8000 Switch to per-file locking. · matplotlib/matplotlib@5a47356 · GitHub
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anntzeranntzer
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Switch to per-file locking.
Replace the Locked contextmanager (which locks a directory, preventing other (cooperative) processes to access it) by a private _lock_path contextmanager, which locks a single file (or directory). - The finer grained lock avoids locking out the entire tex cache when handling usetex, which is useful when running multiple processes at once. - Python3 implements the `"x"` ("exclusive") mode to open, which we can use instead of relying on `makedirs` to achieve a race-free operation on the filesystem. - The previous implementation allowed multiple threads of a single process to acquire the same lock, but (for the use cases here, e.g. running a tex subprocess) this is actually undesirable. Removing this behavior also simplifies the implementation. - As far as I can tell, the previous implementation was actually racy: in retries = 50 sleeptime = 0.1 while retries: files = glob.glob(self.pattern) if files and not files[0].endswith(self.end): time.sleep(sleeptime) retries -= 1 else: break else: err_str = _lockstr.format(self.pattern) raise self.TimeoutError(err_str) # <----- HERE if not files: try: os.makedirs(self.lock_path) except OSError: pass else: # PID lock already here --- someone else will remove it. self.remove = False multiple processes can reach "HERE" at the same time and each successfully create their own lock.
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-6
lines changed

4 files changed

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‎doc/api/next_api_changes/2018-02-15-AL-deprecations.rst‎

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@@ -4,5 +4,6 @@ The following functions and classes are deprecated:
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- ``cbook.GetRealpathAndStat`` (which is only a helper for
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``get_realpath_and_stat``),
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- ``cbook.Locked``,
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- ``cbook.is_numlike`` (use ``isinstance(..., numbers.Number)`` instead),
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- ``mathtext.unichr_safe`` (use ``chr`` instead),

‎lib/matplotlib/cbook/__init__.py‎

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@@ -24,6 +24,7 @@
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import numbers
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import operator
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import os
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from pathlib import Path
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import re
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import sys
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import time
@@ -2488,6 +2489,7 @@ def get_label(y, default_name):
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"""
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@deprecated("3.0")
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class Locked(object):
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"""
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Context manager to handle locks.
@@ -2543,6 +2545,43 @@ def __exit__(self, exc_type, exc_value, traceback):
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pass
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@contextlib.contextmanager
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def _lock_path(path):
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"""
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Context manager for locking a path.
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Usage::
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with _lock_path(path):
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...
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Another thread or process that attempts to lock the same path will wait
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until this context manager is exited.
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The lock is implemented by creating a temporary file in the parent
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directory, so that directory must exist and be writable.
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"""
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path = Path(path)
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lock_path = path.with_name(path.name + ".matplotlib-lock")
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retries = 50
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sleeptime = 0.1
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for _ in range(retries):
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try:
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with lock_path.open("xb"):
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pass
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except FileExistsError:
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time.sleep(sleeptime)
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continue
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else:
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break
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else:
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raise TimeoutError(_lockstr.format(lock_path))
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try:
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yield
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finally:
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lock_path.unlink()
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def _topmost_artist(
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artists,
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_cached_max=functools.partial(max, key=operator.attrgetter("zorder"))):

‎lib/matplotlib/font_manager.py‎

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@@ -1446,7 +1446,7 @@ def _rebuild():
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fontManager = FontManager()
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if _fmcache:
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with cbook.Locked(cachedir):
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with cbook._lock_path(_fmcache):
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json_dump(fontManager, _fmcache)
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_log.info("generated new fontManager")
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@@ -1459,9 +1459,9 @@ def _rebuild():
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else:
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fontManager.default_size = None
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_log.debug("Using fontManager instance from %s", _fmcache)
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except cbook.Locked.TimeoutError:
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except TimeoutError:
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raise
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except:
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except Exception:
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_rebuild()
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else:
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_rebuild()

‎lib/matplotlib/texmanager.py‎

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@@ -50,9 +50,8 @@
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import distutils.version
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import numpy as np
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import matplotlib as mpl
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from matplotlib import rcParams
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from matplotlib import cbook, rcParams
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from matplotlib._png import read_png
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from matplotlib.cbook import Locked
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from matplotlib.compat.subprocess import subprocess, Popen, PIPE, STDOUT
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import matplotlib.dviread as dviread
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import re
@@ -360,7 +359,7 @@ def make_dvi(self, tex, fontsize):
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dvifile = '%s.dvi' % basefile
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if not os.path.exists(dvifile):
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texfile = self.make_tex(tex, fontsize)
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with Locked(self.texcache):
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with cbook._lock_path(texfile):
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self._run_checked_subprocess(
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["latex", "-interaction=nonstopmode", "--halt-on-error",
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texfile], tex)

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