deps/uv/docs/src/handle.rst
.. _handle:
:c:type:`uv_handle_t` --- Base handle
=====================================
`uv_handle_t` is the base type for all libuv handle types.
Structures are aligned so that any libuv handle can be cast to `uv_handle_t`.
All API functions defined here work with any handle type.
Data types
----------
.. c:type:: uv_handle_t
The base libuv handle type.
.. c:type:: uv_any_handle
Union of all handle types.
.. c:type:: void (*uv_alloc_cb)(uv_handle_t* handle, size_t suggested_size, uv_buf_t* buf)
Type definition for callback passed to :c:func:`uv_read_start` and
:c:func:`uv_udp_recv_start`. The user must fill the supplied :c:type:`uv_buf_t`
structure with whatever size, as long as it's > 0. A suggested size (65536 at the moment)
is provided, but it doesn't need to be honored. Setting the buffer's length to 0
will trigger a ``UV_ENOBUFS`` error in the :c:type:`uv_udp_recv_cb` or
:c:type:`uv_read_cb` callback.
.. c:type:: void (*uv_close_cb)(uv_handle_t* handle)
Type definition for callback passed to :c:func:`uv_close`.
Public members
^^^^^^^^^^^^^^
.. c:member:: uv_loop_t* uv_handle_t.loop
Pointer to the :c:type:`uv_loop_t` where the handle is running on. Readonly.
.. c:member:: void* uv_handle_t.data
Space for user-defined arbitrary data. libuv does not use this field.
API
---
.. c:function:: int uv_is_active(const uv_handle_t* handle)
Returns non-zero if the handle is active, zero if it's inactive. What
"active" means depends on the type of handle:
- A uv_async_t handle is always active and cannot be deactivated, except
by closing it with uv_close().
- A uv_pipe_t, uv_tcp_t, uv_udp_t, etc. handle - basically any handle that
deals with i/o - is active when it is doing something that involves i/o,
like reading, writing, connecting, accepting new connections, etc.
- A uv_check_t, uv_idle_t, uv_timer_t, etc. handle is active when it has
been started with a call to uv_check_start(), uv_idle_start(), etc.
Rule of thumb: if a handle of type `uv_foo_t` has a `uv_foo_start()`
function, then it's active from the moment that function is called.
Likewise, `uv_foo_stop()` deactivates the handle again.
.. c:function:: int uv_is_closing(const uv_handle_t* handle)
Returns non-zero if the handle is closing or closed, zero otherwise.
.. note::
This function should only be used between the initialization of the handle and the
arrival of the close callback.
.. c:function:: void uv_close(uv_handle_t* handle, uv_close_cb close_cb)
Request handle to be closed. `close_cb` will be called asynchronously after
this call. This MUST be called on each handle before memory is released.
Handles that wrap file descriptors are closed immediately but
`close_cb` will still be deferred to the next iteration of the event loop.
It gives you a chance to free up any resources associated with the handle.
In-progress requests, like uv_connect_t or uv_write_t, are cancelled and
have their callbacks called asynchronously with status=UV_ECANCELED.
.. c:function:: void uv_ref(uv_handle_t* handle)
Reference the given handle. References are idempotent, that is, if a handle
is already referenced calling this function again will have no effect.
See :ref:`refcount`.
.. c:function:: void uv_unref(uv_handle_t* handle)
Un-reference the given handle. References are idempotent, that is, if a handle
is not referenced calling this function again will have no effect.
See :ref:`refcount`.
.. c:function:: int uv_has_ref(const uv_handle_t* handle)
Returns non-zero if the handle referenced, zero otherwise.
See :ref:`refcount`.
.. c:function:: size_t uv_handle_size(uv_handle_type type)
Returns the size of the given handle type. Useful for FFI binding writers
who don't want to know the structure layout.
Miscellaneous API functions
---------------------------
The following API functions take a :c:type:`uv_handle_t` argument but they work
just for some handle types.
.. c:function:: int uv_send_buffer_size(uv_handle_t* handle, int* value)
Gets or sets the size of the send buffer that the operating
system uses for the socket.
If `*value` == 0, it will return the current send buffer size,
otherwise it will use `*value` to set the new send buffer size.
This function works for TCP, pipe and UDP handles on Unix and for TCP and
UDP handles on Windows.
.. note::
Linux will set double the size and return double the size of the original set value.
.. c:function:: int uv_recv_buffer_size(uv_handle_t* handle, int* value)
Gets or sets the size of the receive buffer that the operating
system uses for the socket.
If `*value` == 0, it will return the current receive buffer size,
otherwise it will use `*value` to set the new receive buffer size.
This function works for TCP, pipe and UDP handles on Unix and for TCP and
UDP handles on Windows.
.. note::
Linux will set double the size and return double the size of the original set value.
.. c:function:: int uv_fileno(const uv_handle_t* handle, uv_os_fd_t* fd)
Gets the platform dependent file descriptor equivalent.
The following handles are supported: TCP, pipes, TTY, UDP and poll. Passing
any other handle type will fail with `UV_EINVAL`.
If a handle doesn't have an attached file descriptor yet or the handle
itself has been closed, this function will return `UV_EBADF`.
.. warning::
Be very careful when using this function. libuv assumes it's in control of the file
descriptor so any change to it may lead to malfunction.
.. _refcount:
Reference counting
------------------
The libuv event loop (if run in the default mode) will run until there are no
active `and` referenced handles left. The user can force the loop to exit early
by unreferencing handles which are active, for example by calling :c:func:`uv_unref`
after calling :c:func:`uv_timer_start`.
A handle can be referenced or unreferenced, the refcounting scheme doesn't use
a counter, so both operations are idempotent.
All handles are referenced when active by default, see :c:func:`uv_is_active`
for a more detailed explanation on what being `active` involves.