1 files changed, 61 insertions, 5 deletions

diff --git a/llgo/third_party/gofrontend/libgo/go/net/singleflight.go b/llgo/third_party/gofrontend/libgo/go/net/singleflight.go
index dc58affdaac..bf599f0cc94 100644
--- a/llgo/third_party/gofrontend/libgo/go/net/singleflight.go
+++ b/llgo/third_party/gofrontend/libgo/go/net/singleflight.go
@@ -8,10 +8,18 @@ import "sync"
 
 // call is an in-flight or completed singleflight.Do call
 type call struct {
-	wg   sync.WaitGroup
-	val  interface{}
-	err  error
-	dups int
+	wg sync.WaitGroup
+
+	// These fields are written once before the WaitGroup is done
+	// and are only read after the WaitGroup is done.
+	val interface{}
+	err error
+
+	// These fields are read and written with the singleflight
+	// mutex held before the WaitGroup is done, and are read but
+	// not written after the WaitGroup is done.
+	dups  int
+	chans []chan<- singleflightResult
 }
 
 // singleflight represents a class of work and forms a namespace in
@@ -21,6 +29,14 @@ type singleflight struct {
 	m  map[string]*call // lazily initialized
 }
 
+// singleflightResult holds the results of Do, so they can be passed
+// on a channel.
+type singleflightResult struct {
+	v      interface{}
+	err    error
+	shared bool
+}
+
 // Do executes and returns the results of the given function, making
 // sure that only one execution is in-flight for a given key at a
 // time. If a duplicate comes in, the duplicate caller waits for the
@@ -42,12 +58,52 @@ func (g *singleflight) Do(key string, fn func() (interface{}, error)) (v interfa
 	g.m[key] = c
 	g.mu.Unlock()
 
+	g.doCall(c, key, fn)
+	return c.val, c.err, c.dups > 0
+}
+
+// DoChan is like Do but returns a channel that will receive the
+// results when they are ready.
+func (g *singleflight) DoChan(key string, fn func() (interface{}, error)) <-chan singleflightResult {
+	ch := make(chan singleflightResult, 1)
+	g.mu.Lock()
+	if g.m == nil {
+		g.m = make(map[string]*call)
+	}
+	if c, ok := g.m[key]; ok {
+		c.dups++
+		c.chans = append(c.chans, ch)
+		g.mu.Unlock()
+		return ch
+	}
+	c := &call{chans: []chan<- singleflightResult{ch}}
+	c.wg.Add(1)
+	g.m[key] = c
+	g.mu.Unlock()
+
+	go g.doCall(c, key, fn)
+
+	return ch
+}
+
+// doCall handles the single call for a key.
+func (g *singleflight) doCall(c *call, key string, fn func() (interface{}, error)) {
 	c.val, c.err = fn()
 	c.wg.Done()
 
 	g.mu.Lock()
 	delete(g.m, key)
+	for _, ch := range c.chans {
+		ch <- singleflightResult{c.val, c.err, c.dups > 0}
+	}
 	g.mu.Unlock()
+}
 
-	return c.val, c.err, c.dups > 0
+// Forget tells the singleflight to forget about a key.  Future calls
+// to Do for this key will call the function rather than waiting for
+// an earlier call to complete.
+func (g *singleflight) Forget(key string) {
+	g.mu.Lock()
+	delete(g.m, key)
+	g.mu.Unlock()
 }