Added NameMapperProxy from kiwix/kiwix-desktop#714

The right place for NameMapperProxy introduced by
kiwix/kiwix-desktop#714 is in libkiwix (so that it can be reused in
kiwix-serve).

include/name_mapper.h

@@ -22,6 +22,8 @@
 
 #include <string>
 #include <map>
+#include <memory>
+#include <mutex>
 
 namespace kiwix
 {
@@ -54,7 +56,24 @@ class HumanReadableNameMapper : public NameMapper {
     virtual std::string getIdForName(const std::string& name);
 };
 
+class NameMapperProxy : public kiwix::NameMapper {
+    typedef std::shared_ptr<kiwix::NameMapper> NameMapperHandle;
+  public:
+    explicit NameMapperProxy(kiwix::Library& library);
+
+    virtual std::string getNameForId(const std::string& id);
+    virtual std::string getIdForName(const std::string& name);
+
+    void update();
 
+  private:
+    NameMapperHandle currentNameMapper() const;
+
+  private:
+    mutable std::mutex mutex;
+    kiwix::Library& library;
+    NameMapperHandle nameMapper;
+};
 
 }
 

src/name_mapper.cpp

@@ -59,4 +59,45 @@ std::string HumanReadableNameMapper::getIdForName(const std::string& name) {
   return m_nameToId.at(name);
 }
 
+////////////////////////////////////////////////////////////////////////////////
+// NameMapperProxy
+////////////////////////////////////////////////////////////////////////////////
+
+NameMapperProxy::NameMapperProxy(Library& lib)
+  : library(lib)
+{
+  update();
+}
+
+void NameMapperProxy::update()
+{
+  const auto newNameMapper = new HumanReadableNameMapper(library, false);
+  std::lock_guard<std::mutex> lock(mutex);
+  nameMapper.reset(newNameMapper);
+}
+
+NameMapperProxy::NameMapperHandle
+NameMapperProxy::currentNameMapper() const
+{
+  // Return a copy of the handle to the current NameMapper object. It will
+  // ensure that the object survives any call to NameMapperProxy::update()
+  // made before the completion of any pending operation on that object.
+  std::lock_guard<std::mutex> lock(mutex);
+  return nameMapper;
+}
+
+std::string NameMapperProxy::getNameForId(const std::string& id)
+{
+  // Ensure that the current nameMapper object survives a concurrent call
+  // to NameMapperProxy::update()
+  return currentNameMapper()->getNameForId(id);
+}
+
+std::string NameMapperProxy::getIdForName(const std::string& name)
+{
+  // Ensure that the current nameMapper object survives a concurrent call
+  // to NameMapperProxy::update()
+  return currentNameMapper()->getIdForName(name);
+}
+
 }