Auto merge of #76919 - fusion-engineering-forks:thread-parker, r=dtolnay

Use futex-based thread::park/unpark on Linux.

This moves the parking/unparking logic out of `thread/mod.rs` into a module named `thread_parker` in `sys_common`. The current implementation is moved to `sys_common/thread_parker/generic.rs` and the new implementation using futexes is added in `sys_common/thread_parker/futex.rs`.

library/std/src/sys/unix/futex.rs

@@ -0,0 +1,37 @@
+#![cfg(any(target_os = "linux", target_os = "android"))]
+
+use crate::convert::TryInto;
+use crate::ptr::null;
+use crate::sync::atomic::AtomicI32;
+use crate::time::Duration;
+
+pub fn futex_wait(futex: &AtomicI32, expected: i32, timeout: Option<Duration>) {
+    let timespec = timeout.and_then(|d| {
+        Some(libc::timespec {
+            // Sleep forever if the timeout is longer than fits in a timespec.
+            tv_sec: d.as_secs().try_into().ok()?,
+            // This conversion never truncates, as subsec_nanos is always <1e9.
+            tv_nsec: d.subsec_nanos() as _,
+        })
+    });
+    unsafe {
+        libc::syscall(
+            libc::SYS_futex,
+            futex as *const AtomicI32,
+            libc::FUTEX_WAIT | libc::FUTEX_PRIVATE_FLAG,
+            expected,
+            timespec.as_ref().map_or(null(), |d| d as *const libc::timespec),
+        );
+    }
+}
+
+pub fn futex_wake(futex: &AtomicI32) {
+    unsafe {
+        libc::syscall(
+            libc::SYS_futex,
+            futex as *const AtomicI32,
+            libc::FUTEX_WAKE | libc::FUTEX_PRIVATE_FLAG,
+            1,
+        );
+    }
+}

library/std/src/sys/unix/mod.rs

@@ -49,6 +49,7 @@ pub mod env;
 pub mod ext;
 pub mod fd;
 pub mod fs;
+pub mod futex;
 pub mod io;
 #[cfg(target_os = "l4re")]
 mod l4re;