| 1 | # -*- test-case-name: twisted.test.test_lockfile -*- |
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| 2 | # Copyright (c) 2005 Divmod, Inc. |
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| 3 | # Copyright (c) Twisted Matrix Laboratories. |
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| 4 | # See LICENSE for details. |
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| 5 | |
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| 6 | """ |
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| 7 | Filesystem-based interprocess mutex. |
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| 8 | """ |
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| 9 | |
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| 10 | __metaclass__ = type |
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| 11 | |
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| 12 | import errno, os |
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| 13 | |
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| 14 | from time import time as _uniquefloat |
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| 15 | |
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| 16 | from twisted.python.runtime import platform |
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| 17 | |
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| 18 | def unique(): |
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| 19 | return str(long(_uniquefloat() * 1000)) |
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| 20 | |
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| 21 | from os import rename |
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| 22 | if not platform.isWindows(): |
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| 23 | from os import kill |
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| 24 | from os import symlink |
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| 25 | from os import readlink |
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| 26 | from os import remove as rmlink |
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| 27 | _windows = False |
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| 28 | else: |
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| 29 | _windows = True |
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| 30 | |
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| 31 | try: |
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| 32 | from win32api import OpenProcess |
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| 33 | import pywintypes |
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| 34 | except ImportError: |
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| 35 | kill = None |
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| 36 | else: |
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| 37 | ERROR_ACCESS_DENIED = 5 |
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| 38 | ERROR_INVALID_PARAMETER = 87 |
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| 39 | |
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| 40 | def kill(pid, signal): |
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| 41 | try: |
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| 42 | OpenProcess(0, 0, pid) |
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| 43 | except pywintypes.error, e: |
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| 44 | if e.args[0] == ERROR_ACCESS_DENIED: |
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| 45 | return |
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| 46 | elif e.args[0] == ERROR_INVALID_PARAMETER: |
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| 47 | raise OSError(errno.ESRCH, None) |
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| 48 | raise |
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| 49 | else: |
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| 50 | raise RuntimeError("OpenProcess is required to fail.") |
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| 51 | |
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| 52 | _open = file |
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| 53 | |
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| 54 | # XXX Implement an atomic thingamajig for win32 |
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| 55 | def symlink(value, filename): |
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| 56 | newlinkname = filename+"."+unique()+'.newlink' |
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| 57 | newvalname = os.path.join(newlinkname,"symlink") |
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| 58 | os.mkdir(newlinkname) |
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| 59 | f = _open(newvalname,'wcb') |
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| 60 | f.write(value) |
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| 61 | f.flush() |
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| 62 | f.close() |
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| 63 | try: |
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| 64 | rename(newlinkname, filename) |
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| 65 | except: |
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| 66 | os.remove(newvalname) |
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| 67 | os.rmdir(newlinkname) |
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| 68 | raise |
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| 69 | |
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| 70 | def readlink(filename): |
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| 71 | try: |
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| 72 | fObj = _open(os.path.join(filename,'symlink'), 'rb') |
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| 73 | except IOError, e: |
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| 74 | if e.errno == errno.ENOENT or e.errno == errno.EIO: |
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| 75 | raise OSError(e.errno, None) |
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| 76 | raise |
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| 77 | else: |
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| 78 | result = fObj.read() |
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| 79 | fObj.close() |
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| 80 | return result |
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| 81 | |
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| 82 | def rmlink(filename): |
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| 83 | os.remove(os.path.join(filename, 'symlink')) |
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| 84 | os.rmdir(filename) |
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| 85 | |
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| 86 | |
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| 87 | |
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| 88 | class FilesystemLock: |
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| 89 | """ |
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| 90 | A mutex. |
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| 91 | |
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| 92 | This relies on the filesystem property that creating |
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| 93 | a symlink is an atomic operation and that it will |
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| 94 | fail if the symlink already exists. Deleting the |
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| 95 | symlink will release the lock. |
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| 96 | |
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| 97 | @ivar name: The name of the file associated with this lock. |
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| 98 | |
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| 99 | @ivar clean: Indicates whether this lock was released cleanly by its |
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| 100 | last owner. Only meaningful after C{lock} has been called and |
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| 101 | returns True. |
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| 102 | |
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| 103 | @ivar locked: Indicates whether the lock is currently held by this |
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| 104 | object. |
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| 105 | """ |
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| 106 | |
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| 107 | clean = None |
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| 108 | locked = False |
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| 109 | |
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| 110 | def __init__(self, name): |
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| 111 | self.name = name |
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| 112 | |
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| 113 | |
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| 114 | def lock(self): |
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| 115 | """ |
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| 116 | Acquire this lock. |
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| 117 | |
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| 118 | @rtype: C{bool} |
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| 119 | @return: True if the lock is acquired, false otherwise. |
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| 120 | |
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| 121 | @raise: Any exception os.symlink() may raise, other than |
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| 122 | EEXIST. |
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| 123 | """ |
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| 124 | clean = True |
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| 125 | while True: |
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| 126 | try: |
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| 127 | symlink(str(os.getpid()), self.name) |
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| 128 | except OSError, e: |
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| 129 | if _windows and e.errno in (errno.EACCES, errno.EIO): |
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| 130 | # The lock is in the middle of being deleted because we're |
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| 131 | # on Windows where lock removal isn't atomic. Give up, we |
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| 132 | # don't know how long this is going to take. |
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| 133 | return False |
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| 134 | if e.errno == errno.EEXIST: |
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| 135 | try: |
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| 136 | pid = readlink(self.name) |
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| 137 | except OSError, e: |
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| 138 | if e.errno == errno.ENOENT: |
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| 139 | # The lock has vanished, try to claim it in the |
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| 140 | # next iteration through the loop. |
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| 141 | continue |
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| 142 | raise |
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| 143 | except IOError, e: |
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| 144 | if _windows and e.errno == errno.EACCES: |
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| 145 | # The lock is in the middle of being |
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| 146 | # deleted because we're on Windows where |
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| 147 | # lock removal isn't atomic. Give up, we |
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| 148 | # don't know how long this is going to |
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| 149 | # take. |
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| 150 | return False |
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| 151 | raise |
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| 152 | try: |
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| 153 | if kill is not None: |
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| 154 | kill(int(pid), 0) |
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| 155 | except OSError, e: |
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| 156 | if e.errno == errno.ESRCH: |
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| 157 | # The owner has vanished, try to claim it in the next |
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| 158 | # iteration through the loop. |
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| 159 | try: |
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| 160 | rmlink(self.name) |
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| 161 | except OSError, e: |
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| 162 | if e.errno == errno.ENOENT: |
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| 163 | # Another process cleaned up the lock. |
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| 164 | # Race them to acquire it in the next |
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| 165 | # iteration through the loop. |
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| 166 | continue |
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| 167 | raise |
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| 168 | clean = False |
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| 169 | continue |
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| 170 | raise |
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| 171 | return False |
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| 172 | raise |
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| 173 | self.locked = True |
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| 174 | self.clean = clean |
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| 175 | return True |
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| 176 | |
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| 177 | |
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| 178 | def unlock(self): |
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| 179 | """ |
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| 180 | Release this lock. |
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| 181 | |
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| 182 | This deletes the directory with the given name. |
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| 183 | |
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| 184 | @raise: Any exception os.readlink() may raise, or |
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| 185 | ValueError if the lock is not owned by this process. |
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| 186 | """ |
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| 187 | pid = readlink(self.name) |
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| 188 | if int(pid) != os.getpid(): |
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| 189 | raise ValueError("Lock %r not owned by this process" % (self.name,)) |
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| 190 | rmlink(self.name) |
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| 191 | self.locked = False |
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| 192 | |
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| 193 | |
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| 194 | def isLocked(name): |
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| 195 | """Determine if the lock of the given name is held or not. |
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| 196 | |
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| 197 | @type name: C{str} |
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| 198 | @param name: The filesystem path to the lock to test |
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| 199 | |
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| 200 | @rtype: C{bool} |
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| 201 | @return: True if the lock is held, False otherwise. |
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| 202 | """ |
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| 203 | l = FilesystemLock(name) |
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| 204 | result = None |
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| 205 | try: |
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| 206 | result = l.lock() |
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| 207 | finally: |
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| 208 | if result: |
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| 209 | l.unlock() |
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| 210 | return not result |
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| 211 | |
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| 212 | |
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| 213 | __all__ = ['FilesystemLock', 'isLocked'] |
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