Fix signal handling on Unix systems

This removes the the signal handling machinery in tty::unix, and
replaces it with functionality from signal-hook, which should be more
robust. Signals caught by signal-hook wake up the existing I/O event
loop, which then delegates back to the PTY to handle them.

In particular, this allows `SIGCHLD` (i.e. child process exits) to shut
down the terminal promptly, instead of sometimes leaving the window
lingering.

Fixes #915.
Fixes #1276.
Fixes #1313.

As a side effect, this fixes a very rare bug on Linux, where a `read`
from the PTY on the master side would sometimes "fail" with `EIO` if the
child closed the client side at a particular moment. This was subject to
a race condition, and was very difficult to trigger in practice.

1 files changed, 3 insertions, 1 deletions

diff --git a/src/term/mod.rs b/src/term/mod.rs
index 63b0ca80..fc59ffd6 100644
--- a/src/term/mod.rs
+++ b/src/term/mod.rs
@@ -34,6 +34,8 @@ use crate::url::UrlParser;
 use crate::message_bar::MessageBuffer;
 use crate::term::color::Rgb;
 use crate::term::cell::{LineLength, Cell};
+
+#[cfg(windows)]
 use crate::tty;
 
 pub mod cell;
@@ -1336,7 +1338,7 @@ impl Term {
 
     #[inline]
     pub fn should_exit(&self) -> bool {
-        tty::process_should_exit() || self.should_exit
+        self.should_exit
     }
 }