Use flock() for file locking

.gitignore

@@ -14,3 +14,4 @@ nbproject
 .DS_Store
 /*egg-info
 /.tox
+.cache

AUTHORS

@@ -15,5 +15,6 @@ Contributors are:
 -Jonathan Chu <jonathan.chu _at_ me.com>
 -Vincent Driessen <me _at_ nvie.com>
 -Phil Elson <pelson _dot_ pub _at_ gmail.com>
+-Daniele Esposti <daniele.esposti _at_ gmail.com>
 
 Portions derived from other open source works and are clearly marked.

git/test/test_util.py

@@ -5,6 +5,7 @@
 # the BSD License: http://www.opensource.org/licenses/bsd-license.php
 
 import tempfile
+import gc
 
 from git.test.lib import (
     TestBase,
@@ -80,6 +81,7 @@ def test_lock_file(self):
 
         # auto-release on destruction
         del(other_lock_file)
+        gc.collect()
         lock_file._obtain_lock_or_raise()
         lock_file._release_lock()
 

git/util.py

@@ -48,6 +48,56 @@
 
 #{ Utility Methods
 
+if platform.system() == 'Windows':
+    # This code is a derivative work of Portalocker http://code.activestate.com/recipes/65203/
+    import win32con
+    import win32file
+    import pywintypes
+
+    LOCK_EX = win32con.LOCKFILE_EXCLUSIVE_LOCK
+    LOCK_SH = 0  # the default
+    LOCK_NB = win32con.LOCKFILE_FAIL_IMMEDIATELY
+    LOCK_UN = 1 << 2
+
+    __overlapped = pywintypes.OVERLAPPED()
+
+    def flock(fd, flags=0):
+        hfile = win32file._get_osfhandle(fd)
+
+        if flags & LOCK_UN != 0:
+            # Unlock file descriptor
+            try:
+                win32file.UnlockFileEx(hfile, 0, -0x10000, __overlapped)
+            except pywintypes.error as exc_value:
+                # error: (158, 'UnlockFileEx', 'The segment is already unlocked.')
+                # To match the 'posix' implementation, silently ignore this error
+                if exc_value[0] == 158:
+                    pass
+                else:
+                    # Q:  Are there exceptions/codes we should be dealing with here?
+                    raise
+
+        elif flags & LOCK_EX != 0:
+            # Lock file
+            try:
+                win32file.LockFileEx(hfile, flags, 0, -0x10000, __overlapped)
+            except pywintypes.error as exc_value:
+                if exc_value[0] == 33:
+                    # error: (33, 'LockFileEx',
+                    # 'The process cannot access the file because another process has locked
+                    # a portion of the file.')
+                    raise IOError(33, exc_value[2])
+                else:
+                    # Q:  Are there exceptions/codes we should be dealing with here?
+                    raise
+
+        else:
+            raise NotImplementedError("Unsupported set of bitflags {}".format(bin(flags)))
+
+
+else:
+    from fcntl import flock, LOCK_UN, LOCK_EX, LOCK_NB
+
 
 def unbare_repo(func):
     """Methods with this decorator raise InvalidGitRepositoryError if they
@@ -555,9 +605,10 @@ class LockFile(object):
     As we are a utility class to be derived from, we only use protected methods.
 
     Locks will automatically be released on destruction"""
-    __slots__ = ("_file_path", "_owns_lock")
+    __slots__ = ("_file_path", "_owns_lock", "_file_descriptor")
 
     def __init__(self, file_path):
+        self._file_descriptor = None
         self._file_path = file_path
         self._owns_lock = False
 
@@ -579,20 +630,21 @@ def _obtain_lock_or_raise(self):
         :raise IOError: if a lock was already present or a lock file could not be written"""
         if self._has_lock():
             return
+
         lock_file = self._lock_file_path()
-        if os.path.isfile(lock_file):
-            raise IOError("Lock for file %r did already exist, delete %r in case the lock is illegal" %
-                          (self._file_path, lock_file))
 
+        # Create file and lock
         try:
-            flags = os.O_WRONLY | os.O_CREAT | os.O_EXCL
+            flags = os.O_CREAT
             if is_win:
                 flags |= os.O_SHORT_LIVED
             fd = os.open(lock_file, flags, 0)
-            os.close(fd)
         except OSError as e:
             raise IOError(str(e))
 
+        flock(fd, LOCK_EX | LOCK_NB)
+
+        self._file_descriptor = fd
         self._owns_lock = True
 
     def _obtain_lock(self):
@@ -605,14 +657,21 @@ def _release_lock(self):
         if not self._has_lock():
             return
 
+        fd = self._file_descriptor
+        lock_file = self._lock_file_path()
+
+        flock(fd, LOCK_UN)
+        os.close(fd)
+
         # if someone removed our file beforhand, lets just flag this issue
         # instead of failing, to make it more usable.
-        lfp = self._lock_file_path()
         try:
-            rmfile(lfp)
+            rmfile(lock_file)
         except OSError:
             pass
+
         self._owns_lock = False
+        self._file_descriptor = None
 
 
 class BlockingLockFile(LockFile):
@@ -647,7 +706,7 @@ def _obtain_lock(self):
             try:
                 super(BlockingLockFile, self)._obtain_lock()
             except IOError:
-                # synity check: if the directory leading to the lockfile is not
+                # sanity check: if the directory leading to the lockfile is not
                 # readable anymore, raise an execption
                 curtime = time.time()
                 if not os.path.isdir(os.path.dirname(self._lock_file_path())):

setup.py

@@ -13,6 +13,7 @@
 import logging
 import os
 import sys
+import platform
 from os import path
 
 with open(path.join(path.dirname(__file__), 'VERSION')) as v:
@@ -21,6 +22,10 @@
 with open('requirements.txt') as reqs_file:
     requirements = reqs_file.read().splitlines()
 
+if platform.system() == 'Windows':
+    with open('win32-requirements.txt') as reqs_file:
+        requirements += reqs_file.read().splitlines()
+
 
 class build_py(_build_py):
 
@@ -65,6 +70,8 @@ def _stamp_version(filename):
         print("WARNING: Couldn't find version line in file %s" % filename, file=sys.stderr)
 
 install_requires = ['gitdb >= 0.6.4']
+if platform.system() == 'Windows':
+    install_requires.append("pypiwin32 >= 219")
 extras_require = {
     ':python_version == "2.6"': ['ordereddict'],
 }

win32-requirements.txt

@@ -0,0 +1,2 @@
+-r requirements.txt
+pypiwin32 >= 219