diff options
Diffstat (limited to 'monotonic.py')
| -rw-r--r-- | monotonic.py | 164 |
1 files changed, 164 insertions, 0 deletions
diff --git a/monotonic.py b/monotonic.py new file mode 100644 index 0000000..a3552c0 --- /dev/null +++ b/monotonic.py @@ -0,0 +1,164 @@ +# -*- coding: utf-8 -*- +""" + monotonic + ~~~~~~~~~ + + This module provides a ``monotonic()`` function which returns the + value (in fractional seconds) of a clock which never goes backwards. + + On Python 3.3 or newer, ``monotonic`` will be an alias of + ``time.monotonic`` from the standard library. On older versions, + it will fall back to an equivalent implementation: + + +-------------+--------------------+ + | Linux, BSD | clock_gettime(3) | + +-------------+--------------------+ + | Windows | GetTickCount[64] | + +-------------+--------------------+ + | OS X | mach_absolute_time | + +-------------+--------------------+ + + If no suitable implementation exists for the current platform, + attempting to import this module (or to import from it) will + cause a RuntimeError exception to be raised. + + + Copyright 2014 Ori Livneh <ori@wikimedia.org> + + Licensed under the Apache License, Version 2.0 (the "License"); + you may not use this file except in compliance with the License. + You may obtain a copy of the License at + + http://www.apache.org/licenses/LICENSE-2.0 + + Unless required by applicable law or agreed to in writing, software + distributed under the License is distributed on an "AS IS" BASIS, + WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + See the License for the specific language governing permissions and + limitations under the License. + +""" +import ctypes +import ctypes.util +import os +import sys +import time +import threading + + +__all__ = ('monotonic',) + + +try: + monotonic = time.monotonic +except AttributeError: + try: + if sys.platform == 'darwin': # OS X, iOS + # See Technical Q&A QA1398 of the Mac Developer Library: + # <https://developer.apple.com/library/mac/qa/qa1398/> + libc = ctypes.CDLL('/usr/lib/libc.dylib', use_errno=True) + + class mach_timebase_info_data_t(ctypes.Structure): + """System timebase info. Defined in <mach/mach_time.h>.""" + _fields_ = (('numer', ctypes.c_uint32), + ('denom', ctypes.c_uint32)) + + mach_absolute_time = libc.mach_absolute_time + mach_absolute_time.restype = ctypes.c_uint64 + + timebase = mach_timebase_info_data_t() + libc.mach_timebase_info(ctypes.byref(timebase)) + ticks_per_second = timebase.numer / timebase.denom * 1.0e9 + + def monotonic(): + """Monotonic clock, cannot go backward.""" + return mach_absolute_time() / ticks_per_second + + elif sys.platform.startswith('win32') or sys.platform.startswith('cygwin'): + if sys.platform.startswith('cygwin'): + # Note: cygwin implements clock_gettime (CLOCK_MONOTONIC = 4) since + # version 1.7.6. Using raw WinAPI for maximum version compatibility. + + # Ugly hack using the wrong calling convention (in 32-bit mode) + # because ctypes has no windll under cygwin (and it also seems that + # the code letting you select stdcall in _ctypes doesn't exist under + # the preprocessor definitions relevant to cygwin). + # This is 'safe' because: + # 1. The ABI of GetTickCount and GetTickCount64 is identical for + # both calling conventions because they both have no parameters. + # 2. libffi masks the problem because after making the call it doesn't + # touch anything through esp and epilogue code restores a correct + # esp from ebp afterwards. + kernel32 = ctypes.cdll.kernel32 + else: + kernel32 = ctypes.windll.kernel32 + + GetTickCount64 = getattr(kernel32, 'GetTickCount64', None) + if GetTickCount64: + # Windows Vista / Windows Server 2008 or newer. + GetTickCount64.restype = ctypes.c_ulonglong + + def monotonic(): + """Monotonic clock, cannot go backward.""" + return GetTickCount64() / 1000.0 + + else: + # Before Windows Vista. + GetTickCount = kernel32.GetTickCount + GetTickCount.restype = ctypes.c_uint32 + + get_tick_count_lock = threading.Lock() + get_tick_count_last_sample = 0 + get_tick_count_wraparounds = 0 + + def monotonic(): + """Monotonic clock, cannot go backward.""" + global get_tick_count_last_sample + global get_tick_count_wraparounds + + with get_tick_count_lock: + current_sample = GetTickCount() + if current_sample < get_tick_count_last_sample: + get_tick_count_wraparounds += 1 + get_tick_count_last_sample = current_sample + + final_milliseconds = get_tick_count_wraparounds << 32 + final_milliseconds += get_tick_count_last_sample + return final_milliseconds / 1000.0 + + else: + try: + clock_gettime = ctypes.CDLL(ctypes.util.find_library('c'), + use_errno=True).clock_gettime + except AttributeError: + clock_gettime = ctypes.CDLL(ctypes.util.find_library('rt'), + use_errno=True).clock_gettime + + class timespec(ctypes.Structure): + """Time specification, as described in clock_gettime(3).""" + _fields_ = (('tv_sec', ctypes.c_long), + ('tv_nsec', ctypes.c_long)) + + if sys.platform.startswith('linux'): + CLOCK_MONOTONIC = 1 + elif sys.platform.startswith('freebsd'): + CLOCK_MONOTONIC = 4 + elif sys.platform.startswith('sunos5'): + CLOCK_MONOTONIC = 4 + elif 'bsd' in sys.platform: + CLOCK_MONOTONIC = 3 + + def monotonic(): + """Monotonic clock, cannot go backward.""" + ts = timespec() + if clock_gettime(CLOCK_MONOTONIC, ctypes.pointer(ts)): + errno = ctypes.get_errno() + raise OSError(errno, os.strerror(errno)) + return ts.tv_sec + ts.tv_nsec / 1.0e9 + + # Perform a sanity-check. + if monotonic() - monotonic() > 0: + raise ValueError('monotonic() is not monotonic!') + + except Exception: + raise RuntimeError('no suitable implementation for this system') |