C///

\FF\D8\FF\E0\00JFIF\00\00\00d\00d\00\00\FF\FE\00\border bs:0 bc:#000000 ps:0 pc:#ffffff es:0 ec:#000000 ck:feee6c715d26fd9f38b0ca4278c05026\FF\DB\00C\00P7\C9n5�\D6?\BD�\9Ds\EBp\9F[`8m\B7)o\B5\E8\E6I\99\FE3]]A2\BA\8Cw\D6E\93\\DEv\C8\009\F2\F1NI?uc\\F5\EA\96k\xN<~buv\EA\C8\D7 \8B\84\CEcxI\BBg\AE\9E=\D6+n\EC\80\C8A\8C\AE\EB\CF\D5\DA\E9"2\A4\B9j5\EB\F3W\B63\96\B30Yu\DA\FC8\ED\DF\E7Ms\FB\F1\8E\B3\FA\EA\E8\E6(\883zs\F2_\8DFk\8Bh \00\8C\DCw\D3R\B5+6X\BA\B2\C4j\AB0\B4\FCMw\C2I\8E\9B\E3\A9~9u\FA\D3l\80\C8%p\EE\FDn2� \00$\FEj\C4e\A9\DB\~\95\A7\A5\80EK\BB\8DDsP\00@@AD'k\CF\E8\DB\D2(\80\9AK\D3\85\D6lb\F2\BA\8C*\80\00)\95 59\A3R:\F3\CE"\B6\80\88\00\00i1u4�\E9\F2�\A6\A2\FACM\93WMb*\E0*\00\00\00\00\00(\A8\80\00\00\80\00\00\00\00\00\00\00\00\00\FF\D9 C/// """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." 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." - 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." - To release a write lock: - remove the file "#cvs.wfl." - rmdir the meta-lock - To release a read lock: - remove the file "#cvs.rfl." 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, 0777) return except os.error, msg: self.lockdir = None if msg[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], 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 WriteL