Makes CultureInfo.get_Parent thread safe (#8656)

src/mscorlib/src/System/Globalization/CultureInfo.cs

@@ -893,29 +893,31 @@ public virtual CultureInfo Parent
  get
  {
  Contract.Ensures(Contract.Result<CultureInfo>() != null);
+ CultureInfo culture = null;
 
  if (null == m_parent)
  {
  try
  {
  string parentName = this.m_cultureData.SPARENT;
-
  if (String.IsNullOrEmpty(parentName))
  {
- m_parent = InvariantCulture;
+ culture = InvariantCulture;
  }
  else
  {
- m_parent = new CultureInfo(parentName, this.m_cultureData.UseUserOverride);
+ culture = new CultureInfo(parentName, this.m_cultureData.UseUserOverride);
  }
  }
  catch (ArgumentException)
  {
  // For whatever reason our IPARENT or SPARENT wasn't correct, so use invariant
  // We can't allow ourselves to fail. In case of custom cultures the parent of the
  // current custom culture isn't installed.
- m_parent = InvariantCulture;
+ culture = InvariantCulture;
  }
+
+ Interlocked.CompareExchange<CultureInfo>(ref m_parent, culture, null);
  }
  return m_parent;
  }