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// Copyright (c) 2017 CtrlC developers
// Licensed under the Apache License, Version 2.0
// <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT
// license <LICENSE-MIT or http://opensource.org/licenses/MIT>,
// at your option. All files in the project carrying such
// notice may not be copied, modified, or distributed except
// according to those terms.

#![warn(missing_docs)]

//! Cross platform handling of Ctrl-C signals.
//!
//! [HandlerRoutine]:https://msdn.microsoft.com/en-us/library/windows/desktop/ms683242.aspx
//!
//! [set_handler()](fn.set_handler.html) allows setting a handler closure which is executed on
//! `Ctrl+C`. On Unix, this corresponds to a `SIGINT` signal. On windows, `Ctrl+C` corresponds to
//! [`CTRL_C_EVENT`][HandlerRoutine] or [`CTRL_BREAK_EVENT`][HandlerRoutine].
//!
//! Setting a handler will start a new dedicated signal handling thread where we
//! execute the handler each time we receive a `Ctrl+C` signal. There can only be
//! one handler, you would typically set one at the start of your program.
//!
//! # Example
//! ```no_run
//! extern crate ctrlc;
//! use std::sync::atomic::{AtomicBool, Ordering};
//! use std::sync::Arc;
//!
//! fn main() {
//!     let running = Arc::new(AtomicBool::new(true));
//!     let r = running.clone();
//!
//!     ctrlc::set_handler(move || {
//!         r.store(false, Ordering::SeqCst);
//!     }).expect("Error setting Ctrl-C handler");
//!
//!     println!("Waiting for Ctrl-C...");
//!     while running.load(Ordering::SeqCst) {}
//!     println!("Got it! Exiting...");
//! }
//! ```
//!
//! # Handling SIGTERM
//! Handling of `SIGTERM` can be enabled with `termination` feature. If this is enabled,
//! the handler specified by `set_handler()` will be executed for both `SIGINT` and `SIGTERM`.
//!

mod error;
mod platform;

pub use error::Error;
use std::sync::atomic::{AtomicBool, Ordering, ATOMIC_BOOL_INIT};
use std::thread;

static INIT: AtomicBool = ATOMIC_BOOL_INIT;

/// Register signal handler for Ctrl-C.
///
/// Starts a new dedicated signal handling thread. Should only be called once,
/// typically at the start of your program.
///
/// # Example
/// ```no_run
/// ctrlc::set_handler(|| println!("Hello world!")).expect("Error setting Ctrl-C handler");
/// ```
///
/// # Warning
/// On Unix, any existing `SIGINT`, `SIGTERM`(if termination feature is enabled) or `SA_SIGINFO`
/// posix signal handlers will be overwritten. On Windows, multiple handler routines are allowed,
/// but they are called on a last-registered, first-called basis until the signal is handled.
///
/// On Unix, signal dispositions and signal handlers are inherited by child processes created via
/// `fork(2)` on, but not by child processes created via `execve(2)`.
/// Signal handlers are not inherited on Windows.
///
/// # Errors
/// Will return an error if another `ctrlc::set_handler()` handler exists or if a
/// system error occurred while setting the handler.
///
/// # Panics
/// Any panic in the handler will not be caught and will cause the signal handler thread to stop.
///
pub fn set_handler<F>(user_handler: F) -> Result<(), Error>
where
    F: Fn() -> () + 'static + Send,
{
    if INIT.compare_and_swap(false, true, Ordering::SeqCst) {
        return Err(Error::MultipleHandlers);
    }

    unsafe {
        match platform::init_os_handler() {
            Ok(_) => {}
            err => {
                INIT.store(false, Ordering::SeqCst);
                return err;
            }
        }
    }

    thread::spawn(move || loop {
        unsafe {
            platform::block_ctrl_c().expect("Critical system error while waiting for Ctrl-C");
        }
        user_handler();
    });

    Ok(())
}