Add a way to get the global poller's fd

Author: notgull

src/lib.rs

@@ -88,6 +88,8 @@ use crate::reactor::{Reactor, Source};
 mod driver;
 mod reactor;
 
+pub mod os;
+
 pub use driver::block_on;
 pub use reactor::{Readable, ReadableOwned, Writable, WritableOwned};
 

src/os.rs

@@ -0,0 +1,4 @@
+//! Platform-specific functionality.
+
+#[cfg(unix)]
+pub mod unix;

src/os/unix.rs

@@ -0,0 +1,33 @@
+//! Functionality that is only available for `unix` platforms.
+
+#[cfg(not(async_io_no_io_safety))]
+use std::os::unix::io::BorrowedFd;
+
+/// Get a file descriptor that can be used to wait for readiness in an external runtime.
+#[cfg(not(async_io_no_io_safety))]
+pub fn reactor_fd() -> Option<BorrowedFd<'static>> {
+    cfg_if::cfg_if! {
+        if #[cfg(all(
+            any(
+                target_os = "linux",
+                target_os = "android",
+                target_os = "illumos",
+                target_os = "solaris",
+                target_os = "macos",
+                target_os = "ios",
+                target_os = "tvos",
+                target_os = "watchos",
+                target_os = "freebsd",
+                target_os = "netbsd",
+                target_os = "openbsd",
+                target_os = "dragonfly",
+            ),
+            not(polling_test_poll_backend),
+        ))] {
+            use std::os::unix::io::AsFd;
+            Some(crate::Reactor::get().poller.as_fd())
+        } else {
+            None
+        }
+    }
+}

src/reactor.rs

@@ -32,7 +32,7 @@ pub(crate) struct Reactor {
     /// Portable bindings to epoll/kqueue/event ports/IOCP.
     ///
     /// This is where I/O is polled, producing I/O events.
-    poller: Poller,
+    pub(crate) poller: Poller,
 
     /// Ticker bumped before polling.
     ///