#ifndef __TclObjCache_h_
#define __TclObjCache_h_

#include <tcl.h>
#include <map>
#include <string>

#include "../shared/TclUtil.h"
#include "../shared/ThreadMonitor.h"


/* Don't convert from strings to objects any more than we have to.  This is
 * especially useful for scripts which are compiled.  But it could apply to
 * data objects, too.  
 *
 * It's hard to do this in any smart way.  Objects cannot be shared between
 * threads.  Threads are pooled, so work may be sent from one thread to the
 * next at any time.  When we save a data value, we have no idea if it will
 * be read back by this thread or another.  When we know we are done with a
 * script, we have no convenient way to notify all threads that we are done
 * with it.
 *
 * Thought for the future, not urgent:
 * Many data objects will be stored in the database.  The database does not
 * give us Tcl objects.  If we were smart, we could probably recreate these
 * efficiently without caching.  Ideally we'd use the mysql commands which
 * return integers and doubles in their native form, rather than as strings.
 *
 * http://dev.mysql.com/doc/refman/5.5/en/mysql-stmt-fetch.html#id1363684
 */

class TclObjCache : private ThreadMonitor::Extra, NoCopy, NoAssign
{
private:
  const size_t _maxCacheSize;
  // _hot contains all cached items that we have used recently.  _cold contains
  // items that might or might not have been used recently.  Some keys may be
  // in both maps; in that case they will both point to the same value so it
  // doesn't matter which we use.  When it's time to clear old values from the
  // cache, _cold gets emptied, then we move everything from _hot to _cold,
  // leaving _hot empty.
  std::map< std::string, TclObjHolder > _hot, _cold;
  TclObjCache();
  bool cacheDisabled() const { return _maxCacheSize == 0; }
  void clearOldValues();
  static TclObjHolder create(std::string const &asString);

  // from ThreadMonitor::Extra
  virtual std::string getInfoForThreadMonitor();
  
public:
  ~TclObjCache();
  TclObjHolder find(std::string const &asString);
  static TclObjCache &getInstance();
};


#endif