Dreadlock is a simple + fast network-locking daemon. A client can connect to dreadlock over TCP and ensure exclusive access to a particular resource.
Note: due to network partitions and things of that nature, this is only a SOFT guarantee of exclusivity; don't use this program for banking. It is optimized for speedy locking, not safe locking. Something like zookeeper is better for safe locking.
It talks over TCP and supports two commands. First, lock:
lock <key> <timeout>\r\n
Issuing lock will block the calling client for timeout
milliseconds until either the key is held exclusively by
this client or the timeout elapses. Keys must contain only
ascii letters and digits.
The response will be either:
l locked\r\n
or
t timeout\r\n
Your client should raise an exception on t timeout (or
return an error code, depending on language). Note:
timeouts are +/- 100ms, so don't count on deadly accuracy.
Clients will be given the lock as it is released in first-come-first-serve order. If a client's TCP connection to dreadlock drops, it is considered dead, and all locks it holds are immediately released.
To explicitly release a lock when a client is done, use:
unlock <key>\r\n
The response will be:
u unlocked\r\n
A few errors are possible, like unlocking a lock you do not hold, re-locking a lock you already hold, etc. Errors are always of the format:
e error message\r\n
Your client should raise an exception and provide the error message
as a descriptive string for the error.
A protocol syntax error will cause the connection to be rudely dropped on your client (and dreadlock will print a warning to stderr).
To build dreadlock, you need Russ Cox's libtask library
installed. For running high concurrency dreadlock servers
on linux, it's recommended to use
this fork which supports
epoll() on linux. The standard libtask has a fixed limit
of 1024 sockets; the epoll()-enabled fork has no arbitrary
limits (other than ulimit).
make and make install will do it; make all will attempt
to use ragel to rebuild the parsing state machine C file,
but you must have a recent version of ragel installed on
your system to do so.
Just run dreadlock and it will listen on port 6001. Optionally,
if you specify a command line argument, it will listen on that port
instead:
dreadlock
or
dreadlock 11066
Consider dreadlock beta software for now.
Jamie Turner jamie@bu.mp