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

uv_handle_t

The base libuv handle type.

uv_handle_type

The kind of the libuv handle.

typedef enum {
  UV_UNKNOWN_HANDLE = 0,
  UV_ASYNC,
  UV_CHECK,
  UV_FS_EVENT,
  UV_FS_POLL,
  UV_HANDLE,
  UV_IDLE,
  UV_NAMED_PIPE,
  UV_POLL,
  UV_PREPARE,
  UV_PROCESS,
  UV_STREAM,
  UV_TCP,
  UV_TIMER,
  UV_TTY,
  UV_UDP,
  UV_SIGNAL,
  UV_FILE,
  UV_HANDLE_TYPE_MAX
} uv_handle_type;
uv_any_handle

Union of all handle types.

void (*uv_alloc_cb)(uv_handle_t* handle, size_t suggested_size, uv_buf_t* buf)

Type definition for callback passed to uv_read_start() and uv_udp_recv_start(). The user must allocate memory and fill the supplied uv_buf_t structure. If NULL is assigned as the buffer’s base or 0 as its length, a UV_ENOBUFS error will be triggered in the uv_udp_recv_cb or the uv_read_cb callback.

A suggested size (65536 at the moment in most cases) is provided, but it’s just an indication, not related in any way to the pending data to be read. The user is free to allocate the amount of memory they decide.

As an example, applications with custom allocation schemes such as using freelists, allocation pools or slab based allocators may decide to use a different size which matches the memory chunks they already have.

Example:

static void my_alloc_cb(uv_handle_t* handle, size_t suggested_size, uv_buf_t* buf) {
  buf->base = malloc(suggested_size);
  buf->len = suggested_size;
}
void (*uv_close_cb)(uv_handle_t* handle)

Type definition for callback passed to uv_close().

Public members

uv_loop_t* uv_handle_t.loop

Pointer to the uv_loop_t where the handle is running on. Readonly.

uv_handle_type uv_handle_t.type

The uv_handle_type, indicating the type of the underlying handle. Readonly.

void* uv_handle_t.data

Space for user-defined arbitrary data. libuv does not use this field.

API

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.

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.

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.

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 Reference counting.

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 Reference counting.

int uv_has_ref(const uv_handle_t* handle)

Returns non-zero if the handle referenced, zero otherwise.

See Reference counting.

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 uv_handle_t argument but they work just for some handle types.

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.

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.

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.

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 uv_unref() after calling 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 uv_is_active() for a more detailed explanation on what being active involves.