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1 # lock.py - simple locking scheme for mercurial
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2 #
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3 # Copyright 2005, 2006 Matt Mackall <mpm@selenic.com>
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4 #
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5 # This software may be used and distributed according to the terms of the
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6 # GNU General Public License version 2, incorporated herein by reference.
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7
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8 import util, error
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9 import errno, os, socket, time
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10 import warnings
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11
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12 class lock(object):
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13 # lock is symlink on platforms that support it, file on others.
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14
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15 # symlink is used because create of directory entry and contents
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16 # are atomic even over nfs.
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17
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18 # old-style lock: symlink to pid
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19 # new-style lock: symlink to hostname:pid
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20
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21 _host = None
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22
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23 def __init__(self, file, timeout=-1, releasefn=None, desc=None):
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24 self.f = file
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25 self.held = 0
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26 self.timeout = timeout
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27 self.releasefn = releasefn
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28 self.desc = desc
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29 self.lock()
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30
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31 def __del__(self):
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32 if self.held:
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33 warnings.warn("use lock.release instead of del lock",
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34 category=DeprecationWarning,
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35 stacklevel=2)
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36
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37 # ensure the lock will be removed
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38 # even if recursive locking did occur
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39 self.held = 1
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40
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41 self.release()
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42
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43 def lock(self):
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44 timeout = self.timeout
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45 while 1:
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46 try:
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47 self.trylock()
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48 return 1
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49 except error.LockHeld, inst:
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50 if timeout != 0:
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51 time.sleep(1)
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52 if timeout > 0:
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53 timeout -= 1
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54 continue
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55 raise error.LockHeld(errno.ETIMEDOUT, inst.filename, self.desc,
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56 inst.locker)
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57
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58 def trylock(self):
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59 if self.held:
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60 self.held += 1
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61 return
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62 if lock._host is None:
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63 lock._host = socket.gethostname()
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64 lockname = '%s:%s' % (lock._host, os.getpid())
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65 while not self.held:
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66 try:
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67 util.makelock(lockname, self.f)
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68 self.held = 1
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69 except (OSError, IOError), why:
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70 if why.errno == errno.EEXIST:
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71 locker = self.testlock()
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72 if locker is not None:
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73 raise error.LockHeld(errno.EAGAIN, self.f, self.desc,
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74 locker)
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75 else:
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76 raise error.LockUnavailable(why.errno, why.strerror,
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77 why.filename, self.desc)
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78
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79 def testlock(self):
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80 """return id of locker if lock is valid, else None.
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81
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82 If old-style lock, we cannot tell what machine locker is on.
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83 with new-style lock, if locker is on this machine, we can
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84 see if locker is alive. If locker is on this machine but
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85 not alive, we can safely break lock.
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86
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87 The lock file is only deleted when None is returned.
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88
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89 """
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90 locker = util.readlock(self.f)
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91 try:
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92 host, pid = locker.split(":", 1)
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93 except ValueError:
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94 return locker
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95 if host != lock._host:
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96 return locker
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97 try:
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98 pid = int(pid)
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99 except:
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100 return locker
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101 if util.testpid(pid):
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102 return locker
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103 # if locker dead, break lock. must do this with another lock
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104 # held, or can race and break valid lock.
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105 try:
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106 l = lock(self.f + '.break')
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107 l.trylock()
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108 os.unlink(self.f)
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109 l.release()
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110 except error.LockError:
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111 return locker
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112
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113 def release(self):
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114 if self.held > 1:
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115 self.held -= 1
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116 elif self.held is 1:
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117 self.held = 0
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118 if self.releasefn:
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119 self.releasefn()
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120 try:
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121 os.unlink(self.f)
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122 except: pass
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123
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124 def release(*locks):
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125 for lock in locks:
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126 if lock is not None:
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127 lock.release()
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128
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