annotate mercurial/lock.py @ 3420:52617d992eed

Report branch for hg log and friends
author Matt Mackall <mpm@selenic.com>
date Tue, 17 Oct 2006 18:30:18 -0500
parents 345bac2bc4ec
children
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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
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6 # of the GNU General Public License, incorporated herein by reference.
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7
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8 from demandload import *
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9 demandload(globals(), 'errno os socket time util')
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10
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11 class LockException(IOError):
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12 def __init__(self, errno, strerror, filename, desc):
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13 IOError.__init__(self, errno, strerror, filename)
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14 self.desc = desc
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15
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16 class LockHeld(LockException):
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17 def __init__(self, errno, filename, desc, locker):
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18 LockException.__init__(self, errno, 'Lock held', filename, desc)
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19 self.locker = locker
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20
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21 class LockUnavailable(LockException):
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22 pass
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23
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24 class lock(object):
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25 # lock is symlink on platforms that support it, file on others.
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26
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27 # symlink is used because create of directory entry and contents
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28 # are atomic even over nfs.
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29
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30 # old-style lock: symlink to pid
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31 # new-style lock: symlink to hostname:pid
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32
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33 def __init__(self, file, timeout=-1, releasefn=None, desc=None):
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34 self.f = file
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35 self.held = 0
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36 self.timeout = timeout
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37 self.releasefn = releasefn
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38 self.id = None
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39 self.host = None
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40 self.pid = None
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41 self.desc = desc
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42 self.lock()
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43
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44 def __del__(self):
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45 self.release()
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46
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47 def lock(self):
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48 timeout = self.timeout
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49 while 1:
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50 try:
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51 self.trylock()
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52 return 1
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53 except LockHeld, inst:
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54 if timeout != 0:
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55 time.sleep(1)
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56 if timeout > 0:
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57 timeout -= 1
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58 continue
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59 raise LockHeld(errno.ETIMEDOUT, inst.filename, self.desc,
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60 inst.locker)
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61
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62 def trylock(self):
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63 if self.id is None:
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64 self.host = socket.gethostname()
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65 self.pid = os.getpid()
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66 self.id = '%s:%s' % (self.host, self.pid)
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67 while not self.held:
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68 try:
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69 util.makelock(self.id, self.f)
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70 self.held = 1
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71 except (OSError, IOError), why:
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72 if why.errno == errno.EEXIST:
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73 locker = self.testlock()
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74 if locker:
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75 raise LockHeld(errno.EAGAIN, self.f, self.desc,
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76 locker)
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77 else:
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78 raise LockUnavailable(why.errno, why.strerror,
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79 why.filename, self.desc)
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80
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81 def testlock(self):
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82 '''return id of locker if lock is valid, else None.'''
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83 # if old-style lock, we cannot tell what machine locker is on.
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84 # with new-style lock, if locker is on this machine, we can
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85 # see if locker is alive. if locker is on this machine but
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86 # not alive, we can safely break lock.
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87 locker = util.readlock(self.f)
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88 try:
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89 host, pid = locker.split(":", 1)
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90 except ValueError:
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91 return locker
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92 if host != self.host:
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93 return locker
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94 try:
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95 pid = int(pid)
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96 except:
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97 return locker
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98 if util.testpid(pid):
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99 return locker
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100 # if locker dead, break lock. must do this with another lock
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101 # held, or can race and break valid lock.
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102 try:
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103 l = lock(self.f + '.break')
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104 l.trylock()
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105 os.unlink(self.f)
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106 l.release()
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107 except (LockHeld, LockUnavailable):
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108 return locker
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110 def release(self):
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111 if self.held:
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112 self.held = 0
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113 if self.releasefn:
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114 self.releasefn()
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115 try:
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116 os.unlink(self.f)
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117 except: pass
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118