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Commit1b3fedd

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LockFile: id representing the instance that keeps the lock is unique now - locks will check whether the lock they wrote truly is theirs - in case threads are racing, this might not be the case. Now this issue will be detected and results in a proper failure
1 parentdcf2c3b commit1b3fedd

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1 file changed

+25
-11
lines changed

1 file changed

+25
-11
lines changed

‎lib/git/utils.py

Lines changed: 25 additions & 11 deletions
Original file line numberDiff line numberDiff line change
@@ -119,6 +119,10 @@ def _lock_file_path(self):
119119
"""
120120
return"%s.lock"% (self._file_path)
121121

122+
def_get_id(self):
123+
"""Returns string id to be written into the lock file"""
124+
return"%i|%i"% (os.getpid(),hash(self))
125+
122126
def_has_lock(self):
123127
"""
124128
Return
@@ -133,13 +137,13 @@ def _has_lock(self):
133137
lock_file=self._lock_file_path()
134138
try:
135139
fp=open(lock_file,"rb")
136-
pid=int(fp.read())
140+
pid=fp.read()
137141
fp.close()
138142
exceptIOError:
139143
raiseAssertionError("The lock file at %s could not be read"%lock_file)
140144

141-
ifpid!=os.getpid():
142-
raiseAssertionError("We claim to own the lock at %s, but it was not owned by our process %i, but by %i"% (lock_file,os.getpid(),pid))
145+
ifpid!=self._get_id():
146+
raiseAssertionError("We claim to own the lock at %s, but it was not owned by our process %r, but by %r"% (lock_file,self._get_id(),pid))
143147

144148
returnTrue
145149

@@ -152,14 +156,25 @@ def _obtain_lock_or_raise(self):
152156
"""
153157
ifself._has_lock():
154158
return
155-
156159
lock_file=self._lock_file_path()
157-
ifos.path.exists(lock_file):
160+
ifos.path.isfile(lock_file):
158161
raiseIOError("Lock for file %r did already exist, delete %r in case the lock is illegal"% (self._file_path,lock_file))
159-
162+
163+
my_id=self._get_id()
160164
fp=open(lock_file,"wb")
161-
fp.write(str(os.getpid()))
165+
fp.write(my_id)
166+
fp.close()
167+
168+
# verify its truly us who got the lock - if two threads are doing this within the
169+
# fraction of a millisecond, it is possible to actually trick the FS
170+
# and two threads write, but only one succeeds.
171+
fp=open(lock_file,'rb')
172+
actual_id=fp.read()
162173
fp.close()
174+
ifactual_id!=my_id:
175+
msg="Failed to obtain lock for file %r as the process identified by %r outraced this process or thread %r"% (self._file_path,actual_id,my_id)
176+
raiseIOError(msg)
177+
# END verification
163178

164179
self._owns_lock=True
165180

@@ -175,11 +190,11 @@ def _release_lock(self):
175190
Release our lock if we have one
176191
"""
177192
ifnotself._has_lock():
178-
return
179-
193+
return
180194
os.remove(self._lock_file_path())
181195
self._owns_lock=False
182196

197+
183198
classBlockingLockFile(LockFile):
184199
"""The lock file will block until a lock could be obtained, or fail after
185200
a specified timeout"""
@@ -206,7 +221,7 @@ def _obtain_lock(self):
206221
maxtime=starttime+float(self._max_block_time)
207222
whileTrue:
208223
try:
209-
self._obtain_lock_or_raise()
224+
super(BlockingLockFile,self)._obtain_lock()
210225
exceptIOError:
211226
curtime=time.time()
212227
ifcurtime>=maxtime:
@@ -219,7 +234,6 @@ def _obtain_lock(self):
219234
# END endless loop
220235

221236

222-
223237
classConcurrentWriteOperation(LockFile):
224238
"""
225239
This class facilitates a safe write operation to a file on disk such that we:

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