Eventfd

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[[Linux_APIs|Linux]] offers the eventfd abstraction for file descriptor-based userspace notification. It is backed by ~~merely~~ a single <tt>uint64_t</tt> in the kernel, unlike a pipe (which is usually backed by a much larger buffer). It is thus the most lightweight method of IPC available to userspace. The maximum value of the eventfd counter is 2^64-2 (0xfffffffffffffffe), and the minimum (and default) value is 0.

[[Linux_APIs|Linux]] offers the eventfd abstraction for file descriptor-based userspace notification. It is backed by a single <tt>uint64_t</tt> in the kernel, unlike a pipe (which is usually backed by a much larger buffer). It is thus the most lightweight method of IPC available to userspace. The maximum value of the eventfd counter is 2^64-2 (0xfffffffffffffffe), and the minimum (and default) value is 0.

In the past, a full pipe was often used to interrupt a thread that was blocking in <tt>poll(2)</tt> (or <tt>select</tt>, or <tt>[[epoll]]</tt>, etc.). An eventfd can serve this same purpose while requiring less kernel memory.

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<tt>POLLOUT</tt> is high whenever the value of the eventfd is less than its maximum, i.e. 0xfffffffffffffffd or less. It only guarantees that a value of 1 can be written without blocking.

==External links==

* [https://man7.org/linux/man-pages/man2/eventfd.2.html eventfd(2)] man page

Eventfd: Difference between revisions

Dank (talk | contribs)

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-[[Linux_APIs|Linux]] offers the eventfd abstraction for file descriptor-based userspace notification. It is backed by merely a single <tt>uint64_t</tt> in the kernel, unlike a pipe (which is usually backed by a much larger buffer). It is thus the most lightweight method of IPC available to userspace. The maximum value of the eventfd counter is 2^64-2 (0xfffffffffffffffe), and the minimum (and default) value is 0.
+[[Linux_APIs|Linux]] offers the eventfd abstraction for file descriptor-based userspace notification. It is backed by a single <tt>uint64_t</tt> in the kernel, unlike a pipe (which is usually backed by a much larger buffer). It is thus the most lightweight method of IPC available to userspace. The maximum value of the eventfd counter is 2^64-2 (0xfffffffffffffffe), and the minimum (and default) value is 0.
 In the past, a full pipe was often used to interrupt a thread that was blocking in <tt>poll(2)</tt> (or <tt>select</tt>, or <tt>[[epoll]]</tt>, etc.). An eventfd can serve this same purpose while requiring less kernel memory.
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 <tt>POLLOUT</tt> is high whenever the value of the eventfd is less than its maximum, i.e. 0xfffffffffffffffd or less. It only guarantees that a value of 1 can be written without blocking.
+==External links==
+* [https://man7.org/linux/man-pages/man2/eventfd.2.html eventfd(2)] man page