refactor: remove child ownership from Exit filter (#207)

Pid is used instead

src/os/kqueue.rs

@@ -7,6 +7,7 @@ use crate::Async;
 
 use std::future::Future;
 use std::io::{Error, Result};
+use std::num::NonZeroI32;
 use std::os::unix::io::{AsFd, AsRawFd, BorrowedFd, OwnedFd, RawFd};
 use std::pin::Pin;
 use std::process::Child;
@@ -238,18 +239,30 @@ impl Queueable for Signal {}
 /// When registered into [`Async`](crate::Async) via [`with_filter`](AsyncKqueueExt::with_filter),
 /// it will return a [`readable`](crate::Async::readable) event when the child process exits.
 #[derive(Debug)]
-pub struct Exit(Option<Child>);
+pub struct Exit(NonZeroI32);
 
 impl Exit {
     /// Create a new `Exit` object.
     pub fn new(child: Child) -> Self {
-        Self(Some(child))
+        Self(
+            NonZeroI32::new(child.id().try_into().expect("unable to parse pid"))
+                .expect("cannot register pid with zero value"),
+        )
+    }
+
+    /// Create a new `Exit` object from a PID.
+    ///
+    /// # Safety
+    ///
+    /// The PID must be tied to an actual child process.
+    pub unsafe fn from_pid(pid: NonZeroI32) -> Self {
+        Self(pid)
     }
 }
 
 impl QueueableSealed for Exit {
     fn registration(&mut self) -> Registration {
-        Registration::Process(self.0.take().expect("Cannot reregister child"))
+        Registration::Process(self.0)
     }
 }
 impl Queueable for Exit {}

src/reactor/kqueue.rs

@@ -7,8 +7,8 @@ use polling::{Event, PollMode, Poller};
 
 use std::fmt;
 use std::io::Result;
+use std::num::NonZeroI32;
 use std::os::unix::io::{AsRawFd, BorrowedFd, RawFd};
-use std::process::Child;
 
 /// The raw registration into the reactor.
 ///
@@ -27,8 +27,8 @@ pub enum Registration {
     /// Raw signal number for signal delivery.
     Signal(Signal),
 
-    /// Process for process termination.
-    Process(Child),
+    /// Pid for process termination.
+    Process(NonZeroI32),
 }
 
 impl fmt::Debug for Registration {
@@ -62,8 +62,8 @@ impl Registration {
             Self::Signal(signal) => {
                 poller.add_filter(PollSignal(signal.0), token, PollMode::Oneshot)
             }
-            Self::Process(process) => poller.add_filter(
-                unsafe { Process::new(process, ProcessOps::Exit) },
+            Self::Process(pid) => poller.add_filter(
+                unsafe { Process::from_pid(*pid, ProcessOps::Exit) },
                 token,
                 PollMode::Oneshot,
             ),
@@ -82,8 +82,8 @@ impl Registration {
             Self::Signal(signal) => {
                 poller.modify_filter(PollSignal(signal.0), interest.key, PollMode::Oneshot)
             }
-            Self::Process(process) => poller.modify_filter(
-                unsafe { Process::new(process, ProcessOps::Exit) },
+            Self::Process(pid) => poller.modify_filter(
+                unsafe { Process::from_pid(*pid, ProcessOps::Exit) },
                 interest.key,
                 PollMode::Oneshot,
             ),
@@ -100,8 +100,8 @@ impl Registration {
                 poller.delete(fd)
             }
             Self::Signal(signal) => poller.delete_filter(PollSignal(signal.0)),
-            Self::Process(process) => {
-                poller.delete_filter(unsafe { Process::new(process, ProcessOps::Exit) })
+            Self::Process(pid) => {
+                poller.delete_filter(unsafe { Process::from_pid(*pid, ProcessOps::Exit) })
             }
         }
     }