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Lib/site-packages/virtualenv/util/lock.py

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+"""holds locking functionality that works across processes"""
+from __future__ import absolute_import, unicode_literals
+
+import logging
+import os
+from contextlib import contextmanager
+from threading import Lock, RLock
+
+from filelock import FileLock, Timeout
+
+from virtualenv.util.path import Path
+
+
+class _CountedFileLock(FileLock):
+    def __init__(self, lock_file):
+        parent = os.path.dirname(lock_file)
+        if not os.path.exists(parent):
+            try:
+                os.makedirs(parent)
+            except OSError:
+                pass
+        super(_CountedFileLock, self).__init__(lock_file)
+        self.count = 0
+        self.thread_safe = RLock()
+
+    def acquire(self, timeout=None, poll_intervall=0.05):
+        with self.thread_safe:
+            if self.count == 0:
+                super(_CountedFileLock, self).acquire(timeout=timeout, poll_intervall=poll_intervall)
+            self.count += 1
+
+    def release(self, force=False):
+        with self.thread_safe:
+            if self.count == 1:
+                super(_CountedFileLock, self).release()
+            self.count = max(self.count - 1, 0)
+
+
+_lock_store = {}
+_store_lock = Lock()
+
+
+class ReentrantFileLock(object):
+    def __init__(self, folder):
+        self._lock = None
+        path = Path(folder)
+        self.path = path.resolve() if path.exists() else path
+
+    def __repr__(self):
+        return "{}({})".format(self.__class__.__name__, self.path)
+
+    def __div__(self, other):
+        return ReentrantFileLock(self.path / other)
+
+    def __truediv__(self, other):
+        return self.__div__(other)
+
+    def _create_lock(self, name=""):
+        lock_file = str(self.path / "{}.lock".format(name))
+        with _store_lock:
+            if lock_file not in _lock_store:
+                _lock_store[lock_file] = _CountedFileLock(lock_file)
+            return _lock_store[lock_file]
+
+    @staticmethod
+    def _del_lock(lock):
+        with _store_lock:
+            if lock is not None:
+                with lock.thread_safe:
+                    if lock.count == 0:
+                        _lock_store.pop(lock.lock_file, None)
+
+    def __del__(self):
+        self._del_lock(self._lock)
+
+    def __enter__(self):
+        self._lock = self._create_lock()
+        self._lock_file(self._lock)
+
+    def __exit__(self, exc_type, exc_val, exc_tb):
+        self._release(self._lock)
+
+    def _lock_file(self, lock, no_block=False):
+        # multiple processes might be trying to get a first lock... so we cannot check if this directory exist without
+        # a lock, but that lock might then become expensive, and it's not clear where that lock should live.
+        # Instead here we just ignore if we fail to create the directory.
+        try:
+            os.makedirs(str(self.path))
+        except OSError:
+            pass
+        try:
+            lock.acquire(0.0001)
+        except Timeout:
+            if no_block:
+                raise
+            logging.debug("lock file %s present, will block until released", lock.lock_file)
+            lock.release()  # release the acquire try from above
+            lock.acquire()
+
+    @staticmethod
+    def _release(lock):
+        lock.release()
+
+    @contextmanager
+    def lock_for_key(self, name, no_block=False):
+        lock = self._create_lock(name)
+        try:
+            try:
+                self._lock_file(lock, no_block)
+                yield
+            finally:
+                self._release(lock)
+        finally:
+            self._del_lock(lock)
+
+
+__all__ = (
+    "Timeout",
+    "ReentrantFileLock",
+)