Allow sleep form of poll_oneoff for wasmtime-wasi (#8429)

* Allow sleep form of poll_oneoff for wasmtime-wasi

Allow sleep form of poll_oneoff for wasmtime-wasi crate, which just
sleeps for relative time using sleep from the std::thread.
This patch derives from the commit "Support sleep forms of poll_oneoff"
6b40724d18. Applying this patch would
help improve the real-time performance of wasmtime.

Closes #8428

Signed-off-by: Daichi Fukui <daichi1.fukui@toshiba.co.jp>

* Run cargo fmt

---------

Signed-off-by: Daichi Fukui <daichi1.fukui@toshiba.co.jp>
Co-authored-by: Alex Crichton <alex@alexcrichton.com>

crates/wasi/src/preview1.rs

@@ -2321,6 +2321,35 @@ impl wasi_snapshot_preview1::WasiSnapshotPreview1 for WasiP1Ctx {
             // Indefinite sleeping is not supported in preview1.
             return Err(types::Errno::Inval.into());
         }
+
+        // This is a special case where `poll_oneoff` is just sleeping
+        // on a single relative timer event. This special case was added
+        // after experimental observations showed that std::thread::sleep
+        // results in more consistent sleep times. This design ensures that
+        // wasmtime can handle real-time requirements more accurately.
+        if nsubscriptions == 1 {
+            let sub = subs.read()?;
+            if let types::SubscriptionU::Clock(clocksub) = sub.u {
+                if !clocksub
+                    .flags
+                    .contains(types::Subclockflags::SUBSCRIPTION_CLOCK_ABSTIME)
+                    && self.ctx().allow_blocking_current_thread
+                {
+                    std::thread::sleep(std::time::Duration::from_nanos(clocksub.timeout));
+                    events.write(types::Event {
+                        userdata: sub.userdata,
+                        error: types::Errno::Success,
+                        type_: types::Eventtype::Clock,
+                        fd_readwrite: types::EventFdReadwrite {
+                            flags: types::Eventrwflags::empty(),
+                            nbytes: 1,
+                        },
+                    })?;
+                    return Ok(1);
+                }
+            }
+        }
+
         let subs = subs.as_array(nsubscriptions);
         let events = events.as_array(nsubscriptions);