# `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 `uv_tty_t` handle libuv will only detect size changes when the cursor is moved. When a readable `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.

Changed in version 1.15.0: SIGWINCH support on Windows was improved.

Changed in version 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

type uv_signal_t

  Signal handle type.

typedef void (*uv_signal_cb)(uv_signal_t *handle, int signum)

  Type definition for callback passed to `uv_signal_start()`.

### Public members

int uv_signal_t.signum

  Signal being monitored by this handle. Readonly.

See also

The `uv_handle_t` members also apply.

## API

int uv_signal_init(uv_loop_t *loop, uv_signal_t *signal)

  Initialize the handle.

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.

int uv_signal_start_oneshot(uv_signal_t *signal, uv_signal_cb cb, int signum)

  New in version 1.12.0.

  Same functionality as `uv_signal_start()` but the signal handler is reset the moment the signal is received.

int uv_signal_stop(uv_signal_t *signal)

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

See also

The `uv_handle_t` API functions also apply.