EmbeddedPkg: Extend NvVarStoreFormattedLib LIBRARY_CLASS

[mirror_edk2.git] / AppPkg / Applications / Python / Python-2.7.2 / Demo / pdist / cvslock.py

"""CVS locking algorithm.\r
\r
CVS locking strategy\r
====================\r
\r
As reverse engineered from the CVS 1.3 sources (file lock.c):\r
\r
- Locking is done on a per repository basis (but a process can hold\r
write locks for multiple directories); all lock files are placed in\r
the repository and have names beginning with "#cvs.".\r
\r
- Before even attempting to lock, a file "#cvs.tfl.<pid>" is created\r
(and removed again), to test that we can write the repository.  [The\r
algorithm can still be fooled (1) if the repository's mode is changed\r
while attempting to lock; (2) if this file exists and is writable but\r
the directory is not.]\r
\r
- While creating the actual read/write lock files (which may exist for\r
a long time), a "meta-lock" is held.  The meta-lock is a directory\r
named "#cvs.lock" in the repository.  The meta-lock is also held while\r
a write lock is held.\r
\r
- To set a read lock:\r
\r
        - acquire the meta-lock\r
        - create the file "#cvs.rfl.<pid>"\r
        - release the meta-lock\r
\r
- To set a write lock:\r
\r
        - acquire the meta-lock\r
        - check that there are no files called "#cvs.rfl.*"\r
                - if there are, release the meta-lock, sleep, try again\r
        - create the file "#cvs.wfl.<pid>"\r
\r
- To release a write lock:\r
\r
        - remove the file "#cvs.wfl.<pid>"\r
        - rmdir the meta-lock\r
\r
- To release a read lock:\r
\r
        - remove the file "#cvs.rfl.<pid>"\r
\r
\r
Additional notes\r
----------------\r
\r
- A process should read-lock at most one repository at a time.\r
\r
- A process may write-lock as many repositories as it wishes (to avoid\r
deadlocks, I presume it should always lock them top-down in the\r
directory hierarchy).\r
\r
- A process should make sure it removes all its lock files and\r
directories when it crashes.\r
\r
- Limitation: one user id should not be committing files into the same\r
repository at the same time.\r
\r
\r
Turn this into Python code\r
--------------------------\r
\r
rl = ReadLock(repository, waittime)\r
\r
wl = WriteLock(repository, waittime)\r
\r
list = MultipleWriteLock([repository1, repository2, ...], waittime)\r
\r
"""\r
\r
\r
import os\r
import time\r
import stat\r
import pwd\r
\r
\r
# Default wait time\r
DELAY = 10\r
\r
\r
# XXX This should be the same on all Unix versions\r
EEXIST = 17\r
\r
\r
# Files used for locking (must match cvs.h in the CVS sources)\r
CVSLCK = "#cvs.lck"\r
CVSRFL = "#cvs.rfl."\r
CVSWFL = "#cvs.wfl."\r
\r
\r
class Error:\r
\r
    def __init__(self, msg):\r
        self.msg = msg\r
\r
    def __repr__(self):\r
        return repr(self.msg)\r
\r
    def __str__(self):\r
        return str(self.msg)\r
\r
\r
class Locked(Error):\r
    pass\r
\r
\r
class Lock:\r
\r
    def __init__(self, repository = ".", delay = DELAY):\r
        self.repository = repository\r
        self.delay = delay\r
        self.lockdir = None\r
        self.lockfile = None\r
        pid = repr(os.getpid())\r
        self.cvslck = self.join(CVSLCK)\r
        self.cvsrfl = self.join(CVSRFL + pid)\r
        self.cvswfl = self.join(CVSWFL + pid)\r
\r
    def __del__(self):\r
        print "__del__"\r
        self.unlock()\r
\r
    def setlockdir(self):\r
        while 1:\r
            try:\r
                self.lockdir = self.cvslck\r
                os.mkdir(self.cvslck, 0777)\r
                return\r
            except os.error, msg:\r
                self.lockdir = None\r
                if msg[0] == EEXIST:\r
                    try:\r
                        st = os.stat(self.cvslck)\r
                    except os.error:\r
                        continue\r
                    self.sleep(st)\r
                    continue\r
                raise Error("failed to lock %s: %s" % (\r
                        self.repository, msg))\r
\r
    def unlock(self):\r
        self.unlockfile()\r
        self.unlockdir()\r
\r
    def unlockfile(self):\r
        if self.lockfile:\r
            print "unlink", self.lockfile\r
            try:\r
                os.unlink(self.lockfile)\r
            except os.error:\r
                pass\r
            self.lockfile = None\r
\r
    def unlockdir(self):\r
        if self.lockdir:\r
            print "rmdir", self.lockdir\r
            try:\r
                os.rmdir(self.lockdir)\r
            except os.error:\r
                pass\r
            self.lockdir = None\r
\r
    def sleep(self, st):\r
        sleep(st, self.repository, self.delay)\r
\r
    def join(self, name):\r
        return os.path.join(self.repository, name)\r
\r
\r
def sleep(st, repository, delay):\r
    if delay <= 0:\r
        raise Locked(st)\r
    uid = st[stat.ST_UID]\r
    try:\r
        pwent = pwd.getpwuid(uid)\r
        user = pwent[0]\r
    except KeyError:\r
        user = "uid %d" % uid\r
    print "[%s]" % time.ctime(time.time())[11:19],\r
    print "Waiting for %s's lock in" % user, repository\r
    time.sleep(delay)\r
\r
\r
class ReadLock(Lock):\r
\r
    def __init__(self, repository, delay = DELAY):\r
        Lock.__init__(self, repository, delay)\r
        ok = 0\r
        try:\r
            self.setlockdir()\r
            self.lockfile = self.cvsrfl\r
            fp = open(self.lockfile, 'w')\r
            fp.close()\r
            ok = 1\r
        finally:\r
            if not ok:\r
                self.unlockfile()\r
            self.unlockdir()\r
\r
\r
class WriteLock(Lock):\r
\r
    def __init__(self, repository, delay = DELAY):\r
        Lock.__init__(self, repository, delay)\r
        self.setlockdir()\r
        while 1:\r
            uid = self.readers_exist()\r
            if not uid:\r
                break\r
            self.unlockdir()\r
            self.sleep(uid)\r
        self.lockfile = self.cvswfl\r
        fp = open(self.lockfile, 'w')\r
        fp.close()\r
\r
    def readers_exist(self):\r
        n = len(CVSRFL)\r
        for name in os.listdir(self.repository):\r
            if name[:n] == CVSRFL:\r
                try:\r
                    st = os.stat(self.join(name))\r
                except os.error:\r
                    continue\r
                return st\r
        return None\r
\r
\r
def MultipleWriteLock(repositories, delay = DELAY):\r
    while 1:\r
        locks = []\r
        for r in repositories:\r
            try:\r
                locks.append(WriteLock(r, 0))\r
            except Locked, instance:\r
                del locks\r
                break\r
        else:\r
            break\r
        sleep(instance.msg, r, delay)\r
    return list\r
\r
\r
def test():\r
    import sys\r
    if sys.argv[1:]:\r
        repository = sys.argv[1]\r
    else:\r
        repository = "."\r
    rl = None\r
    wl = None\r
    try:\r
        print "attempting write lock ..."\r
        wl = WriteLock(repository)\r
        print "got it."\r
        wl.unlock()\r
        print "attempting read lock ..."\r
        rl = ReadLock(repository)\r
        print "got it."\r
        rl.unlock()\r
    finally:\r
        print [1]\r
        sys.exc_traceback = None\r
        print [2]\r
        if rl:\r
            rl.unlock()\r
        print [3]\r
        if wl:\r
            wl.unlock()\r
        print [4]\r
        rl = None\r
        print [5]\r
        wl = None\r
        print [6]\r
\r
\r
if __name__ == '__main__':\r
    test()\r