Use resettable sync.Once instead of reassignment

Godeps/_workspace/src/github.com/matryer/resync/.gitignore

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+# Compiled Object files, Static and Dynamic libs (Shared Objects)
+*.o
+*.a
+*.so
+
+# Folders
+_obj
+_test
+
+# Architecture specific extensions/prefixes
+*.[568vq]
+[568vq].out
+
+*.cgo1.go
+*.cgo2.c
+_cgo_defun.c
+_cgo_gotypes.go
+_cgo_export.*
+
+_testmain.go
+
+*.exe
+*.test
+*.prof

Godeps/_workspace/src/github.com/matryer/resync/README.md

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+# resync
+
+`sync.Once` with `Reset()`
+
+  * See [sync.Once](http://golang.org/pkg/sync/#Once)
+
+## Example
+
+The following example examines how `resync.Once` could be used in a HTTP server situation.
+
+```
+// use it just like sync.Once
+var once resync.Once
+
+// handle a web request
+func handleRequest(w http.ResponseWriter, r *http.Request) {
+	once.Do(func(){
+		// load templates or something
+	})
+	// TODO: respond
+}
+
+// handle some request that indicates things have changed
+func handleResetRequest(w http.ResponseWriter, r *http.Request) {
+	once.Reset() // call Reset to cause initialisation to happen again above
+}
+```

Godeps/_workspace/src/github.com/matryer/resync/once.go

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+package resync
+
+import (
+	"sync"
+	"sync/atomic"
+)
+
+// Once is an object that will perform exactly one action
+// until Reset is called.
+// See http://golang.org/pkg/sync/#Once
+type Once struct {
+	m    sync.Mutex
+	done uint32
+}
+
+// Do simulates sync.Once.Do by executing the specified function
+// only once, until Reset is called.
+// See http://golang.org/pkg/sync/#Once
+func (o *Once) Do(f func()) {
+	if atomic.LoadUint32(&o.done) == 1 {
+		return
+	}
+	// Slow-path.
+	o.m.Lock()
+	defer o.m.Unlock()
+	if o.done == 0 {
+		defer atomic.StoreUint32(&o.done, 1)
+		f()
+	}
+}
+
+// Reset indicates that the next call to Do should actually be called
+// once again.
+func (o *Once) Reset() {
+	o.m.Lock()
+	defer o.m.Unlock()
+	atomic.StoreUint32(&o.done, 0)
+}

Godeps/_workspace/src/github.com/matryer/resync/once_test.go

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+package resync_test
+
+import (
+	"testing"
+
+	"github.com/cheekybits/is"
+	"github.com/khlieng/dispatch/Godeps/_workspace/src/github.com/matryer/resync"
+)
+
+func TestOnceReset(t *testing.T) {
+	is := is.New(t)
+	var calls int
+	var c resync.Once
+	c.Do(func() {
+		calls++
+	})
+	c.Do(func() {
+		calls++
+	})
+	c.Do(func() {
+		calls++
+	})
+	is.Equal(calls, 1)
+	c.Reset()
+	c.Do(func() {
+		calls++
+	})
+	c.Do(func() {
+		calls++
+	})
+	c.Do(func() {
+		calls++
+	})
+	is.Equal(calls, 2)
+}