code review 4817058: runtime: fix data race in findfunc()

src/pkg/runtime/arm/atomic.c

 // Copyright 2009 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.
 
 #include "runtime.h"
 
 // Atomic add and return new value.
 #pragma textflag 7
 uint32
 runtime·xadd(uint32 volatile *val, int32 delta)
 {
         uint32 oval, nval;
 
         for(;;){
                 oval = *val;
                 nval = oval + delta;
                 if(runtime·cas(val, oval, nval))
                         return nval;
+        }
+}
+
+#pragma textflag 7
+uint32
+runtime·xchg(uint32 volatile* addr, uint32 v)
+{
+        uint32 old;
+
+        for(;;) {
+                old = *addr;
+                if(runtime·cas(addr, old, v))
+                        return old;
+        }
+}
+
+#pragma textflag 7
+void
+runtime·procyield(uint32 cnt)
+{
+        uint32 volatile i;
+
+        for(i = 0; i < cnt; i++) {
         }
 }
 
 #pragma textflag 7
 uint32
 runtime·atomicload(uint32 volatile* addr)
 {
         return runtime·xadd(addr, 0);
 }
 
@@ skipping 22 matching lines @@
 runtime·atomicstore(uint32 volatile* addr, uint32 v)
 {
         uint32 old;
 ········
         for(;;) {
                 old = *addr;
                 if(runtime·cas(addr, old, v))
                         return;
         }
 }