System.ZMQ

0MQ haskell binding. The API closely follows the C-API of 0MQ with the main difference that sockets are typed. The documentation of the individual socket types and socket options is copied from 0MQ's man pages authored by Martin Sustrik.

Documentation

type Size = Word

data Context

A 0MQ context representation.

data Socket a

A 0MQ Socket.

data Flag

Flags to apply on send operations (cf. man zmq_send)

NoBlock

Send operation should be performed in non-blocking mode. If it cannot be performed immediatley an error will be thrown (errno is set to EAGAIN).

NoFlush

send should not flush the message downstream immediately, instead it should batch messages send with NoFlush and really send them only when flush is invoked. zmq_send(3) states: "This is an optimisation for cases where several messages are sent in a single business transaction. However, the effect is measurable only in extremely high-perf scenarios (million messages a second or so). If that's not your case, use standard flushing send instead."

Constructors

NoBlock

ZMQ_NOBLOCK

NoFlush

ZMQ_NOFLUSH

Instances

Eq Flag

Ord Flag

Show Flag

data SocketOption

The option to set on 0MQ sockets (descriptions reproduced here from zmq_setsockopt(3) (cf. man zmq_setsockopt for further details)).

HighWM

High watermark for the message pipes associated with the socket. The water mark cannot be exceeded. If the messages don't fit into the pipe emergency mechanisms of the particular socket type are used (block, drop etc.) If HWM is set to zero, there are no limits for the content of the pipe. Default: 0

LowWM

Low watermark makes sense only if high watermark is defined (i.e. is non-zero). When the emergency state is reached when messages overflow the pipe, the emergency lasts at most till the size of the pipe decreases to low watermark. Normal state is resumed at that point. Default: 0

Swap

Swap allows the pipe to exceed high watermark. However, the data are written to the disk rather than held in the memory. Until high watermark is exceeded there is no disk activity involved though. The value of the option defines maximal size of the swap file. Default: 0

Affinity

Affinity defines which threads in the thread pool will be used to handle newly created sockets. This way you can dedicate some of the threads (CPUs) to a specific work. Value of 0 means no affinity. Work is distributed fairly among the threads in the thread pool. For non-zero values, the lowest bit corresponds to the thread 1, second lowest bit to the thread 2 etc. Thus, value of 3 means that from now on newly created sockets will handle I/O activity exclusively using threads no. 1 and 2. Default: 0

Identity

Identity of the socket. Identity is important when restarting applications. If the socket has no identity, each run of the application is completely separated from other runs. However, with identity application reconnects to existing infrastructure left by the previous run. Thus it may receive messages that were sent in the meantime, it shares pipe limits with the previous run etc. Default: NULL

Rate

This option applies only to sending side of multicast transports (pgm & udp). It specifies maximal outgoing data rate that an individual sender socket can send. Default: 100

RecoveryIVL

This option applies only to multicast transports (pgm & udp). It specifies how long can the receiver socket survive when the sender is inaccessible. Keep in mind that large recovery intervals at high data rates result in very large recovery buffers, meaning that you can easily overload your box by setting say 1 minute recovery interval at 1Gb/s rate (requires 7GB in-memory buffer). Default: 10

McastLoop

This option applies only to multicast transports (pgm & udp). Value of 1 means that the mutlicast packets can be received on the box they were sent from. Setting the value to 0 disables the loopback functionality which can have negative impact on the performance. If possible, disable the loopback in production environments. Default: 1

SendBuf

Sets the underlying kernel transmit buffer size to the specified size. See SO_SNDBUF POSIX socket option. Value of zero means leaving the OS default unchanged. Default: 0

ReceiveBuf

Sets the underlying kernel receive buffer size to the specified size. See SO_RCVBUF POSIX socket option. Value of zero means leaving the OS default unchanged. Default: 0

Constructors

HighWM Int64

ZMQ_HWM

LowWM Int64

ZMQ_LWM

Swap Int64

ZMQ_SWAP

Affinity Int64

ZMQ_AFFINITY

Identity String

ZMQ_IDENTITY

Rate Word64

ZMQ_RATE

RecoveryIVL Word64

ZMQ_RECOVERY_IVL

McastLoop Word64

ZMQ_MCAST_LOOP

SendBuf Word64

ZMQ_SNDBUF

ReceiveBuf Word64

ZMQ_RCVBUF

Instances

Eq SocketOption

Ord SocketOption

Show SocketOption

data Poll

Type representing a descriptor, poll is waiting for (either a 0MQ socket or a file descriptor) plus the type of event of wait for.

Constructors

forall a . S (Socket a) PollEvent

F Fd PollEvent

data PollEvent

The events to wait for in poll (cf. man zmq_poll)

Constructors

In

ZMQ_POLLIN (incoming messages)

Out

ZMQ_POLLOUT (outgoing messages, i.e. at least 1 byte can be written)

InOut

ZMQ_POLLIN | ZMQ_POLLOUT

Instances

Eq PollEvent

Ord PollEvent

Show PollEvent

data P2P

Socket to communicate with a single peer. Allows for only a single connect or a single bind. There's no message routing or message filtering involved. Compatible peer sockets: P2P.

Constructors

P2P

Instances

SType P2P

data Pub

Socket to distribute data. receive function is not implemented for this socket type. Messages are distributed in fanout fashion to all the peers. Compatible peer sockets: Sub.

Constructors

Pub

Instances

SType Pub

data Sub

Socket to subscribe for data. Send function is not implemented for this socket type. Initially, socket is subscribed for no messages. Use subscribe to specify which messages to subscribe for. Compatible peer sockets: Pub.

Constructors

Sub

Instances

SubsType Sub

SType Sub

data Req

Socket to send requests and receive replies. Requests are load-balanced among all the peers. This socket type allows only an alternated sequence of send's and recv's. Compatible peer sockets: Rep, Xrep.

Constructors

Req

Instances

SType Req

data Rep

Socket to receive requests and send replies. This socket type allows only an alternated sequence of receive's and send's. Each send is routed to the peer that issued the last received request. Compatible peer sockets: Req, XReq.

Constructors

Rep

Instances

SType Rep

data XReq

Special socket type to be used in request/reply middleboxes such as zmq_queue(7). Requests forwarded using this socket type should be tagged by a proper prefix identifying the original requester. Replies received by this socket are tagged with a proper postfix that can be use to route the reply back to the original requester. Compatible peer sockets: Rep, Xrep.

Constructors

Xreq

Instances

SType XReq

data XRep

Special socket type to be used in request/reply middleboxes such as zmq_queue(7). Requests received using this socket are already properly tagged with prefix identifying the original requester. When sending a reply via XREP socket the message should be tagged with a prefix from a corresponding request. Compatible peer sockets: Req, Xreq.

Constructors

Xrep

Instances

SType XRep

data Up

Socket to receive messages from up the stream. Messages are fair-queued from among all the connected peers. Send function is not implemented for this socket type. Compatible peer sockets: Down.

Constructors

Up

Instances

SType Up

data Down

Socket to send messages down stream. Messages are load-balanced among all the connected peers. Send function is not implemented for this socket type. Compatible peer sockets: Up.

Constructors

Down

Instances

SType Down

init :: Size -> Size -> Bool -> IO Context

Initialize a 0MQ context (cf. zmq_init for details).

term :: Context -> IO ()

Terminate 0MQ context (cf. zmq_term).

socket :: SType a => Context -> a -> IO (Socket a)

Create a new 0MQ socket within the given context.

close :: Socket a -> IO ()

Close a 0MQ socket.

setOption :: Socket a -> SocketOption -> IO ()

Set the given option on the socket. Please note that there are certain combatibility constraints w.r.t the socket type (cf. man zmq_setsockopt).

Please note that subscribe/unsubscribe is handled with separate functions.

subscribe :: SubsType a => Socket a -> String -> IO ()

Subscribe Socket to given subscription.

unsubscribe :: SubsType a => Socket a -> String -> IO ()

Unsubscribe Socket from given subscription.

bind :: Socket a -> String -> IO ()

Bind the socket to the given address (zmq_bind)

connect :: Socket a -> String -> IO ()

Connect the socket to the given address (zmq_connect).

send :: Socket a -> ByteString -> [Flag] -> IO ()

Send the given ByteString over the socket (zmq_send).

flush :: Socket a -> IO ()

Flush the given socket (useful for sends with NoFlush).

receive :: Socket a -> [Flag] -> IO ByteString

Receive a ByteString from socket (zmq_recv).

poll :: [Poll] -> Timeout -> IO [Poll]

Polls for events on the given Poll descriptors. Returns the list of Poll descriptors for which an event occured (cf. zmq_poll).