing)#Unix-style_load_calculation
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# https://en.wikipedia.org/wiki/Moving_average#Exponential_moving_average
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if self._load is not None:
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self._load = (self._load * LOAD_FACTOR_1
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+ processor_queue_length * (1.0 - LOAD_FACTOR_1))
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elif len(self._values) < NVALUE:
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self._values.append(processor_queue_length)
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else:
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self._load = sum(self._values) / len(self._values)
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def close(self, kill=True):
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self.__del__()
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return
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def __del__(self,
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# localize module access to prevent shutdown errors
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_wait=_winapi.WaitForSingleObject,
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_close=_winapi.CloseHandle,
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_signal=_overlapped.SetEvent):
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if self._running is not None:
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# tell the update thread to quit
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_signal(self._running)
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# wait for the update thread to signal done
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_wait(self._stopped, -1)
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# cleanup events
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_close(self._running)
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_close(self._stopped)
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self._running = self._stopped = None
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def getloadavg(self):
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return self._load
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