pylibmc/pylibmc.py

"""`python-memcached`-compatible wrapper around `_pylibmc`.

The interface is pretty much exactly the same as python-memcached, with some
minor differences. If you should happen to spot any, file a bug!

>>> import pylibmc
>>> mc = pylibmc.Client(["127.0.0.1"])
>>> b = mc.behaviors
>>> list(sorted(b.keys()))  # doctest: +NORMALIZE_WHITESPACE
['binary_protocol', 'buffer_requests', 'cache_lookups', 'connect_timeout',
 'distribution', 'hash', 'ketama', 'ketama_hash', 'ketama_weighted',
 'no block', 'poll_timeout', 'rcv_timeout', 'retry_timeout',
 'server_failure_limit', 'snd_timeout', 'socket recv size', 'socket send size',
 'sort_hosts', 'support_cas', 'tcp_nodelay', 'verify_key']
>>> b["hash"]
'default'
>>> b["hash"] = 'fnv1a_32'
>>> mc.behaviors["hash"]
'fnv1a_32'
>>> super(pylibmc.Client, mc).get_behaviors()["hash"]
6
"""

import _pylibmc

__all__ = ["hashers", "distributions", "Client"]
__version__ = _pylibmc.__version__

hashers, hashers_rvs = {}, {}
distributions, distributions_rvs = {}, {}
# Not the prettiest way of doing things, but works well.
for name in dir(_pylibmc):
    if name.startswith("hash_"):
        key, value = name[5:], getattr(_pylibmc, name)
        hashers[key] = value
        hashers_rvs[value] = key
    elif name.startswith("distribution_"):
        key, value = name[13:].replace("_", " "), getattr(_pylibmc, name)
        distributions[key] = value
        distributions_rvs[value] = key

class BehaviorDict(dict):
    def __init__(self, client, *args, **kwds):
        super(BehaviorDict, self).__init__(*args, **kwds)
        self.client = client

    def __setitem__(self, name, value):
        super(BehaviorDict, self).__setitem__(name, value)
        self.client.set_behaviors({name: value})

    def update(self, *args, **kwds):
        super(BehaviorDict, self).update(*args, **kwds)
        self.client.set_behaviors(self.copy())

class Client(_pylibmc.client):
    def __init__(self, servers, *args, **kwds):
        """Initialize a memcached client instance.

        This connects to the servers in *servers*, which will default to being
        TCP servers. If it looks like a filesystem path, a UNIX socket. If
        prefixed with `udp:`, a UDP connection.
        """
        addr_tups = []
        for server in servers:
            addr = server
            port = 11211
            if server.startswith("udp:"):
                stype = _pylibmc.server_type_udp
                addr = addr[4:]
                if ":" in server:
                    (addr, port) = addr.split(":", 1)
                    port = int(port)
            elif ":" in server:
                stype = _pylibmc.server_type_tcp
                (addr, port) = server.split(":", 1)
                port = int(port)
            elif "/" in server:
                stype = _pylibmc.server_type_unix
                port = 0
            else:
                stype = _pylibmc.server_type_tcp
            addr_tups.append((stype, addr, port))
        super(Client, self).__init__(addr_tups)

    def get_behaviors(self):
        """Gets the behaviors from the underlying C client instance.

        Reverses the integer constants for `hash` and `distribution` into more
        understandable string values. See *set_behaviors* for info.
        """
        behaviors = super(Client, self).get_behaviors()
        behaviors["hash"] = hashers_rvs[behaviors["hash"]]
        behaviors["distribution"] = distributions_rvs[behaviors["distribution"]]
        return BehaviorDict(self, behaviors)

    def set_behaviors(self, behaviors):
        """Sets the behaviors on the underlying C client instance.

        Takes care of morphing the `hash` key, if specified, into the
        corresponding integer constant (which the C client expects.) If,
        however, an unknown value is specified, it's passed on to the C client
        (where it most surely will error out.)

        This also happens for `distribution`.
        """
        behaviors = behaviors.copy()
        if behaviors.get("hash", None) in hashers:
            behaviors["hash"] = hashers[behaviors["hash"]]
        if behaviors.get("distribution") in distributions:
            behaviors["distribution"] = distributions[behaviors["distribution"]]
        return super(Client, self).set_behaviors(behaviors)

    behaviors = property(get_behaviors, set_behaviors)

from contextlib import contextmanager

class ClientPool(list):
    """Client pooling helper.

    This is mostly useful in threaded environments, because a client isn't
    thread-safe at all. Instead, what you want to do is have each thread use
    its own client, but you don't want to reconnect these all the time.

    The solution is a pool, and this class is a helper for that.

    >>> mc = Client(["127.0.0.1"])
    >>> pool = ClientPool()
    >>> pool.fill(mc, 4)
    >>> with pool.reserve() as mc:
    ...     mc.set("hi", "ho")
    ...     mc.delete("hi")
    ... 
    """

    @contextmanager
    def reserve(self):
        """Reserve a client, and put it back into the pool when done."""
        mc = self.pop()
        try:
            yield mc
        finally:
            self.append(mc)

    def fill(self, mc, n_slots):
        """Fill *n_slots* of the pool with clones of *mc*."""
        for i in xrange(n_slots):
            self.append(mc.clone())

class ThreadMappedPool(dict):
    """Much like the *ClientPool*, helps you with pooling.

    In a threaded environment, you'd most likely want to have a client per
    thread. And there'd be no harm in one thread keeping the same client at all
    times. So, why not map threads to clients? That's what this class does.

    If a client is reserved, this class checks for a key based on the current
    thread, and if none exists, clones the master client and inserts that key.

    >>> mc = Client(["127.0.0.1"])
    >>> pool = ThreadMappedPool(mc)
    >>> with pool.reserve() as mc:
    ...     mc.set("hi", "ho")
    ...     mc.delete("hi")
    ... 
    """

    def __new__(cls, master):
        return super(ThreadMappedPool, cls).__new__(cls)

    def __init__(self, master):
        self.master = master

    @contextmanager
    def reserve(self):
        """Reserve a client.

        Creates a new client based on the master client if none exists for the
        current thread.
        """
        key = threading.current_thread().name
        mc = self.pop(key, None)
        if mc is None:
            mc = self.master.clone()
        try:
            yield mc
        finally:
            self[key] = mc

# This makes sure ThreadMappedPool doesn't exist with non-thread Pythons.
try:
    import threading
except ImportError:
    del ThreadMappedPool

if __name__ == "__main__":
    import doctest
    doctest.testmod()