code review 3460042: netchan: fix dumb locking bug introduced in recent editing.

src/pkg/netchan/export.go

 // Copyright 2010 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
 /*
         The netchan package implements type-safe networked channels:
         it allows the two ends of a channel to appear on different
         computers connected by a network.  It does this by transporting
         data sent to a channel on one machine so it can be recovered
         by a receive of a channel of the same type on the other.
@@ skipping 253 matching lines @@
                         clients: make(map[unackedCounter]bool),
                 },
         }
         go e.listen()
         return e, nil
 }
 
 // addClient creates a new expClient and records its existence
 func (exp *Exporter) addClient(conn net.Conn) *expClient {
         client := newClient(exp, conn)
+        exp.mu.Lock()
         exp.clients[client] = true
         exp.mu.Unlock()
         return client
 }
 
 // delClient forgets the client existed
 func (exp *Exporter) delClient(client *expClient) {
         exp.mu.Lock()
         exp.clients[client] = false, false
         exp.mu.Unlock()
@@ skipping 74 matching lines @@
         if ok {
                 exp.chans[name] = nil, false
         }
         exp.mu.Unlock()
         if !ok {
                 return os.ErrorString("netchan export: hangup: no such channel: " + name)
         }
         chDir.ch.Close()
         return nil
 }