EPOLL(7) Standards, Environments, and Macros EPOLL(7)

epoll - Linux-compatible I/O event notification facility

#include <sys/epoll.h>

epoll is a facility for efficient event-oriented I/O that has a similar model to poll(2), but does not necessitate rescanning a set of file descriptors to wait for an event. epoll is of Linux origins, and this facility is designed to be binary-compatible with the Linux facility, including the following interfaces:

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epoll_create(3C) creates an epoll instance, returning a file descriptor. It contains a size argument which is meaningful only in as much as it cannot be 0.
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epoll_create1(3C) also creates an epoll instance, but eliminates the meaningless size argument -- replacing it instead with a flags argument.
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epoll_ctl(3C) allows file descriptors to be added (via EPOLL_CTL_ADD), deleted (via EPOLL_CTL_DEL) or modified (via EPOLL_CTL_MOD) with respect to the epoll'd set of file descriptors.
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epoll_wait(3C) fetches pending events for file descriptors added via epoll_ctl(3C), blocking the caller if no such events are pending.
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epoll_pwait(3C) operates in a similar manner to epoll_wait(3C), but allows the caller to specify a signal mask to be set atomically with respect to waiting for events.

The epoll facility is implemented for purposes of offering compatibility to and portability of Linux-borne applications; native applications should continue to prefer using event ports via the port_create(3C), port_associate(3C) and port_getn(3C) interfaces. In particular, use of epoll in a multithreaded environment is fraught with peril; even when using EPOLLONESHOT for one-shot events, there are race conditions with respect to close(2) that are unresolvable. (For more details, see the aborted effort in Linux to resolve this via the proposed EPOLL_CTL_DISABLE operation.) The event port facility -- like the BSD kqueue facility that inspired it -- is designed to deal with such issues via explicit event source dissociation.

While a best effort has been made to mimic the Linux semantics, there are some semantics that are too peculiar or ill-conceived to merit accommodation. In particular, the Linux epoll facility will -- by design -- continue to generate events for closed file descriptors where/when the underlying file description remains open. For example, if one were to fork(2) and subsequently close an actively epoll'd file descriptor in the parent, any events generated in the child on the implicitly duplicated file descriptor will continue to be delivered to the parent -- despite the fact that the parent itself no longer has any notion of the file description! This epoll facility refuses to honor these semantics; closing the EPOLL_CTL_ADD'd file descriptor will always result in no further events being generated for that event description.

epoll_create(3C), epoll_create1(3C), epoll_ctl(3C), epoll_pwait(3C), epoll_wait(3C), port_associate(3C), port_create(3C), port_dissociate(3C), port_get(3C), pselect(3C)
May 16, 2020 OmniOS