forked from cory/tildefriends
Cory McWilliams
da51e87774
git-svn-id: https://www.unprompted.com/svn/projects/tildefriends/trunk@3650 ed5197a5-7fde-0310-b194-c3ffbd925b24
149 lines
5.5 KiB
ReStructuredText
149 lines
5.5 KiB
ReStructuredText
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.. _poll:
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:c:type:`uv_poll_t` --- Poll handle
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===================================
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Poll handles are used to watch file descriptors for readability,
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writability and disconnection similar to the purpose of :man:`poll(2)`.
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The purpose of poll handles is to enable integrating external libraries that
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rely on the event loop to signal it about the socket status changes, like
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c-ares or libssh2. Using uv_poll_t for any other purpose is not recommended;
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:c:type:`uv_tcp_t`, :c:type:`uv_udp_t`, etc. provide an implementation that is faster and
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more scalable than what can be achieved with :c:type:`uv_poll_t`, especially on
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Windows.
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It is possible that poll handles occasionally signal that a file descriptor is
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readable or writable even when it isn't. The user should therefore always
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be prepared to handle EAGAIN or equivalent when it attempts to read from or
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write to the fd.
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It is not okay to have multiple active poll handles for the same socket, this
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can cause libuv to busyloop or otherwise malfunction.
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The user should not close a file descriptor while it is being polled by an
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active poll handle. This can cause the handle to report an error,
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but it might also start polling another socket. However the fd can be safely
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closed immediately after a call to :c:func:`uv_poll_stop` or :c:func:`uv_close`.
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.. note::
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On windows only sockets can be polled with poll handles. On Unix any file
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descriptor that would be accepted by :man:`poll(2)` can be used.
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.. note::
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On AIX, watching for disconnection is not supported.
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Data types
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----------
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.. c:type:: uv_poll_t
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Poll handle type.
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.. c:type:: void (*uv_poll_cb)(uv_poll_t* handle, int status, int events)
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Type definition for callback passed to :c:func:`uv_poll_start`.
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.. c:type:: uv_poll_event
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Poll event types
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::
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enum uv_poll_event {
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UV_READABLE = 1,
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UV_WRITABLE = 2,
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UV_DISCONNECT = 4,
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UV_PRIORITIZED = 8
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};
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Public members
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^^^^^^^^^^^^^^
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N/A
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.. seealso:: The :c:type:`uv_handle_t` members also apply.
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API
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---
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.. c:function:: int uv_poll_init(uv_loop_t* loop, uv_poll_t* handle, int fd)
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Initialize the handle using a file descriptor.
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.. versionchanged:: 1.2.2 the file descriptor is set to non-blocking mode.
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.. c:function:: int uv_poll_init_socket(uv_loop_t* loop, uv_poll_t* handle, uv_os_sock_t socket)
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Initialize the handle using a socket descriptor. On Unix this is identical
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to :c:func:`uv_poll_init`. On windows it takes a SOCKET handle.
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.. versionchanged:: 1.2.2 the socket is set to non-blocking mode.
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.. c:function:: int uv_poll_start(uv_poll_t* handle, int events, uv_poll_cb cb)
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Starts polling the file descriptor. `events` is a bitmask made up of
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`UV_READABLE`, `UV_WRITABLE`, `UV_PRIORITIZED` and `UV_DISCONNECT`. As soon
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as an event is detected the callback will be called with `status` set to 0,
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and the detected events set on the `events` field.
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The `UV_PRIORITIZED` event is used to watch for sysfs interrupts or TCP
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out-of-band messages.
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The `UV_DISCONNECT` event is optional in the sense that it may not be
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reported and the user is free to ignore it, but it can help optimize the
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shutdown path because an extra read or write call might be avoided.
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If an error happens while polling, `status` will be < 0 and corresponds
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with one of the `UV_E*` error codes (see :ref:`errors`). The user should
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not close the socket while the handle is active. If the user does that
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anyway, the callback *may* be called reporting an error status, but this is
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**not** guaranteed.
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.. note::
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Calling :c:func:`uv_poll_start` on a handle that is already active is
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fine. Doing so will update the events mask that is being watched for.
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.. note::
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Though `UV_DISCONNECT` can be set, it is unsupported on AIX and as such
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will not be set on the `events` field in the callback.
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.. note::
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If one of the events `UV_READABLE` or `UV_WRITABLE` are set, the
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callback will be called again, as long as the given fd/socket remains
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readable or writable accordingly. Particularly in each of the following
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scenarios:
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* The callback has been called because the socket became
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readable/writable and the callback did not conduct a read/write on
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this socket at all.
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* The callback committed a read on the socket, and has not read all the
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available data (when `UV_READABLE` is set).
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* The callback committed a write on the socket, but it remained
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writable afterwards (when `UV_WRITABLE` is set).
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* The socket has already became readable/writable before calling
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:c:func:`uv_poll_start` on a poll handle associated with this socket,
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and since then the state of the socket did not changed.
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In all of the above listed scenarios, the socket remains readable or
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writable and hence the callback will be called again (depending on the
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events set in the bitmask). This behaviour is known as level
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triggering.
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.. versionchanged:: 1.9.0 Added the `UV_DISCONNECT` event.
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.. versionchanged:: 1.14.0 Added the `UV_PRIORITIZED` event.
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.. c:function:: int uv_poll_stop(uv_poll_t* poll)
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Stop polling the file descriptor, the callback will no longer be called.
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.. note::
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Calling :c:func:`uv_poll_stop` is effective immediately: any pending
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callback is also canceled, even if the socket state change notification
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was already pending.
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.. seealso:: The :c:type:`uv_handle_t` API functions also apply.
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