Added flush of a desired element in the cached_map.

The unit test is extended accordingly.

Author: marek-trtik

src/util/cached_map.h

@@ -509,6 +509,35 @@ class cached_mapt final
     base_map.flush();
   }
 
+  /*******************************************************************\
+
+  Function: cached_mapt::unload(const key_type &)
+
+  Inputs:
+    key: A key whose corresponding value should be unload.
+
+  Outputs:
+   True, if the referenced element was unload, and false otherwise.
+
+  Purpose:
+    Unloads the element referenced by the passed key in the cache to allow the
+    backing store to be externally manipulated.
+
+  Remarks:
+    This function will not unload a locked element.
+
+  \*******************************************************************/
+  bool unload(const key_type &key)
+  {
+    if(std::find(unloadable.cbegin(), unloadable.cend(), key)
+       == unloadable.cend())
+    {
+      return false;
+    }
+    base_map.set(key, remove_cache(key));
+    return true;
+  }
+
 private:
   std::shared_ptr<mapped_type> get(
     const key_type &key, std::function<mapped_type()> load_value) const

unit/serialization/cached_map.cpp

@@ -122,6 +122,17 @@ void test_cached_map()
   test_assert(map.cache_size() == 4, "The unloaded element can be reloaded");
   test_assert(map.size() == 4, "Map size is correct after element is reloaded");
 
-  // Now f4, f3 and f1 will be unlocked as they go out of scope
-  // Now f4, f3 and f1 will be unloaded as map goes out of scope
+  test_assert(map.locked_count() == 4,
+              "All 4 elements must be locked before flush");
+  test_assert(!map.unload(get_F_key(f2)),
+              "Flush must fail as the element 7 is locked");
+  // Now we unlock elements 1 and 7 respectively.
+  f41 = nullptr;
+  f22 = nullptr;
+  test_assert(map.locked_count() == 2,
+              "After unlocking 1 and 7 there must remain only 2 locked");
+  test_assert(map.unload(get_F_key(f2)),
+              "Flush of 7 must succeed as it was unlocked");
+
+  // Now 5, 9 and will be unloaded as map goes out of scope
 }