Package org.zeromq

Class ZMQ

java.lang.Object
org.zeromq.ZMQ

public class ZMQ extends Object

The ØMQ lightweight messaging kernel is a library which extends the standard socket interfaces with features traditionally provided by specialised messaging middleware products. ØMQ sockets provide an abstraction of asynchronous message queues, multiple messaging patterns, message filtering (subscriptions), seamless access to multiple transport protocols and more.

Following is an overview of ØMQ concepts, describes how ØMQ abstracts standard sockets and provides a reference manual for the functions provided by the ØMQ library.

Contexts

Before using any ØMQ library functions you must create a ØMQ context using context(int). When you exit your application you must destroy the context using ZMQ.Context.close().

Thread safety

A ØMQ context is thread safe and may be shared among as many application threads as necessary, without any additional locking required on the part of the caller.
Individual ØMQ sockets are not thread safe except in the case where full memory barriers are issued when migrating a socket from one thread to another.
In practice this means applications can create a socket in one thread with * ZMQ.Context.socket(SocketType) and then pass it to a newly created thread as part of thread initialization.

Multiple contexts

Multiple contexts may coexist within a single application.
Thus, an application can use ØMQ directly and at the same time make use of any number of additional libraries or components which themselves make use of ØMQ as long as the above guidelines regarding thread safety are adhered to.

Messages

A ØMQ message is a discrete unit of data passed between applications or components of the same application. ØMQ messages have no internal structure and from the point of view of ØMQ itself they are considered to be opaque binary data.

Sockets

ØMQ sockets present an abstraction of a asynchronous message queue, with the exact queueing semantics depending on the socket type in use.

Transports

A ØMQ socket can use multiple different underlying transport mechanisms. Each transport mechanism is suited to a particular purpose and has its own advantages and drawbacks.

The following transport mechanisms are provided:

  • Unicast transport using TCP
  • Local inter-process communication transport
  • Local in-process (inter-thread) communication transport

Proxies

ØMQ provides proxies to create fanout and fan-in topologies. A proxy connects a frontend socket to a backend socket and switches all messages between the two sockets, opaquely. A proxy may optionally capture all traffic to a third socket.

Security

A ØMQ socket can select a security mechanism. Both peers must use the same security mechanism.

The following security mechanisms are provided for IPC and TCP connections:

  • Null security
  • Plain-text authentication using username and password
  • Elliptic curve authentication and encryption
  • Field Details

    • SNDMORE

      public static final int SNDMORE
      Socket flag to indicate that more message parts are coming.
      See Also:
    • DONTWAIT

      public static final int DONTWAIT
      Socket flag to indicate a nonblocking send or recv mode.
      See Also:
    • NOBLOCK

      public static final int NOBLOCK
      See Also:
    • PAIR

      @Deprecated public static final int PAIR
      Deprecated.
      See Also:
    • PUB

      @Deprecated public static final int PUB
      Deprecated.
      See Also:
    • SUB

      @Deprecated public static final int SUB
      Deprecated.
      See Also:
    • REQ

      @Deprecated public static final int REQ
      Deprecated.
      See Also:
    • REP

      @Deprecated public static final int REP
      Deprecated.
      See Also:
    • DEALER

      @Deprecated public static final int DEALER
      Deprecated.
      See Also:
    • XREQ

      @Deprecated public static final int XREQ
      Deprecated.
      As of release 3.0 of zeromq, replaced by DEALER
      Old alias for DEALER flag. Flag to specify a XREQ socket, receiving side must be a XREP.
      See Also:
    • ROUTER

      @Deprecated public static final int ROUTER
      Deprecated.
      See Also:
    • XREP

      @Deprecated public static final int XREP
      Deprecated.
      As of release 3.0 of zeromq, replaced by ROUTER
      Old alias for ROUTER flag. Flag to specify the receiving part of a XREQ socket.
      See Also:
    • PULL

      @Deprecated public static final int PULL
      Deprecated.
      See Also:
    • PUSH

      @Deprecated public static final int PUSH
      Deprecated.
      See Also:
    • XPUB

      @Deprecated public static final int XPUB
      Deprecated.
      See Also:
    • XSUB

      @Deprecated public static final int XSUB
      Deprecated.
      See Also:
    • STREAM

      @Deprecated public static final int STREAM
      Deprecated.
      See Also:
    • STREAMER

      @Deprecated public static final int STREAMER
      Deprecated.
      Flag to specify a STREAMER device.
      See Also:
    • FORWARDER

      @Deprecated public static final int FORWARDER
      Deprecated.
      Flag to specify a FORWARDER device.
      See Also:
    • QUEUE

      @Deprecated public static final int QUEUE
      Deprecated.
      Flag to specify a QUEUE device.
      See Also:
    • UPSTREAM

      @Deprecated public static final int UPSTREAM
      Deprecated.
      See Also:
    • DOWNSTREAM

      @Deprecated public static final int DOWNSTREAM
      Deprecated.
      See Also:
    • EVENT_CONNECTED

      public static final int EVENT_CONNECTED
      EVENT_CONNECTED: connection established. The EVENT_CONNECTED event triggers when a connection has been established to a remote peer. This can happen either synchronous or asynchronous. Value is the FD of the newly connected socket.
      See Also:
    • EVENT_CONNECT_DELAYED

      public static final int EVENT_CONNECT_DELAYED
      EVENT_CONNECT_DELAYED: synchronous connect failed, it's being polled. The EVENT_CONNECT_DELAYED event triggers when an immediate connection attempt is delayed and its completion is being polled for. Value has no meaning.
      See Also:
    • EVENT_DELAYED

      @Deprecated public static final int EVENT_DELAYED
      Deprecated.
      See Also:
    • EVENT_CONNECT_RETRIED

      public static final int EVENT_CONNECT_RETRIED
      EVENT_CONNECT_RETRIED: asynchronous connect / reconnection attempt. The EVENT_CONNECT_RETRIED event triggers when a connection attempt is being handled by reconnect timer. The reconnect interval's recomputed for each attempt. Value is the reconnect interval.
      See Also:
    • EVENT_RETRIED

      @Deprecated public static final int EVENT_RETRIED
      Deprecated.
      See Also:
    • EVENT_LISTENING

      public static final int EVENT_LISTENING
      EVENT_LISTENING: socket bound to an address, ready to accept connections. The EVENT_LISTENING event triggers when a socket's successfully bound to a an interface. Value is the FD of the newly bound socket.
      See Also:
    • EVENT_BIND_FAILED

      public static final int EVENT_BIND_FAILED
      EVENT_BIND_FAILED: socket could not bind to an address. The EVENT_BIND_FAILED event triggers when a socket could not bind to a given interface. Value is the errno generated by the bind call.
      See Also:
    • EVENT_ACCEPTED

      public static final int EVENT_ACCEPTED
      EVENT_ACCEPTED: connection accepted to bound interface. The EVENT_ACCEPTED event triggers when a connection from a remote peer has been established with a socket's listen address. Value is the FD of the accepted socket.
      See Also:
    • EVENT_ACCEPT_FAILED

      public static final int EVENT_ACCEPT_FAILED
      EVENT_ACCEPT_FAILED: could not accept client connection. The EVENT_ACCEPT_FAILED event triggers when a connection attempt to a socket's bound address fails. Value is the errno generated by accept.
      See Also:
    • EVENT_CLOSED

      public static final int EVENT_CLOSED
      EVENT_CLOSED: connection closed. The EVENT_CLOSED event triggers when a connection's underlying descriptor has been closed. Value is the former FD of the for the closed socket. FD has been closed already!
      See Also:
    • EVENT_CLOSE_FAILED

      public static final int EVENT_CLOSE_FAILED
      EVENT_CLOSE_FAILED: connection couldn't be closed. The EVENT_CLOSE_FAILED event triggers when a descriptor could not be released back to the OS. Implementation note: ONLY FOR IPC SOCKETS. Value is the errno generated by unlink.
      See Also:
    • EVENT_DISCONNECTED

      public static final int EVENT_DISCONNECTED
      EVENT_DISCONNECTED: broken session. The EVENT_DISCONNECTED event triggers when the stream engine (tcp and ipc specific) detects a corrupted / broken session. Value is the FD of the socket.
      See Also:
    • EVENT_MONITOR_STOPPED

      public static final int EVENT_MONITOR_STOPPED
      EVENT_MONITOR_STOPPED: monitor has been stopped. The EVENT_MONITOR_STOPPED event triggers when the monitor for a socket is stopped.
      See Also:
    • EVENT_HANDSHAKE_PROTOCOL

      public static final int EVENT_HANDSHAKE_PROTOCOL
      EVENT_HANDSHAKE_PROTOCOL: protocol has been successfully negotiated. The EVENT_HANDSHAKE_PROTOCOL event triggers when the stream engine (tcp and ipc) successfully negotiated a protocol version with the peer. Value is the version number (0 for unversioned, 3 for V3).
      See Also:
    • EVENT_ALL

      public static final int EVENT_ALL
      EVENT_ALL: all events known. The EVENT_ALL constant can be used to set up a monitor for all known events.
      See Also:
    • MESSAGE_SEPARATOR

      public static final byte[] MESSAGE_SEPARATOR
    • SUBSCRIPTION_ALL

      public static final byte[] SUBSCRIPTION_ALL
    • PROXY_PAUSE

      public static final byte[] PROXY_PAUSE
    • PROXY_RESUME

      public static final byte[] PROXY_RESUME
    • PROXY_TERMINATE

      public static final byte[] PROXY_TERMINATE
    • CHARSET

      public static final Charset CHARSET
  • Constructor Details

    • ZMQ

      private ZMQ()
  • Method Details

    • context

      public static ZMQ.Context context(int ioThreads)
      Create a new Context.
      Parameters:
      ioThreads - Number of threads to use, usually 1 is sufficient for most use cases.
      Returns:
      the Context
    • device

      @Deprecated public static boolean device(int type, ZMQ.Socket frontend, ZMQ.Socket backend)
      Deprecated.
    • proxy

      public static boolean proxy(ZMQ.Socket frontend, ZMQ.Socket backend, ZMQ.Socket capture)
      Starts the built-in 0MQ proxy in the current application thread. The proxy connects a frontend socket to a backend socket. Conceptually, data flows from frontend to backend. Depending on the socket types, replies may flow in the opposite direction. The direction is conceptual only; the proxy is fully symmetric and there is no technical difference between frontend and backend.

      Before calling ZMQ.proxy() you must set any socket options, and connect or bind both frontend and backend sockets. The two conventional proxy models are:

      ZMQ.proxy() runs in the current thread and returns only if/when the current context is closed.

      Parameters:
      frontend - ZMQ.Socket
      backend - ZMQ.Socket
      capture - If the capture socket is not NULL, the proxy shall send all messages, received on both frontend and backend, to the capture socket. The capture socket should be a ZMQ_PUB, ZMQ_DEALER, ZMQ_PUSH, or ZMQ_PAIR socket.
    • proxy

      public static boolean proxy(ZMQ.Socket frontend, ZMQ.Socket backend, ZMQ.Socket capture, ZMQ.Socket control)
    • poll

      public static int poll(Selector selector, ZMQ.PollItem[] items, long timeout)
    • poll

      public static int poll(Selector selector, ZMQ.PollItem[] items, int count, long timeout)
    • getMajorVersion

      public static int getMajorVersion()
      Returns:
      Major version number of the ZMQ library.
    • getMinorVersion

      public static int getMinorVersion()
      Returns:
      Major version number of the ZMQ library.
    • getPatchVersion

      public static int getPatchVersion()
      Returns:
      Major version number of the ZMQ library.
    • getFullVersion

      public static int getFullVersion()
      Returns:
      Full version number of the ZMQ library used for comparing versions.
    • makeVersion

      public static int makeVersion(int major, int minor, int patch)
      Parameters:
      major - Version major component.
      minor - Version minor component.
      patch - Version patch component.
      Returns:
      Comparible single int version number.
    • getVersionString

      public static String getVersionString()
      Returns:
      String version number in the form major.minor.patch.
    • msleep

      public static void msleep(long millis)
    • sleep

      public static void sleep(long seconds)
    • sleep

      public static void sleep(long amount, TimeUnit unit)