Introduce try_set_handler

Revert set_handler to overwrite signal handlers, introduce
try_set_handler that does not overwrite existing handlers.

src/lib.rs

@@ -73,30 +73,51 @@ static INIT_LOCK: Mutex<()> = Mutex::new(());
 /// ```
 ///
 /// # Warning
-/// On Unix, the handler registration for `SIGINT`, (`SIGTERM` and `SIGHUP` if termination feature is enabled) or `SA_SIGINFO`
-/// posix signal handlers will fail if a signal handler is already present. 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, the handler registration for `SIGINT`, (`SIGTERM` and `SIGHUP` 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.
+///
+/// ctrlc::try_set_handler will error (on Unix) if another signal handler exists for the same
+/// signal(s) that ctrlc is trying to attach the handler to.
 ///
 /// 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.
+/// Will return an error 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: FnMut() + 'static + Send,
+{
+    init_and_set_handler(user_handler, true)
+}
+
+/// The same as ctrlc::set_handler but errors if a handler already exists for the signal(s).
+///
+/// # Errors
+/// Will return an error if another handler exists or if a system error occurred while setting the
+/// handler.
+pub fn try_set_handler<F>(user_handler: F) -> Result<(), Error>
+where
+    F: FnMut() + 'static + Send,
+{
+    init_and_set_handler(user_handler, false)
+}
+
+fn init_and_set_handler<F>(user_handler: F, overwrite: bool) -> Result<(), Error>
 where
     F: FnMut() + 'static + Send,
 {
     if !INIT.load(Ordering::Acquire) {
         let _guard = INIT_LOCK.lock().unwrap();
 
         if !INIT.load(Ordering::Relaxed) {
-            set_handler_inner(user_handler)?;
+            set_handler_inner(user_handler, overwrite)?;
             INIT.store(true, Ordering::Release);
             return Ok(());
         }
@@ -105,12 +126,12 @@ where
     Err(Error::MultipleHandlers)
 }
 
-fn set_handler_inner<F>(mut user_handler: F) -> Result<(), Error>
+fn set_handler_inner<F>(mut user_handler: F, overwrite: bool) -> Result<(), Error>
 where
     F: FnMut() + 'static + Send,
 {
     unsafe {
-        match platform::init_os_handler() {
+        match platform::init_os_handler(overwrite) {
             Ok(_) => {}
             Err(err) => {
                 return Err(err.into());

src/platform/unix/mod.rs

@@ -83,7 +83,7 @@ fn pipe2(flags: nix::fcntl::OFlag) -> nix::Result<(RawFd, RawFd)> {
 /// Will return an error if a system error occurred.
 ///
 #[inline]
-pub unsafe fn init_os_handler() -> Result<(), Error> {
+pub unsafe fn init_os_handler(overwrite: bool) -> Result<(), Error> {
     use nix::fcntl;
     use nix::sys::signal;
 
@@ -113,7 +113,7 @@ pub unsafe fn init_os_handler() -> Result<(), Error> {
         Ok(old) => old,
         Err(e) => return Err(close_pipe(e)),
     };
-    if sigint_old.handler() != signal::SigHandler::SigDfl {
+    if !overwrite && sigint_old.handler() != signal::SigHandler::SigDfl {
         signal::sigaction(signal::Signal::SIGINT, &sigint_old).unwrap();
         return Err(close_pipe(nix::Error::EEXIST));
     }
@@ -127,7 +127,7 @@ pub unsafe fn init_os_handler() -> Result<(), Error> {
                 return Err(close_pipe(e));
             }
         };
-        if sigterm_old.handler() != signal::SigHandler::SigDfl {
+        if !overwrite && sigterm_old.handler() != signal::SigHandler::SigDfl {
             signal::sigaction(signal::Signal::SIGINT, &sigint_old).unwrap();
             signal::sigaction(signal::Signal::SIGTERM, &sigterm_old).unwrap();
             return Err(close_pipe(nix::Error::EEXIST));
@@ -140,7 +140,7 @@ pub unsafe fn init_os_handler() -> Result<(), Error> {
                 return Err(close_pipe(e));
             }
         };
-        if sighup_old.handler() != signal::SigHandler::SigDfl {
+        if !overwrite && sighup_old.handler() != signal::SigHandler::SigDfl {
             signal::sigaction(signal::Signal::SIGINT, &sigint_old).unwrap();
             signal::sigaction(signal::Signal::SIGTERM, &sigterm_old).unwrap();
             signal::sigaction(signal::Signal::SIGHUP, &sighup_old).unwrap();

src/platform/windows/mod.rs

@@ -41,7 +41,7 @@ unsafe extern "system" fn os_handler(_: u32) -> BOOL {
 /// Will return an error if a system error occurred.
 ///
 #[inline]
-pub unsafe fn init_os_handler() -> Result<(), Error> {
+pub unsafe fn init_os_handler(_overwrite: bool) -> Result<(), Error> {
     SEMAPHORE = CreateSemaphoreA(ptr::null_mut(), 0, MAX_SEM_COUNT, ptr::null());
     if SEMAPHORE == 0 {
         return Err(io::Error::last_os_error());

tests/main/issue_97.rs

@@ -16,7 +16,7 @@ use test_signal_hook::run_signal_hook;
 
 fn expect_multiple_handlers() {
     #[cfg(not(windows))]
-    match ctrlc::set_handler(|| {}) {
+    match ctrlc::try_set_handler(|| {}) {
         Err(ctrlc::Error::MultipleHandlers) => {}
         _ => panic!("Expected Error::MultipleHandlers"),
     }

tests/main/mod.rs

@@ -11,9 +11,6 @@
 mod harness;
 use harness::{platform, run_harness};
 
-mod test_signal_hook;
-use test_signal_hook::run_signal_hook;
-
 use std::sync::{
     atomic::{AtomicBool, Ordering},
     Arc,
@@ -42,7 +39,6 @@ fn test_set_handler() {
 
 fn tests() {
     run_tests!(test_set_handler);
-    run_tests!(run_signal_hook);
 }
 
 fn main() {