Fix thread safety issue

VersionedMap.cpp

@@ -530,7 +530,7 @@ struct VersionedMap::Impl {
     int len;
   };
 
-  Finger search(Key key, int64_t at) const {
+  template <std::memory_order kOrder> Finger search(Key key, int64_t at) const {
     Finger finger;
     bool ignored;
     finger.push(latestRoot, ignored);
@@ -546,8 +546,7 @@ struct VersionedMap::Impl {
         // No duplicates
         break;
       }
-      finger.push(child<std::memory_order_relaxed>(n, c > 0, latestVersion),
-                  c > 0);
+      finger.push(child<kOrder>(n, c > 0, latestVersion), c > 0);
     }
     return finger;
   }
@@ -745,7 +744,8 @@ struct VersionedMap::Impl {
       case Clear: {
         insert({m.param1, m.param1Len}, {{nullptr, -1}});
         if (m.param2Len > 0) {
-          auto iter = search({m.param1, m.param1Len}, latestVersion);
+          auto iter = search<std::memory_order_relaxed>({m.param1, m.param1Len},
+                                                        latestVersion);
           move<std::memory_order_relaxed>(iter, latestVersion, true);
           while (iter.searchPathSize() > 0 &&
                  mm.base[iter.backNode()] < Key{m.param2, m.param2Len}) {
@@ -925,7 +925,7 @@ void VersionedMap::Impl::firstGeq(const Key *key, const int64_t *version,
   // TODO ILP!
   for (int i = 0; i < count; ++i) {
     // TODO re-use root if passed-in iterator version matches
-    auto finger = search(key[i], version[i]);
+    auto finger = search<std::memory_order_acquire>(key[i], version[i]);
     if (iterator[i].impl != nullptr) {
       iterator[i].impl->~Impl();
     }