add original source

source/listing_3.13.cpp

@@ -0,0 +1,30 @@
+#include <map>
+#include <string>
+#include <mutex>
+#include <boost/thread/shared_mutex.hpp>
+
+class dns_entry
+{};
+
+class dns_cache
+{
+    std::map<std::string,dns_entry> entries;
+    boost::shared_mutex entry_mutex;
+public:
+    dns_entry find_entry(std::string const& domain)
+    {
+        boost::shared_lock<boost::shared_mutex> lk(entry_mutex);
+        std::map<std::string,dns_entry>::const_iterator const it=
+            entries.find(domain);
+        return (it==entries.end())?dns_entry():it->second;
+    }
+    void update_or_add_entry(std::string const& domain,
+                             dns_entry const& dns_details)
+    {
+        std::lock_guard<boost::shared_mutex> lk(entry_mutex);
+        entries[domain]=dns_details;
+    }
+};
+
+int main()
+{}