Use a set of id as key for a the searcher Cache.

It will allow use to cache seacher for multiple zim files.

src/library.cpp

@@ -59,6 +59,27 @@ bool booksReferToTheSameArchive(const Book& book1, const Book& book2)
       && book1.getPath() == book2.getPath();
 }
 
+template<typename Key, typename Value>
+class MultiKeyCache: public ConcurrentCache<std::set<Key>, Value>
+{
+  public:
+    explicit MultiKeyCache(size_t maxEntries)
+      : ConcurrentCache<std::set<Key>, Value>(maxEntries)
+    {}
+
+    bool drop(const Key& key)
+    {
+      std::unique_lock<std::mutex> l(this->lock_);
+      bool removed = false;
+      for(auto& cache_key: this->impl_.keys()) {
+        if(cache_key.find(key)!=cache_key.end()) {
+          removed |= this->impl_.drop(cache_key);
+        }
+      }
+      return removed;
+    }
+};
+
 } // unnamed namespace
 
 struct Library::Impl
@@ -72,7 +93,7 @@ struct Library::Impl
   std::map<std::string, Entry> m_books;
   using ArchiveCache = ConcurrentCache<std::string, std::shared_ptr<zim::Archive>>;
   std::unique_ptr<ArchiveCache> mp_archiveCache;
-  using SearcherCache = ConcurrentCache<std::string, std::shared_ptr<zim::Searcher>>;
+  using SearcherCache = MultiKeyCache<std::string, std::shared_ptr<zim::Searcher>>;
   std::unique_ptr<SearcherCache> mp_searcherCache;
   std::vector<kiwix::Bookmark> m_bookmarks;
   Xapian::WritableDatabase m_bookDB;
@@ -285,8 +306,9 @@ std::shared_ptr<zim::Archive> Library::getArchiveById(const std::string& id)
 
 std::shared_ptr<zim::Searcher> Library::getSearcherById(const std::string& id)
 {
+  std::set<std::string> ids {id};
   try {
-    return mp_impl->mp_searcherCache->getOrPut(id,
+    return mp_impl->mp_searcherCache->getOrPut(ids,
     [&](){
       auto archive = getArchiveById(id);
       if(!archive) {

src/tools/concurrent_cache.h

@@ -90,7 +90,7 @@ public: // types
     return  impl_.setMaxSize(new_size);
   }
 
-private: // data
+protected: // data
   Impl impl_;
   std::mutex lock_;
 };

src/tools/lrucache.h

@@ -144,6 +144,14 @@ public: // functions
     return previous;
   }
 
+  std::set<key_t> keys() const  {
+    std::set<key_t> keys;
+    for(auto& item:_cache_items_map) {
+      keys.insert(item.first);
+    }
+    return keys;
+  }
+
 private: // functions
   void putMissing(const key_t& key, const value_t& value) {
     assert(_cache_items_map.find(key) == _cache_items_map.end());