1 files changed, 190 insertions, 0 deletions
diff --git a/tokio/src/process/unix/orphan.rs b/tokio/src/process/unix/orphan.rs
new file mode 100644
index 00000000..c02c903f
--- /dev/null
+++ b/tokio/src/process/unix/orphan.rs
@@ -0,0 +1,190 @@
+use crossbeam_queue::SegQueue;
+use std::io;
+use std::process::ExitStatus;
+
+/// An interface for waiting on a process to exit.
+pub(crate) trait Wait {
+    /// Get the identifier for this process or diagnostics.
+    fn id(&self) -> u32;
+    /// Try waiting for a process to exit in a non-blocking manner.
+    fn try_wait(&mut self) -> io::Result<Option<ExitStatus>>;
+}
+
+impl<T: Wait> Wait for &mut T {
+    fn id(&self) -> u32 {
+        (**self).id()
+    }
+
+    fn try_wait(&mut self) -> io::Result<Option<ExitStatus>> {
+        (**self).try_wait()
+    }
+}
+
+/// An interface for queueing up an orphaned process so that it can be reaped.
+pub(crate) trait OrphanQueue<T> {
+    /// Add an orphan to the queue.
+    fn push_orphan(&self, orphan: T);
+    /// Attempt to reap every process in the queue, ignoring any errors and
+    /// enqueueing any orphans which have not yet exited.
+    fn reap_orphans(&self);
+}
+
+impl<T, O: OrphanQueue<T>> OrphanQueue<T> for &O {
+    fn push_orphan(&self, orphan: T) {
+        (**self).push_orphan(orphan);
+    }
+
+    fn reap_orphans(&self) {
+        (**self).reap_orphans()
+    }
+}
+
+/// An atomic implementation of `OrphanQueue`.
+#[derive(Debug)]
+pub(crate) struct AtomicOrphanQueue<T> {
+    queue: SegQueue<T>,
+}
+
+impl<T> AtomicOrphanQueue<T> {
+    pub(crate) fn new() -> Self {
+        Self {
+            queue: SegQueue::new(),
+        }
+    }
+}
+
+impl<T: Wait> OrphanQueue<T> for AtomicOrphanQueue<T> {
+    fn push_orphan(&self, orphan: T) {
+        self.queue.push(orphan)
+    }
+
+    fn reap_orphans(&self) {
+        let len = self.queue.len();
+
+        if len == 0 {
+            return;
+        }
+
+        let mut orphans = Vec::with_capacity(len);
+        while let Ok(mut orphan) = self.queue.pop() {
+            match orphan.try_wait() {
+                Ok(Some(_)) => {}
+                Err(_) => {
+                    // TODO: bubble up error some how. Is this an internal bug?
+                    // Shoudl we panic? Is it OK for this to be silently
+                    // dropped?
+                }
+                // Still not done yet, we need to put it back in the queue
+                // when were done draining it, so that we don't get stuck
+                // in an infinite loop here
+                Ok(None) => orphans.push(orphan),
+            }
+        }
+
+        for orphan in orphans {
+            self.queue.push(orphan);
+        }
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::Wait;
+    use super::{AtomicOrphanQueue, OrphanQueue};
+    use std::cell::Cell;
+    use std::io;
+    use std::os::unix::process::ExitStatusExt;
+    use std::process::ExitStatus;
+    use std::rc::Rc;
+
+    struct MockWait {
+        total_waits: Rc<Cell<usize>>,
+        num_wait_until_status: usize,
+        return_err: bool,
+    }
+
+    impl MockWait {
+        fn new(num_wait_until_status: usize) -> Self {
+            Self {
+                total_waits: Rc::new(Cell::new(0)),
+                num_wait_until_status,
+                return_err: false,
+            }
+        }
+
+        fn with_err() -> Self {
+            Self {
+                total_waits: Rc::new(Cell::new(0)),
+                num_wait_until_status: 0,
+                return_err: true,
+            }
+        }
+    }
+
+    impl Wait for MockWait {
+        fn id(&self) -> u32 {
+            42
+        }
+
+        fn try_wait(&mut self) -> io::Result<Option<ExitStatus>> {
+            let waits = self.total_waits.get();
+
+            let ret = if self.num_wait_until_status == waits {
+                if self.return_err {
+                    Ok(Some(ExitStatus::from_raw(0)))
+                } else {
+                    Err(io::Error::new(io::ErrorKind::Other, "mock err"))
+                }
+            } else {
+                Ok(None)
+            };
+
+            self.total_waits.set(waits + 1);
+            ret
+        }
+    }
+
+    #[test]
+    fn drain_attempts_a_single_reap_of_all_queued_orphans() {
+        let first_orphan = MockWait::new(0);
+        let second_orphan = MockWait::new(1);
+        let third_orphan = MockWait::new(2);
+        let fourth_orphan = MockWait::with_err();
+
+        let first_waits = first_orphan.total_waits.clone();
+        let second_waits = second_orphan.total_waits.clone();
+        let third_waits = third_orphan.total_waits.clone();
+        let fourth_waits = fourth_orphan.total_waits.clone();
+
+        let orphanage = AtomicOrphanQueue::new();
+        orphanage.push_orphan(first_orphan);
+        orphanage.push_orphan(third_orphan);
+        orphanage.push_orphan(second_orphan);
+        orphanage.push_orphan(fourth_orphan);
+
+        assert_eq!(orphanage.queue.len(), 4);
+
+        orphanage.reap_orphans();
+        assert_eq!(orphanage.queue.len(), 2);
+        assert_eq!(first_waits.get(), 1);
+        assert_eq!(second_waits.get(), 1);
+        assert_eq!(third_waits.get(), 1);
+        assert_eq!(fourth_waits.get(), 1);
+
+        orphanage.reap_orphans();
+        assert_eq!(orphanage.queue.len(), 1);
+        assert_eq!(first_waits.get(), 1);
+        assert_eq!(second_waits.get(), 2);
+        assert_eq!(third_waits.get(), 2);
+        assert_eq!(fourth_waits.get(), 1);
+
+        orphanage.reap_orphans();
+        assert_eq!(orphanage.queue.len(), 0);
+        assert_eq!(first_waits.get(), 1);
+        assert_eq!(second_waits.get(), 2);
+        assert_eq!(third_waits.get(), 3);
+        assert_eq!(fourth_waits.get(), 1);
+
+        orphanage.reap_orphans(); // Safe to reap when empty
+    }
+}