Mercurial > hg > pyhgsh

annotate mercurial/lock.py @ 2016:ff5c9a92f556

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fix backtrace printed when cannot get lock. change lock error handling code so exceptions have useful info and exception handling in one place. add test case for when cannot get lock.
author Vadim Gelfer <vadim.gelfer@gmail.com>
date Tue, 28 Mar 2006 09:01:07 -0800
parents d314a89fa4f1
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 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 c = locker.find(':')
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89 if c == -1:
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90 return locker
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91 host = locker[:c]
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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(locker[c+1:])
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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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109
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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