Auto merge of #57714 - matthewjasper:wellformed-unreachable, r=pnkfelix

[rust.git] / src / libcore / hint.rs

diff --git a/src/libcore/hint.rs b/src/libcore/hint.rs
index 9e57a4ebc991983f58d0a8a9a7fe62bfbe7fcfff..ad5a2071a7381c033bd5243441753b775f154a39 100644 (file)
--- a/src/libcore/hint.rs
+++ b/src/libcore/hint.rs
@@ -49,3 +49,26 @@
 pub unsafe fn unreachable_unchecked() -> ! {
     intrinsics::unreachable()
 }
+
+/// Save power or switch hyperthreads in a busy-wait spin-loop.
+///
+/// This function is deliberately more primitive than
+/// [`std::thread::yield_now`](../../std/thread/fn.yield_now.html) and
+/// does not directly yield to the system's scheduler.
+/// In some cases it might be useful to use a combination of both functions.
+/// Careful benchmarking is advised.
+///
+/// On some platforms this function may not do anything at all.
+#[inline]
+#[unstable(feature = "renamed_spin_loop", issue = "55002")]
+pub fn spin_loop() {
+    #[cfg(any(target_arch = "x86", target_arch = "x86_64"))]
+    unsafe {
+        asm!("pause" ::: "memory" : "volatile");
+    }
+
+    #[cfg(target_arch = "aarch64")]
+    unsafe {
+        asm!("yield" ::: "memory" : "volatile");
+    }
+}