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19058b9f62
Replace the child process `typeperf.exe` with a daemon thread that reads the performance counters directly. This prevents the issues that arise from inherited handles in grandchild processes (see issue37531 for discussion). We only use the load tracker when running tests in multiprocess mode. This prevents inadvertent interactions with tests expecting a single threaded environment. Displaying load is really only helpful for buildbots running in multiprocess mode anyway.
124 lines
4.4 KiB
Python
124 lines
4.4 KiB
Python
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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