.. _signal:

:c:type:`uv_signal_t` --- Signal handle
=======================================

Signal handles implement Unix style signal handling on a per-event loop bases.

Windows notes
-------------

Reception of some signals is emulated:

* SIGINT is normally delivered when the user presses CTRL+C. However, like
  on Unix, it is not generated when terminal raw mode is enabled.

* SIGBREAK is delivered when the user pressed CTRL + BREAK.

* SIGHUP is generated when the user closes the console window. On SIGHUP the
  program is given approximately 10 seconds to perform cleanup. After that
  Windows will unconditionally terminate it.

* SIGWINCH is raised whenever libuv detects that the console has been
  resized. When a libuv app is running under a console emulator, or when a
  32-bit libuv app is running on 64-bit system, SIGWINCH will be emulated. In
  such cases SIGWINCH signals may not always be delivered in a timely manner.
  For a writable :c:type:`uv_tty_t` handle libuv will only detect size changes
  when the cursor is moved. When a readable :c:type:`uv_tty_t` handle is used,
  resizing of the console buffer will be detected only if the handle is in raw
  mode and is being read.

* Watchers for other signals can be successfully created, but these signals
  are never received. These signals are: `SIGILL`, `SIGABRT`, `SIGFPE`, `SIGSEGV`,
  `SIGTERM` and `SIGKILL.`

* Calls to raise() or abort() to programmatically raise a signal are
  not detected by libuv; these will not trigger a signal watcher.

.. versionchanged:: 1.15.0 SIGWINCH support on Windows was improved.
.. versionchanged:: 1.31.0 32-bit libuv SIGWINCH support on 64-bit Windows was
                           rolled back to old implementation.

Unix notes
----------

* SIGKILL and SIGSTOP are impossible to catch.

* Handling SIGBUS, SIGFPE, SIGILL or SIGSEGV via libuv results into undefined behavior.

* SIGABRT will not be caught by libuv if generated by `abort()`, e.g. through `assert()`.

* On Linux SIGRT0 and SIGRT1 (signals 32 and 33) are used by the NPTL pthreads library to
  manage threads. Installing watchers for those signals will lead to unpredictable behavior
  and is strongly discouraged. Future versions of libuv may simply reject them.


Data types
----------

.. c:type:: uv_signal_t

    Signal handle type.

.. c:type:: void (*uv_signal_cb)(uv_signal_t* handle, int signum)

    Type definition for callback passed to :c:func:`uv_signal_start`.


Public members
^^^^^^^^^^^^^^

.. c:member:: int uv_signal_t.signum

    Signal being monitored by this handle. Readonly.

.. seealso:: The :c:type:`uv_handle_t` members also apply.


API
---

.. c:function:: int uv_signal_init(uv_loop_t* loop, uv_signal_t* signal)

    Initialize the handle.

.. c:function:: int uv_signal_start(uv_signal_t* signal, uv_signal_cb cb, int signum)

    Start the handle with the given callback, watching for the given signal.

.. c:function:: int uv_signal_start_oneshot(uv_signal_t* signal, uv_signal_cb cb, int signum)

    .. versionadded:: 1.12.0

    Same functionality as :c:func:`uv_signal_start` but the signal handler is reset the moment
    the signal is received.

.. c:function:: int uv_signal_stop(uv_signal_t* signal)

    Stop the handle, the callback will no longer be called.

.. seealso:: The :c:type:`uv_handle_t` API functions also apply.