Handle timeout and refactor the blocking logic in epoll_wait

Author: tiif

src/shims/unix/linux/epoll.rs

@@ -430,7 +430,7 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
         let epfd_value = this.read_scalar(epfd)?.to_i32()?;
         let events = this.read_immediate(events_op)?;
         let maxevents = this.read_scalar(maxevents)?.to_i32()?;
-        let timeout = this.read_scalar(timeout)?.to_u32()?;
+        let timeout = this.read_scalar(timeout)?.to_i32()?;
 
         if epfd_value <= 0 || maxevents <= 0 {
             let einval = this.eval_libc("EINVAL");
@@ -467,42 +467,43 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
             ready_list_empty = binding.borrow_mut().is_empty();
             thread_ids = epoll_file_description.thread_id.borrow_mut();
         }
-
-        if ready_list_empty {
-            if timeout == 0 {
-                // Non-blocking with no notification returned.
-                this.write_scalar(Scalar::from_i32(0), &dest)?;
-            } else {
-                // Blocking
-                let duration = Duration::from_millis(timeout.into());
-                thread_ids.push(this.active_thread());
-                this.block_thread(
-                    BlockReason::Epoll,
-                    Some((TimeoutClock::Monotonic, TimeoutAnchor::Relative, duration)),
-                    callback!(
-                        @capture<'tcx> {
-                            epfd_value: i32,
-                            weak_epfd: WeakFileDescriptionRef,
-                            dest: MPlaceTy<'tcx>,
-                            event: MPlaceTy<'tcx>,
-                        }
-                        @unblock = |this| {
-                            this.blocking_epoll_callback(epfd_value, weak_epfd, &dest, &event)?;
-                            Ok(())
-                        }
-                        @timeout = |this| {
-                            // No notification after blocking timeout.
-                            this.write_scalar(Scalar::from_i32(0), &dest)?;
-                            Ok(())
-                        }
-                    ),
-                );
-            }
-        } else {
-            // Immediately return epoll notification without blocking.
+        if timeout == 0 || !ready_list_empty {
+            // If the ready list is not empty, or the timeout is 0, we can return immediately.
             this.blocking_epoll_callback(epfd_value, weak_epfd, &dest, &event)?;
+        } else {
+            // Blocking
+            let timeout = match timeout {
+                0.. => {
+                    let duration = Duration::from_millis(timeout.try_into().unwrap());
+                    Some((TimeoutClock::Monotonic, TimeoutAnchor::Relative, duration))
+                }
+                // If timeout value less than 0, block indefinitely until a notification
+                // is returned.
+                ..0 => None,
+            };
+            thread_ids.push(this.active_thread());
+            this.block_thread(
+                BlockReason::Epoll,
+                timeout,
+                callback!(
+                    @capture<'tcx> {
+                        epfd_value: i32,
+                        weak_epfd: WeakFileDescriptionRef,
+                        dest: MPlaceTy<'tcx>,
+                        event: MPlaceTy<'tcx>,
+                    }
+                    @unblock = |this| {
+                        this.blocking_epoll_callback(epfd_value, weak_epfd, &dest, &event)?;
+                        Ok(())
+                    }
+                    @timeout = |this| {
+                        // No notification after blocking timeout.
+                        this.write_scalar(Scalar::from_i32(0), &dest)?;
+                        Ok(())
+                    }
+                ),
+            );
         }
-
         Ok(())
     }