Why can I use standard I/O multiplexing functions such as select() or poll() on ØMQ sockets?
ØMQ socket is not a standard POSIX socket. It would be great if it was, however, POSIX doesn’t provide a mechanism to simulate file descriptors in user space. To convert ØMQ sockets into POSIX file descriptors we would have either to move ØMQ to kernel-space or hack the kernel to provide the functionality needed. In both cases we would have to sacrifice portability and stick to a single operating system. Note that there’s a way to retrieve a file descriptor from ØMQ socket (ZMQ_FD socket option) that you can poll on from version 2.1 onwards, however, there are some serious caveats when using it. Check the documentation carefully before using this feature.
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