From 3bfa915bde2415222d8dc048945f701353508160 Mon Sep 17 00:00:00 2001
From: Chris Howey <chris@howey.me>
Date: Thu, 6 Jun 2013 19:39:28 -0500
Subject: [PATCH] Linux - use select to see if any watch data

With this fix, we can check if Close() has been called on the
Watcher after every select. Before the Read would block indefinately,
possibly hanging forever (user calling watch.Close() when no events
available).
---
 fsnotify_linux.go | 47 ++++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 42 insertions(+), 5 deletions(-)

diff --git a/fsnotify_linux.go b/fsnotify_linux.go
index d74b8e5..53a5442 100644
--- a/fsnotify_linux.go
+++ b/fsnotify_linux.go
@@ -54,6 +54,9 @@ const (
 	sys_IN_IGNORED    uint32 = syscall.IN_IGNORED
 	sys_IN_Q_OVERFLOW uint32 = syscall.IN_Q_OVERFLOW
 	sys_IN_UNMOUNT    uint32 = syscall.IN_UNMOUNT
+
+	// Block for 100ms on each call to Select
+	selectWaitTime = 100e6
 )
 
 type FileEvent struct {
@@ -200,17 +203,37 @@ func (w *Watcher) readEvents() {
 		errno error                                   // Syscall errno
 	)
 
+	rfds := &syscall.FdSet{}
+	timeout := &syscall.Timeval{}
+
 	for {
-		n, errno = syscall.Read(w.fd, buf[0:])
+		// Select to see if data available
+		*timeout = syscall.NsecToTimeval(selectWaitTime)
+		FD_ZERO(rfds)
+		FD_SET(rfds, w.fd)
+		if _, errno = syscall.Select(w.fd+1, rfds, nil, nil, timeout); errno != nil {
+			w.Error <- os.NewSyscallError("select", errno)
+		}
+
 		// See if there is a message on the "done" channel
-		var done bool
 		select {
-		case done = <-w.done:
+		case <-w.done:
+			syscall.Close(w.fd)
+			close(w.internalEvent)
+			close(w.Error)
+			return
 		default:
 		}
 
-		// If EOF or a "done" message is received
-		if n == 0 || done {
+		// Check select result to see if Read will block, only read if no blocking.
+		if FD_ISSET(rfds, w.fd) {
+			n, errno = syscall.Read(w.fd, buf[0:])
+		} else {
+			continue
+		}
+
+		// If EOF is received
+		if n == 0 {
 			syscall.Close(w.fd)
 			close(w.internalEvent)
 			close(w.Error)
@@ -293,3 +316,17 @@ func (e *FileEvent) ignoreLinux() bool {
 	}
 	return false
 }
+
+func FD_SET(p *syscall.FdSet, i int) {
+	p.Bits[i/64] |= 1 << uint(i) % 64
+}
+
+func FD_ISSET(p *syscall.FdSet, i int) bool {
+	return (p.Bits[i/64] & (1 << uint(i) % 64)) != 0
+}
+
+func FD_ZERO(p *syscall.FdSet) {
+	for i := range p.Bits {
+		p.Bits[i] = 0
+	}
+}
-- 
2.50.1