      1
      2
      3
      4
      5
      6
      7
      8
      9
     10
     11
     12
     13
     14
     15
     16
     17
     18
     19
     20
     21
     22
     23
     24
     25
     26
     27
     28
     29
     30
     31
     32
     33
     34
     35
     36
     37
     38
     39
     40
     41
     42
     43
     44
     45
     46
     47
     48
     49
     50
     51
     52
     53
     54
     55
     56
     57
     58
     59
     60
     61
     62
     63
     64
     65
     66
     67
     68
     69
     70
     71
     72
     73
     74
     75
     76
     77
     78
     79
     80
     81
     82
     83
     84
     85
     86
     87
     88
     89
     90
     91
     92
     93
     94
     95
     96
     97
     98
     99
    100
    101
    102
    103
    104
    105
    106
    107
    108
    109
    110
    111
    112
    113
    114
    115
    116
    117
    118
    119
    120
    121
    122
    123
    124
    125
    126
    127
    128
    129
    130
    131
    132
    133
    134
    135
    136
    137
    138
    139
    140
    141
    142
    143
    144
    145
    146
    147
    148
    149
    150
    151
    152
    153
    154
    155
    156
    157
    158
    159
    160
    161
    162
    163
    164
    165
    166
    167
    168
    169
    170
    171
    172
    173
    174
    175
    176
    177
    178
    179
    180
    181
    182
    183
    184
    185
    186
    187
    188
    189
    190
    191
    192
    193
    194
    195
    196
    197
    198
    199
    200
    201
    202
    203
    204
    205
    206
    207
    208
    209
    210
    211
    212
    213
    214
    215
    216
    217

    use std::io;
    use std::process::ExitStatus;
    use std::sync::Mutex;

    /// 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 reaping a set of orphaned processes.
    pub(crate) trait ReapOrphanQueue {
        /// Attempts 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: ReapOrphanQueue> ReapOrphanQueue for &T {
        fn reap_orphans(&self) {
            (**self).reap_orphans()
        }
    }

    /// An interface for queueing up an orphaned process so that it can be reaped.
    pub(crate) trait OrphanQueue<T>: ReapOrphanQueue {
        /// Adds an orphan to the queue.
        fn push_orphan(&self, orphan: T);
    }

    impl<T, O: OrphanQueue<T>> OrphanQueue<T> for &O {
        fn push_orphan(&self, orphan: T) {
            (**self).push_orphan(orphan);
        }
    }

    /// An implementation of `OrphanQueue`.
    #[derive(Debug)]
    pub(crate) struct OrphanQueueImpl<T> {
        queue: Mutex<Vec<T>>,
    }

    impl<T> OrphanQueueImpl<T> {
        pub(crate) fn new() -> Self {
            Self {
                queue: Mutex::new(Vec::new()),
            }
        }

        #[cfg(test)]
        fn len(&self) -> usize {
            self.queue.lock().unwrap().len()
        }
    }

    impl<T: Wait> OrphanQueue<T> for OrphanQueueImpl<T> {
        fn push_orphan(&self, orphan: T) {
            self.queue.lock().unwrap().push(orphan)
        }
    }

    impl<T: Wait> ReapOrphanQueue for OrphanQueueImpl<T> {
        fn reap_orphans(&self) {
            let mut queue = self.queue.lock().unwrap();
            let queue = &mut *queue;

            for i in (0..queue.len()).rev() {
                match queue[i].try_wait() {
                    Ok(None) => {}
                    Ok(Some(_)) | Err(_) => {
                        // The stdlib handles interruption errors (EINTR) when polling a child process.
                        // All other errors represent invalid inputs or pids that have already been
                        // reaped, so we can drop the orphan in case an error is raised.
                        queue.swap_remove(i);
                    }
                }
            }
        }
    }

    #[cfg(all(test, not(loom)))]
    pub(crate) mod test {
        use super::*;
        use std::cell::{Cell, RefCell};
        use std::io;
        use std::os::unix::process::ExitStatusExt;
        use std::process::ExitStatus;
        use std::rc::Rc;

        pub(crate) struct MockQueue<W> {
            pub(crate) all_enqueued: RefCell<Vec<W>>,
            pub(crate) total_reaps: Cell<usize>,
        }

        impl<W> MockQueue<W> {
            pub(crate) fn new() -> Self {
                Self {
                    all_enqueued: RefCell::new(Vec::new()),
                    total_reaps: Cell::new(0),
                }
            }
        }

        impl<W> OrphanQueue<W> for MockQueue<W> {
            fn push_orphan(&self, orphan: W) {
                self.all_enqueued.borrow_mut().push(orphan);
            }
        }

        impl<W> ReapOrphanQueue for MockQueue<W> {
            fn reap_orphans(&self) {
                self.total_reaps.set(self.total_reaps.get() + 1);
            }
        }

        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 = OrphanQueueImpl::new();
            orphanage.push_orphan(first_orphan);
            orphanage.push_orphan(third_orphan);
            orphanage.push_orphan(second_orphan);
            orphanage.push_orphan(fourth_orphan);

            assert_eq!(orphanage.len(), 4);

            orphanage.reap_orphans();
            assert_eq!(orphanage.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.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.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
        }
    }