Use a `recursive_mutex` instead of a `mutex`.

This allow us to internally call thread_safe function from already
locked context.

include/library.h

@@ -408,7 +408,7 @@ private: // functions
   void dropCache(const std::string& bookId);
 
 private: //data
-  mutable std::mutex m_mutex;
+  mutable std::recursive_mutex m_mutex;
   Library::Revision m_revision;
   std::map<std::string, Entry> m_books;
   using ArchiveCache = ConcurrentCache<std::string, std::shared_ptr<zim::Archive>>;

src/library.cpp

@@ -110,7 +110,7 @@ Library::~Library() = default;
 
 bool Library::addBook(const Book& book)
 {
-  std::lock_guard<std::mutex> lock(m_mutex);
+  std::lock_guard<std::recursive_mutex> lock(m_mutex);
   ++m_revision;
   /* Try to find it */
   updateBookDB(book);
@@ -141,13 +141,13 @@ bool Library::addBook(const Book& book)
 
 void Library::addBookmark(const Bookmark& bookmark)
 {
-  std::lock_guard<std::mutex> lock(m_mutex);
+  std::lock_guard<std::recursive_mutex> lock(m_mutex);
   m_bookmarks.push_back(bookmark);
 }
 
 bool Library::removeBookmark(const std::string& zimId, const std::string& url)
 {
-  std::lock_guard<std::mutex> lock(m_mutex);
+  std::lock_guard<std::recursive_mutex> lock(m_mutex);
   for(auto it=m_bookmarks.begin(); it!=m_bookmarks.end(); it++) {
     if (it->getBookId() == zimId && it->getUrl() == url) {
       m_bookmarks.erase(it);
@@ -166,7 +166,7 @@ void Library::dropCache(const std::string& id)
 
 bool Library::removeBookById(const std::string& id)
 {
-  std::lock_guard<std::mutex> lock(m_mutex);
+  std::lock_guard<std::recursive_mutex> lock(m_mutex);
   m_bookDB->delete_document("Q" + id);
   dropCache(id);
   // We do not change the cache size here
@@ -184,7 +184,7 @@ bool Library::removeBookById(const std::string& id)
 
 Library::Revision Library::getRevision() const
 {
-  std::lock_guard<std::mutex> lock(m_mutex);
+  std::lock_guard<std::recursive_mutex> lock(m_mutex);
   return m_revision;
 }
 
@@ -192,7 +192,7 @@ uint32_t Library::removeBooksNotUpdatedSince(Revision libraryRevision)
 {
   BookIdCollection booksToRemove;
   {
-    std::lock_guard<std::mutex> lock(m_mutex);
+    std::lock_guard<std::recursive_mutex> lock(m_mutex);
     for ( const auto& entry : m_books) {
       if ( entry.second.lastUpdatedRevision <= libraryRevision ) {
         booksToRemove.push_back(entry.first);
@@ -217,7 +217,7 @@ const Book& Library::getBookById(const std::string& id) const
 
 Book Library::getBookByIdThreadSafe(const std::string& id) const
 {
-  std::lock_guard<std::mutex> lock(m_mutex);
+  std::lock_guard<std::recursive_mutex> lock(m_mutex);
   return getBookById(id);
 }
 
@@ -275,7 +275,7 @@ std::shared_ptr<ZimSearcher> Library::getSearcherByIds(const BookIdSet& ids)
 unsigned int Library::getBookCount(const bool localBooks,
                                    const bool remoteBooks) const
 {
-  std::lock_guard<std::mutex> lock(m_mutex);
+  std::lock_guard<std::recursive_mutex> lock(m_mutex);
   return getBookCount_not_protected(localBooks, remoteBooks);
 }
 
@@ -288,7 +288,7 @@ bool Library::writeToFile(const std::string& path) const
   dumper.setBaseDir(baseDir);
   std::string xml;
   {
-    std::lock_guard<std::mutex> lock(m_mutex);
+    std::lock_guard<std::recursive_mutex> lock(m_mutex);
     xml = dumper.dumpLibXMLContent(allBookIds);
   };
   return writeTextFile(path, xml);
@@ -304,7 +304,7 @@ bool Library::writeBookmarksToFile(const std::string& path) const
 
 Library::AttributeCounts Library::getBookAttributeCounts(BookStrPropMemFn p) const
 {
-  std::lock_guard<std::mutex> lock(m_mutex);
+  std::lock_guard<std::recursive_mutex> lock(m_mutex);
   AttributeCounts propValueCounts;
 
   for (const auto& pair: m_books) {
@@ -336,7 +336,7 @@ std::vector<std::string> Library::getBooksLanguages() const
 
 Library::AttributeCounts Library::getBooksLanguagesWithCounts() const
 {
-  std::lock_guard<std::mutex> lock(m_mutex);
+  std::lock_guard<std::recursive_mutex> lock(m_mutex);
   AttributeCounts langsWithCounts;
 
   for (const auto& pair: m_books) {
@@ -352,7 +352,7 @@ Library::AttributeCounts Library::getBooksLanguagesWithCounts() const
 
 std::vector<std::string> Library::getBooksCategories() const
 {
-  std::lock_guard<std::mutex> lock(m_mutex);
+  std::lock_guard<std::recursive_mutex> lock(m_mutex);
   std::set<std::string> categories;
 
   for (const auto& pair: m_books) {
@@ -383,7 +383,7 @@ const std::vector<kiwix::Bookmark> Library::getBookmarks(bool onlyValidBookmarks
   }
   std::vector<kiwix::Bookmark> validBookmarks;
   auto booksId = getBooksIds();
-  std::lock_guard<std::mutex> lock(m_mutex);
+  std::lock_guard<std::recursive_mutex> lock(m_mutex);
   for(auto& bookmark:m_bookmarks) {
     if (std::find(booksId.begin(), booksId.end(), bookmark.getBookId()) != booksId.end()) {
       validBookmarks.push_back(bookmark);
@@ -394,7 +394,7 @@ const std::vector<kiwix::Bookmark> Library::getBookmarks(bool onlyValidBookmarks
 
 Library::BookIdCollection Library::getBooksIds() const
 {
-  std::lock_guard<std::mutex> lock(m_mutex);
+  std::lock_guard<std::recursive_mutex> lock(m_mutex);
   BookIdCollection bookIds;
 
   for (auto& pair: m_books) {
@@ -600,7 +600,7 @@ Library::BookIdCollection Library::filterViaBookDB(const Filter& filter) const
 
   BookIdCollection bookIds;
 
-  std::lock_guard<std::mutex> lock(m_mutex);
+  std::lock_guard<std::recursive_mutex> lock(m_mutex);
   Xapian::Enquire enquire(*m_bookDB);
   enquire.set_query(query);
   const auto results = enquire.get_mset(0, m_books.size());
@@ -615,7 +615,7 @@ Library::BookIdCollection Library::filter(const Filter& filter) const
 {
   BookIdCollection result;
   const auto preliminaryResult = filterViaBookDB(filter);
-  std::lock_guard<std::mutex> lock(m_mutex);
+  std::lock_guard<std::recursive_mutex> lock(m_mutex);
   for(auto id : preliminaryResult) {
     if(filter.accept(m_books.at(id))) {
       result.push_back(id);
@@ -689,7 +689,7 @@ void Library::sort(BookIdCollection& bookIds, supportedListSortBy sort, bool asc
   // NOTE: for the entire duration of the sort. Will need to obtain (under a
   // NOTE: lock) the required atributes from the books once, and then the
   // NOTE: sorting will run on a copy of data without locking.
-  std::lock_guard<std::mutex> lock(m_mutex);
+  std::lock_guard<std::recursive_mutex> lock(m_mutex);
   switch(sort) {
     case TITLE:
       std::sort(bookIds.begin(), bookIds.end(), Comparator<TITLE>(this, ascending));