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Diffstat (limited to 'Demo/pdist/cvslock.py')
| -rw-r--r-- | Demo/pdist/cvslock.py | 279 |
1 files changed, 0 insertions, 279 deletions
diff --git a/Demo/pdist/cvslock.py b/Demo/pdist/cvslock.py deleted file mode 100644 index ffaa15e..0000000 --- a/Demo/pdist/cvslock.py +++ /dev/null @@ -1,279 +0,0 @@ -"""CVS locking algorithm. - -CVS locking strategy -==================== - -As reverse engineered from the CVS 1.3 sources (file lock.c): - -- Locking is done on a per repository basis (but a process can hold -write locks for multiple directories); all lock files are placed in -the repository and have names beginning with "#cvs.". - -- Before even attempting to lock, a file "#cvs.tfl.<pid>" is created -(and removed again), to test that we can write the repository. [The -algorithm can still be fooled (1) if the repository's mode is changed -while attempting to lock; (2) if this file exists and is writable but -the directory is not.] - -- While creating the actual read/write lock files (which may exist for -a long time), a "meta-lock" is held. The meta-lock is a directory -named "#cvs.lock" in the repository. The meta-lock is also held while -a write lock is held. - -- To set a read lock: - - - acquire the meta-lock - - create the file "#cvs.rfl.<pid>" - - release the meta-lock - -- To set a write lock: - - - acquire the meta-lock - - check that there are no files called "#cvs.rfl.*" - - if there are, release the meta-lock, sleep, try again - - create the file "#cvs.wfl.<pid>" - -- To release a write lock: - - - remove the file "#cvs.wfl.<pid>" - - rmdir the meta-lock - -- To release a read lock: - - - remove the file "#cvs.rfl.<pid>" - - -Additional notes ----------------- - -- A process should read-lock at most one repository at a time. - -- A process may write-lock as many repositories as it wishes (to avoid -deadlocks, I presume it should always lock them top-down in the -directory hierarchy). - -- A process should make sure it removes all its lock files and -directories when it crashes. - -- Limitation: one user id should not be committing files into the same -repository at the same time. - - -Turn this into Python code --------------------------- - -rl = ReadLock(repository, waittime) - -wl = WriteLock(repository, waittime) - -list = MultipleWriteLock([repository1, repository2, ...], waittime) - -""" - - -import os -import time -import stat -import pwd - - -# Default wait time -DELAY = 10 - - -# XXX This should be the same on all Unix versions -EEXIST = 17 - - -# Files used for locking (must match cvs.h in the CVS sources) -CVSLCK = "#cvs.lck" -CVSRFL = "#cvs.rfl." -CVSWFL = "#cvs.wfl." - - -class Error: - - def __init__(self, msg): - self.msg = msg - - def __repr__(self): - return repr(self.msg) - - def __str__(self): - return str(self.msg) - - -class Locked(Error): - pass - - -class Lock: - - def __init__(self, repository = ".", delay = DELAY): - self.repository = repository - self.delay = delay - self.lockdir = None - self.lockfile = None - pid = repr(os.getpid()) - self.cvslck = self.join(CVSLCK) - self.cvsrfl = self.join(CVSRFL + pid) - self.cvswfl = self.join(CVSWFL + pid) - - def __del__(self): - print("__del__") - self.unlock() - - def setlockdir(self): - while 1: - try: - self.lockdir = self.cvslck - os.mkdir(self.cvslck, 0o777) - return - except os.error as msg: - self.lockdir = None - if msg.args[0] == EEXIST: - try: - st = os.stat(self.cvslck) - except os.error: - continue - self.sleep(st) - continue - raise Error("failed to lock %s: %s" % ( - self.repository, msg)) - - def unlock(self): - self.unlockfile() - self.unlockdir() - - def unlockfile(self): - if self.lockfile: - print("unlink", self.lockfile) - try: - os.unlink(self.lockfile) - except os.error: - pass - self.lockfile = None - - def unlockdir(self): - if self.lockdir: - print("rmdir", self.lockdir) - try: - os.rmdir(self.lockdir) - except os.error: - pass - self.lockdir = None - - def sleep(self, st): - sleep(st, self.repository, self.delay) - - def join(self, name): - return os.path.join(self.repository, name) - - -def sleep(st, repository, delay): - if delay <= 0: - raise Locked(st) - uid = st[stat.ST_UID] - try: - pwent = pwd.getpwuid(uid) - user = pwent[0] - except KeyError: - user = "uid %d" % uid - print("[%s]" % time.ctime(time.time())[11:19], end=' ') - print("Waiting for %s's lock in" % user, repository) - time.sleep(delay) - - -class ReadLock(Lock): - - def __init__(self, repository, delay = DELAY): - Lock.__init__(self, repository, delay) - ok = 0 - try: - self.setlockdir() - self.lockfile = self.cvsrfl - fp = open(self.lockfile, 'w') - fp.close() - ok = 1 - finally: - if not ok: - self.unlockfile() - self.unlockdir() - - -class WriteLock(Lock): - - def __init__(self, repository, delay = DELAY): - Lock.__init__(self, repository, delay) - self.setlockdir() - while 1: - uid = self.readers_exist() - if not uid: - break - self.unlockdir() - self.sleep(uid) - self.lockfile = self.cvswfl - fp = open(self.lockfile, 'w') - fp.close() - - def readers_exist(self): - n = len(CVSRFL) - for name in os.listdir(self.repository): - if name[:n] == CVSRFL: - try: - st = os.stat(self.join(name)) - except os.error: - continue - return st - return None - - -def MultipleWriteLock(repositories, delay = DELAY): - while 1: - locks = [] - for r in repositories: - try: - locks.append(WriteLock(r, 0)) - except Locked as instance: - del locks - break - else: - break - sleep(instance.msg, r, delay) - return list - - -def test(): - import sys - if sys.argv[1:]: - repository = sys.argv[1] - else: - repository = "." - rl = None - wl = None - try: - print("attempting write lock ...") - wl = WriteLock(repository) - print("got it.") - wl.unlock() - print("attempting read lock ...") - rl = ReadLock(repository) - print("got it.") - rl.unlock() - finally: - print([1]) - print([2]) - if rl: - rl.unlock() - print([3]) - if wl: - wl.unlock() - print([4]) - rl = None - print([5]) - wl = None - print([6]) - - -if __name__ == '__main__': - test() |