From 8941e9a90b9560e6b433c68725255f827922a5a8 Mon Sep 17 00:00:00 2001
From: Luke Shumaker <lukeshu@sbcglobal.net>
Date: Sat, 12 Sep 2015 09:14:40 -0600
Subject: Add an inotify watcher utility using channels; use it.

The interface of inotify/inutil.Watcher more resembles
golang.org/x/exp/inotify; with it using channels instead of repeated calls
to Read().

In my use-case, this is useful because it allows implementing a "read"
(select, really) that doesn't block Close(); which is required to handle
the TERM signal correctly.
---
 inotify/inutil/inotify_util.go | 78 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 78 insertions(+)
 create mode 100644 inotify/inutil/inotify_util.go

diff --git a/inotify/inutil/inotify_util.go b/inotify/inutil/inotify_util.go
new file mode 100644
index 0000000..46146f5
--- /dev/null
+++ b/inotify/inutil/inotify_util.go
@@ -0,0 +1,78 @@
+package inutil
+
+import (
+        "inotify"
+        "os"
+        "syscall"
+)
+
+const (
+	// Flags for the parameter of InotifyInit1().
+	// These, oddly, appear to be 24-bit numbers.
+	IN_CLOEXEC  = inotify.IN_CLOEXEC
+)
+
+type Watcher struct {
+        Events <-chan inotify.Event
+        events chan<- inotify.Event
+        Errors <-chan error
+        errors chan<- error
+        in *inotify.Inotify
+}
+
+func WatcherInit() (*Watcher, error) {
+        in, err := inotify.InotifyInit()
+        return newWatcher(in, err)
+}
+
+func WatcherInit1(flags int) (*Watcher, error) {
+        in, err := inotify.InotifyInit1(flags&^inotify.IN_NONBLOCK)
+        return newWatcher(in, err)
+}
+
+func newWatcher(in *inotify.Inotify, err error) (*Watcher, error) {
+        events := make(chan inotify.Event, 1)
+        errors := make(chan error, 1)
+        o := &Watcher{
+                Events: events,
+                events: events,
+                Errors: errors,
+                errors: errors,
+                in: in,
+        }
+        go o.worker()
+        return o, err
+}
+
+func (o *Watcher) AddWatch(path string, mask inotify.Mask) (inotify.Wd, error) {
+        return o.in.AddWatch(path, mask);
+}
+
+func (o *Watcher) RmWatch(wd inotify.Wd) error {
+        return o.in.RmWatch(wd);
+}
+
+func (o *Watcher) Close() {
+        func() {
+                defer recover()
+                close(o.events)
+                close(o.errors)
+        }()
+        go o.in.Close()
+}
+
+func (o *Watcher) worker() {
+        defer recover()
+        for {
+		ev, err := o.in.Read();
+		if ev.Wd >= 0 {
+                        o.events <- ev
+                }
+                if err != nil {
+                        if err.(*os.SyscallError).Err == syscall.EBADF {
+                                o.Close()
+                        }
+                        o.errors <- err
+		}
+	}
+}
-- 
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