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105 lines
3.5 KiB
Python
105 lines
3.5 KiB
Python
import _winapi
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import msvcrt
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import os
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import subprocess
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import uuid
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from test import support
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# Max size of asynchronous reads
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BUFSIZE = 8192
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# Exponential damping factor (see below)
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LOAD_FACTOR_1 = 0.9200444146293232478931553241
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# Seconds per measurement
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SAMPLING_INTERVAL = 5
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COUNTER_NAME = r'\System\Processor Queue Length'
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class WindowsLoadTracker():
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"""
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This class asynchronously interacts with the `typeperf` command to read
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the system load on Windows. Mulitprocessing and threads can't be used
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here because they interfere with the test suite's cases for those
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modules.
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"""
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def __init__(self):
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self.load = 0.0
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self.start()
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def start(self):
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# Create a named pipe which allows for asynchronous IO in Windows
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pipe_name = r'\\.\pipe\typeperf_output_' + str(uuid.uuid4())
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open_mode = _winapi.PIPE_ACCESS_INBOUND
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open_mode |= _winapi.FILE_FLAG_FIRST_PIPE_INSTANCE
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open_mode |= _winapi.FILE_FLAG_OVERLAPPED
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# This is the read end of the pipe, where we will be grabbing output
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self.pipe = _winapi.CreateNamedPipe(
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pipe_name, open_mode, _winapi.PIPE_WAIT,
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1, BUFSIZE, BUFSIZE, _winapi.NMPWAIT_WAIT_FOREVER, _winapi.NULL
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)
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# The write end of the pipe which is passed to the created process
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pipe_write_end = _winapi.CreateFile(
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pipe_name, _winapi.GENERIC_WRITE, 0, _winapi.NULL,
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_winapi.OPEN_EXISTING, 0, _winapi.NULL
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)
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# Open up the handle as a python file object so we can pass it to
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# subprocess
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command_stdout = msvcrt.open_osfhandle(pipe_write_end, 0)
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# Connect to the read end of the pipe in overlap/async mode
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overlap = _winapi.ConnectNamedPipe(self.pipe, overlapped=True)
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overlap.GetOverlappedResult(True)
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# Spawn off the load monitor
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command = ['typeperf', COUNTER_NAME, '-si', str(SAMPLING_INTERVAL)]
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self.p = subprocess.Popen(command, stdout=command_stdout, cwd=support.SAVEDCWD)
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# Close our copy of the write end of the pipe
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os.close(command_stdout)
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def close(self):
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if self.p is None:
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return
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self.p.kill()
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self.p.wait()
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self.p = None
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def __del__(self):
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self.close()
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def read_output(self):
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import _winapi
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overlapped, _ = _winapi.ReadFile(self.pipe, BUFSIZE, True)
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bytes_read, res = overlapped.GetOverlappedResult(False)
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if res != 0:
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return
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return overlapped.getbuffer().decode()
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def getloadavg(self):
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typeperf_output = self.read_output()
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# Nothing to update, just return the current load
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if not typeperf_output:
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return self.load
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# Process the backlog of load values
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for line in typeperf_output.splitlines():
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# typeperf outputs in a CSV format like this:
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# "07/19/2018 01:32:26.605","3.000000"
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toks = line.split(',')
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# Ignore blank lines and the initial header
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if line.strip() == '' or (COUNTER_NAME in line) or len(toks) != 2:
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continue
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load = float(toks[1].replace('"', ''))
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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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new_load = self.load * LOAD_FACTOR_1 + load * (1.0 - LOAD_FACTOR_1)
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self.load = new_load
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return self.load
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