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  • Committer: Robert Collins
  • Date: 2005-09-28 09:35:50 UTC
  • mfrom: (1185.1.47)
  • Revision ID: robertc@robertcollins.net-20050928093550-3ca194dfaffc79f1
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bzrlib/lock.py
 
1
# Copyright (C) 2005 Canonical Ltd
 
2
 
 
3
# This program is free software; you can redistribute it and/or modify
 
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# it under the terms of the GNU General Public License as published by
 
5
# the Free Software Foundation; either version 2 of the License, or
 
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# (at your option) any later version.
 
7
 
 
8
# This program is distributed in the hope that it will be useful,
 
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
 
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 
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# GNU General Public License for more details.
 
12
 
 
13
# You should have received a copy of the GNU General Public License
 
14
# along with this program; if not, write to the Free Software
 
15
# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 
16
 
 
17
 
 
18
"""Locking wrappers.
 
19
 
 
20
This only does local locking using OS locks for now.
 
21
 
 
22
This module causes two methods, lock() and unlock() to be defined in
 
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any way that works on the current platform.
 
24
 
 
25
It is not specified whether these locks are reentrant (i.e. can be
 
26
taken repeatedly by a single process) or whether they exclude
 
27
different threads in a single process.  
 
28
 
 
29
Eventually we may need to use some kind of lock representation that
 
30
will work on a dumb filesystem without actual locking primitives.
 
31
 
 
32
This defines two classes: ReadLock and WriteLock, which can be
 
33
implemented in different ways on different platforms.  Both have an
 
34
unlock() method.
 
35
"""
 
36
 
 
37
 
 
38
import sys
 
39
import os
 
40
 
 
41
from bzrlib.trace import mutter, note, warning
 
42
from bzrlib.errors import LockError
 
43
 
 
44
class _base_Lock(object):
 
45
    def _open(self, filename, filemode):
 
46
        import errno
 
47
        try:
 
48
            self.f = open(filename, filemode)
 
49
            return self.f
 
50
        except IOError, e:
 
51
            if e.errno != errno.ENOENT:
 
52
                raise
 
53
 
 
54
            # maybe this is an old branch (before may 2005)
 
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            mutter("trying to create missing branch lock %r" % filename)
 
56
            
 
57
            self.f = open(filename, 'wb')
 
58
            return self.f
 
59
 
 
60
 
 
61
    def __del__(self):
 
62
        if self.f:
 
63
            from warnings import warn
 
64
            warn("lock on %r not released" % self.f)
 
65
            self.unlock()
 
66
            
 
67
 
 
68
    def unlock(self):
 
69
        raise NotImplementedError()
 
70
 
 
71
        
 
72
 
 
73
 
 
74
 
 
75
 
 
76
############################################################
 
77
# msvcrt locks
 
78
 
 
79
 
 
80
try:
 
81
    import fcntl
 
82
 
 
83
    class _fcntl_FileLock(_base_Lock):
 
84
        f = None
 
85
 
 
86
        def unlock(self):
 
87
            fcntl.lockf(self.f, fcntl.LOCK_UN)
 
88
            self.f.close()
 
89
            del self.f 
 
90
 
 
91
 
 
92
    class _fcntl_WriteLock(_fcntl_FileLock):
 
93
        def __init__(self, filename):
 
94
            try:
 
95
                fcntl.lockf(self._open(filename, 'wb'), fcntl.LOCK_EX)
 
96
            except Exception, e:
 
97
                raise LockError(e)
 
98
 
 
99
 
 
100
    class _fcntl_ReadLock(_fcntl_FileLock):
 
101
        def __init__(self, filename):
 
102
            try:
 
103
                fcntl.lockf(self._open(filename, 'rb'), fcntl.LOCK_SH)
 
104
            except Exception, e:
 
105
                raise LockError(e)
 
106
 
 
107
    WriteLock = _fcntl_WriteLock
 
108
    ReadLock = _fcntl_ReadLock
 
109
 
 
110
except ImportError:
 
111
    try:
 
112
        import win32con, win32file, pywintypes
 
113
 
 
114
 
 
115
        #LOCK_SH = 0 # the default
 
116
        #LOCK_EX = win32con.LOCKFILE_EXCLUSIVE_LOCK
 
117
        #LOCK_NB = win32con.LOCKFILE_FAIL_IMMEDIATELY
 
118
 
 
119
        class _w32c_FileLock(_base_Lock):
 
120
            def _lock(self, filename, openmode, lockmode):
 
121
                try:
 
122
                    self._open(filename, openmode)
 
123
                    self.hfile = win32file._get_osfhandle(self.f.fileno())
 
124
                    overlapped = pywintypes.OVERLAPPED()
 
125
                    win32file.LockFileEx(self.hfile, lockmode, 0, 0x7fff0000, overlapped)
 
126
                except Exception, e:
 
127
                    raise LockError(e)
 
128
 
 
129
            def unlock(self):
 
130
                try:
 
131
                    overlapped = pywintypes.OVERLAPPED()
 
132
                    win32file.UnlockFileEx(self.hfile, 0, 0x7fff0000, overlapped)
 
133
                    self.f.close()
 
134
                    self.f = None
 
135
                except Exception, e:
 
136
                    raise LockError(e)
 
137
 
 
138
 
 
139
 
 
140
        class _w32c_ReadLock(_w32c_FileLock):
 
141
            def __init__(self, filename):
 
142
                _w32c_FileLock._lock(self, filename, 'rb', 0)
 
143
 
 
144
        class _w32c_WriteLock(_w32c_FileLock):
 
145
            def __init__(self, filename):
 
146
                _w32c_FileLock._lock(self, filename, 'wb',
 
147
                                     win32con.LOCKFILE_EXCLUSIVE_LOCK)
 
148
 
 
149
 
 
150
 
 
151
        WriteLock = _w32c_WriteLock
 
152
        ReadLock = _w32c_ReadLock
 
153
 
 
154
    except ImportError:
 
155
        try:
 
156
            import msvcrt
 
157
 
 
158
 
 
159
            # Unfortunately, msvcrt.locking() doesn't distinguish between
 
160
            # read locks and write locks. Also, the way the combinations
 
161
            # work to get non-blocking is not the same, so we
 
162
            # have to write extra special functions here.
 
163
 
 
164
 
 
165
            class _msvc_FileLock(_base_Lock):
 
166
                LOCK_SH = 1
 
167
                LOCK_EX = 2
 
168
                LOCK_NB = 4
 
169
                def unlock(self):
 
170
                    _msvc_unlock(self.f)
 
171
                    self.f.close()
 
172
                    self.f = None
 
173
 
 
174
 
 
175
            class _msvc_ReadLock(_msvc_FileLock):
 
176
                def __init__(self, filename):
 
177
                    _msvc_lock(self._open(filename, 'rb'), self.LOCK_SH)
 
178
 
 
179
 
 
180
            class _msvc_WriteLock(_msvc_FileLock):
 
181
                def __init__(self, filename):
 
182
                    _msvc_lock(self._open(filename, 'wb'), self.LOCK_EX)
 
183
 
 
184
 
 
185
 
 
186
            def _msvc_lock(f, flags):
 
187
                try:
 
188
                    # Unfortunately, msvcrt.LK_RLCK is equivalent to msvcrt.LK_LOCK
 
189
                    # according to the comments, LK_RLCK is open the lock for writing.
 
190
 
 
191
                    # Unfortunately, msvcrt.locking() also has the side effect that it
 
192
                    # will only block for 10 seconds at most, and then it will throw an
 
193
                    # exception, this isn't terrible, though.
 
194
                    if type(f) == file:
 
195
                        fpos = f.tell()
 
196
                        fn = f.fileno()
 
197
                        f.seek(0)
 
198
                    else:
 
199
                        fn = f
 
200
                        fpos = os.lseek(fn, 0,0)
 
201
                        os.lseek(fn, 0,0)
 
202
 
 
203
                    if flags & _msvc_FileLock.LOCK_SH:
 
204
                        if flags & _msvc_FileLock.LOCK_NB:
 
205
                            lock_mode = msvcrt.LK_NBLCK
 
206
                        else:
 
207
                            lock_mode = msvcrt.LK_LOCK
 
208
                    elif flags & _msvc_FileLock.LOCK_EX:
 
209
                        if flags & _msvc_FileLock.LOCK_NB:
 
210
                            lock_mode = msvcrt.LK_NBRLCK
 
211
                        else:
 
212
                            lock_mode = msvcrt.LK_RLCK
 
213
                    else:
 
214
                        raise ValueError('Invalid lock mode: %r' % flags)
 
215
                    try:
 
216
                        msvcrt.locking(fn, lock_mode, -1)
 
217
                    finally:
 
218
                        os.lseek(fn, fpos, 0)
 
219
                except Exception, e:
 
220
                    raise LockError(e)
 
221
 
 
222
            def _msvc_unlock(f):
 
223
                try:
 
224
                    if type(f) == file:
 
225
                        fpos = f.tell()
 
226
                        fn = f.fileno()
 
227
                        f.seek(0)
 
228
                    else:
 
229
                        fn = f
 
230
                        fpos = os.lseek(fn, 0,0)
 
231
                        os.lseek(fn, 0,0)
 
232
 
 
233
                    try:
 
234
                        msvcrt.locking(fn, msvcrt.LK_UNLCK, -1)
 
235
                    finally:
 
236
                        os.lseek(fn, fpos, 0)
 
237
                except Exception, e:
 
238
                    raise LockError(e)
 
239
 
 
240
 
 
241
 
 
242
            WriteLock = _msvc_WriteLock
 
243
            ReadLock = _msvc_ReadLock
 
244
        except ImportError:
 
245
            raise NotImplementedError("please write a locking method "
 
246
                                      "for platform %r" % sys.platform)
 
247
 
 
248
 
 
249
 
 
250
 
 
251
 
 
252
 
 
253