From 797a4574d1a733d4e3186a40d3e77dc0ab8c1278 Mon Sep 17 00:00:00 2001
From: Dan Gohman <dev@sunfishcode.online>
Date: Wed, 29 Nov 2023 09:14:13 -0800
Subject: [PATCH] Implement `pause`. (#948)

---
 src/backend/libc/event/syscalls.rs      |  8 +++++++
 src/backend/linux_raw/event/syscalls.rs | 21 ++++++++++++++++-
 src/event/mod.rs                        |  4 ++++
 src/event/pause.rs                      | 31 +++++++++++++++++++++++++
 4 files changed, 63 insertions(+), 1 deletion(-)
 create mode 100644 src/event/pause.rs

diff --git a/src/backend/libc/event/syscalls.rs b/src/backend/libc/event/syscalls.rs
index f2dcdf5ad..725ec8250 100644
--- a/src/backend/libc/event/syscalls.rs
+++ b/src/backend/libc/event/syscalls.rs
@@ -181,3 +181,11 @@ pub(crate) fn port_send(
 ) -> io::Result<()> {
     unsafe { ret(c::port_send(borrowed_fd(port), events, userdata)) }
 }
+
+#[cfg(not(any(windows, target_os = "redox", target_os = "wasi")))]
+pub(crate) fn pause() {
+    let r = unsafe { libc::pause() };
+    let errno = libc_errno::errno().0;
+    debug_assert_eq!(r, -1);
+    debug_assert_eq!(errno, libc::EINTR);
+}
diff --git a/src/backend/linux_raw/event/syscalls.rs b/src/backend/linux_raw/event/syscalls.rs
index 6cb8d3d96..0ae775339 100644
--- a/src/backend/linux_raw/event/syscalls.rs
+++ b/src/backend/linux_raw/event/syscalls.rs
@@ -9,7 +9,7 @@ use crate::backend::c;
 #[cfg(feature = "alloc")]
 use crate::backend::conv::pass_usize;
 use crate::backend::conv::{
-    by_ref, c_int, c_uint, raw_fd, ret, ret_owned_fd, ret_usize, slice_mut, zero,
+    by_ref, c_int, c_uint, raw_fd, ret, ret_error, ret_owned_fd, ret_usize, slice_mut, zero,
 };
 use crate::event::{epoll, EventfdFlags, PollFd};
 use crate::fd::{BorrowedFd, OwnedFd};
@@ -131,3 +131,22 @@ pub(crate) fn epoll_wait(
 pub(crate) fn eventfd(initval: u32, flags: EventfdFlags) -> io::Result<OwnedFd> {
     unsafe { ret_owned_fd(syscall_readonly!(__NR_eventfd2, c_uint(initval), flags)) }
 }
+
+#[inline]
+pub(crate) fn pause() {
+    unsafe {
+        #[cfg(any(target_arch = "aarch64", target_arch = "riscv64"))]
+        let error = ret_error(syscall_readonly!(
+            __NR_ppoll,
+            zero(),
+            zero(),
+            zero(),
+            zero()
+        ));
+
+        #[cfg(not(any(target_arch = "aarch64", target_arch = "riscv64")))]
+        let error = ret_error(syscall_readonly!(__NR_pause));
+
+        debug_assert_eq!(error, io::Errno::INTR);
+    }
+}
diff --git a/src/event/mod.rs b/src/event/mod.rs
index b0b62e0a6..b6b7f9971 100644
--- a/src/event/mod.rs
+++ b/src/event/mod.rs
@@ -9,6 +9,8 @@
 mod eventfd;
 #[cfg(all(feature = "alloc", bsd))]
 pub mod kqueue;
+#[cfg(not(any(windows, target_os = "redox", target_os = "wasi")))]
+mod pause;
 mod poll;
 #[cfg(solarish)]
 pub mod port;
@@ -22,4 +24,6 @@ pub use crate::backend::event::epoll;
     target_os = "espidf"
 ))]
 pub use eventfd::{eventfd, EventfdFlags};
+#[cfg(not(any(windows, target_os = "redox", target_os = "wasi")))]
+pub use pause::*;
 pub use poll::{poll, PollFd, PollFlags};
diff --git a/src/event/pause.rs b/src/event/pause.rs
new file mode 100644
index 000000000..f19108490
--- /dev/null
+++ b/src/event/pause.rs
@@ -0,0 +1,31 @@
+use crate::backend;
+
+/// `pause()`
+///
+/// The POSIX `pause` interface returns an error code, but the only thing
+/// `pause` does is sleep until interrupted by a signal, so it always
+/// returns the same thing with the same error code, so in rustix, the
+/// return value is omitted.
+///
+/// # References
+///  - [POSIX]
+///  - [Linux]
+///  - [Apple]
+///  - [FreeBSD]
+///  - [NetBSD]
+///  - [OpenBSD]
+///  - [DragonFly BSD]
+///  - [illumos]
+///
+/// [POSIX]: https://pubs.opengroup.org/onlinepubs/9699919799/functions/pause.html
+/// [Linux]: https://man7.org/linux/man-pages/man2/pause.2.html
+/// [Apple]: https://developer.apple.com/library/archive/documentation/System/Conceptual/ManPages_iPhoneOS/man3/pause.3.html
+/// [FreeBSD]: https://man.freebsd.org/cgi/man.cgi?query=pause&sektion=3
+/// [NetBSD]: https://man.netbsd.org/pause.3
+/// [OpenBSD]: https://man.openbsd.org/pause.3
+/// [DragonFly BSD]: https://man.dragonflybsd.org/?command=pause&section=3
+/// [illumos]: https://illumos.org/man/2/pause
+#[inline]
+pub fn pause() {
+    backend::event::syscalls::pause()
+}