Unifi reaper logic into package

Signed-off-by: Michael Crosby <crosbymichael@gmail.com>

sys/reaper/reaper_unix.go

@@ -0,0 +1,109 @@
+// +build !windows
+
+/*
+   Copyright The containerd Authors.
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+*/
+
+package reaper
+
+import (
+	"os/exec"
+	"sync"
+	"time"
+
+	"github.com/containerd/containerd/sys"
+	runc "github.com/containerd/go-runc"
+	"github.com/pkg/errors"
+)
+
+// ErrNoSuchProcess is returned when the process no longer exists
+var ErrNoSuchProcess = errors.New("no such process")
+
+const bufferSize = 2048
+
+// Reap should be called when the process receives an SIGCHLD.  Reap will reap
+// all exited processes and close their wait channels
+func Reap() error {
+	now := time.Now()
+	exits, err := sys.Reap(false)
+	Default.Lock()
+	for c := range Default.subscribers {
+		for _, e := range exits {
+			c <- runc.Exit{
+				Timestamp: now,
+				Pid:       e.Pid,
+				Status:    e.Status,
+			}
+		}
+	}
+	Default.Unlock()
+	return err
+}
+
+// Default is the default monitor initialized for the package
+var Default = &Monitor{
+	subscribers: make(map[chan runc.Exit]struct{}),
+}
+
+// Monitor monitors the underlying system for process status changes
+type Monitor struct {
+	sync.Mutex
+
+	subscribers map[chan runc.Exit]struct{}
+}
+
+// Start starts the command a registers the process with the reaper
+func (m *Monitor) Start(c *exec.Cmd) (chan runc.Exit, error) {
+	ec := m.Subscribe()
+	if err := c.Start(); err != nil {
+		m.Unsubscribe(ec)
+		return nil, err
+	}
+	return ec, nil
+}
+
+// Wait blocks until a process is signal as dead.
+// User should rely on the value of the exit status to determine if the
+// command was successful or not.
+func (m *Monitor) Wait(c *exec.Cmd, ec chan runc.Exit) (int, error) {
+	for e := range ec {
+		if e.Pid == c.Process.Pid {
+			// make sure we flush all IO
+			c.Wait()
+			m.Unsubscribe(ec)
+			return e.Status, nil
+		}
+	}
+	// return no such process if the ec channel is closed and no more exit
+	// events will be sent
+	return -1, ErrNoSuchProcess
+}
+
+// Subscribe to process exit changes
+func (m *Monitor) Subscribe() chan runc.Exit {
+	c := make(chan runc.Exit, bufferSize)
+	m.Lock()
+	m.subscribers[c] = struct{}{}
+	m.Unlock()
+	return c
+}
+
+// Unsubscribe to process exit changes
+func (m *Monitor) Unsubscribe(c chan runc.Exit) {
+	m.Lock()
+	delete(m.subscribers, c)
+	close(c)
+	m.Unlock()
+}