zmq_ipc - 0MQ local inter-process communication transport


The inter-process transport passes messages between local processes using a system-dependent IPC mechanism.

The inter-process transport is currently only implemented on operating systems that provide UNIX domain sockets.


A 0MQ endpoint is a string consisting of a 'transport'`://` followed by an 'address'. The 'transport' specifies the underlying protocol to use. The 'address' specifies the transport-specific address to connect to.

For the inter-process transport, the transport is ipc, and the meaning of the 'address' part is defined below.

Binding a socket

When binding a 'socket' to a local address using zmq_bind() with the 'ipc' transport, the 'endpoint' shall be interpreted as an arbitrary string identifying the 'pathname' to create. The 'pathname' must be unique within the operating system namespace used by the 'ipc' implementation, and must fulfill any restrictions placed by the operating system on the format and length of a 'pathname'.

When the address is wild-card *, zmq_bind() shall generate a unique temporary pathname. The caller should retrieve this pathname using the ZMQ_LAST_ENDPOINT socket option. See zmq_getsockopt for details.

any existing binding to the same endpoint shall be overridden. That is, if a second process binds to an endpoint already bound by a process, this will succeed and the first process will lose its binding. In this behaviour, the 'ipc' transport is not consistent with the 'tcp' or 'inproc' transports.
the endpoint pathname must be writable by the process. When the endpoint starts with '/', e.g., ipc:///pathname, this will be an absolute pathname. If the endpoint specifies a directory that does not exist, the bind shall fail.
on Linux only, when the endpoint pathname starts with @, the abstract namespace shall be used. The abstract namespace is independent of the filesystem and if a process attempts to bind an endpoint already bound by a process, it will fail. See unix(7) for details.
IPC pathnames have a maximum size that depends on the operating system. On Linux, the maximum is 113 characters including the "ipc://" prefix (107 characters for the real path name).

Unbinding wild-card address from a socket

When wild-card * 'endpoint' was used in zmq_bind(), the caller should use real 'endpoint' obtained from the ZMQ_LAST_ENDPOINT socket option to unbind this 'endpoint' from a socket using zmq_unbind().

Connecting a socket

When connecting a 'socket' to a peer address using zmq_connect() with the 'ipc' transport, the 'endpoint' shall be interpreted as an arbitrary string identifying the 'pathname' to connect to. The 'pathname' must have been previously created within the operating system namespace by assigning it to a 'socket' with zmq_bind().


Assigning a local address to a socket
//  Assign the pathname "/tmp/feeds/0"
rc = zmq_bind(socket, "ipc:///tmp/feeds/0");
assert (rc == 0);
Connecting a socket
//  Connect to the pathname "/tmp/feeds/0"
rc = zmq_connect(socket, "ipc:///tmp/feeds/0");
assert (rc == 0);



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