.. _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.