TFile.hxx

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/// \file ROOT/TFile.h
/// \ingroup Base ROOT7
/// \author Axel Naumann <axel@cern.ch>
/// \date 2015-07-31
/// \warning This is part of the ROOT 7 prototype! It will change without notice. It might trigger earthquakes. Feedback
/// is welcome!

/*************************************************************************
 * Copyright (C) 1995-2016, Rene Brun and Fons Rademakers.               *
 * All rights reserved.                                                  *
 *                                                                       *
 * For the licensing terms see $ROOTSYS/LICENSE.                         *
 * For the list of contributors see $ROOTSYS/README/CREDITS.             *
 *************************************************************************/

#ifndef ROOT7_TFile
#define ROOT7_TFile

#include "ROOT/TDirectory.hxx"

#include "TClass.h"

#include "RStringView.h"
#include <memory>
#include <typeinfo>

namespace ROOT {
namespace Experimental {

class TFilePtr;

namespace Internal {
class TFileStorageInterface;
class TFileSharedPtrCtor;
} // namespace Internal

/** \class ROOT::Experimental::TFile
 A ROOT file.

 A ROOT file is an object store: it can serialize any
 object for which ROOT I/O is available (generally: an object which has a
 dictionary), and it stores the object's data under a key name.

 */
class TFile: public TDirectory {
private:
   std::unique_ptr<Internal::TFileStorageInterface> fStorage; ///< Storage backend.

   TFile(std::unique_ptr<Internal::TFileStorageInterface> &&storage);

   /// Serialize the object at address, using the object's TClass.
   // FIXME: what about `cl` "pointing" to a base class?
   void WriteMemoryWithType(std::string_view name, const void *address, TClass *cl);

   friend Internal::TFileSharedPtrCtor;

public:
   /// Options for TFile construction.
   struct Options_t {
      /// Default constructor needed for member inits.
      Options_t() {}

      /// Whether the file should be opened asynchronously, if available.
      bool fAsynchronousOpen = false;

      /// Timeout for asynchronous opening.
      int fAsyncTimeout = 0;

      /// Whether the file should be cached before reading. Only available for
      /// "remote" file protocols. If the download fails, the file will be opened
      /// remotely.
      bool fCachedRead = false;

      /// Where to cache the file. If empty, defaults to TFilePtr::GetCacheDir().
      std::string fCacheDir;
   };

   ///\name Generator functions
   ///\{

   /// Open a file with `name` for reading.
   ///
   /// \note: Synchronizes multi-threaded accesses through locks.
   static TFilePtr Open(std::string_view name, const Options_t &opts = Options_t());

   /// Open an existing file with `name` for reading and writing. If a file with
   /// that name does not exist, an invalid TFilePtr will be returned.
   ///
   /// \note: Synchronizes multi-threaded accesses through locks.
   static TFilePtr OpenForUpdate(std::string_view name, const Options_t &opts = Options_t());

   /// Open a file with `name` for reading and writing. Fail (return an invalid
   /// `TFilePtr`) if a file with this name already exists.
   ///
   /// \note: Synchronizes multi-threaded accesses through locks.
   static TFilePtr Create(std::string_view name, const Options_t &opts = Options_t());

   /// Open a file with `name` for reading and writing. If a file with this name
   /// already exists, delete it and create a new one. Else simply create a new file.
   ///
   /// \note: Synchronizes multi-threaded accesses through locks.
   static TFilePtr Recreate(std::string_view name, const Options_t &opts = Options_t());

   ///\}

   /// Set the new directory used for cached reads, returns the old directory.
   ///
   /// \note: Synchronizes multi-threaded accesses through locks.
   static std::string SetCacheDir(std::string_view path);

   /// Get the directory used for cached reads.
   static std::string GetCacheDir();

   /// Must not call Write() of all attached objects:
   /// some might not be needed to be written or writing might be aborted due to
   /// an exception; require explicit Write().
   ~TFile();

   /// Save all objects associated with this directory (including file header) to
   /// the storage medium.
   void Flush();

   /// Flush() and make the file non-writable: close it.
   void Close();

   /// Read the object for a key. `T` must be the object's type.
   /// This will re-read the object for each call, returning a new copy; whether
   /// the `TDirectory` is managing an object attached to this key or not.
   /// \returns a `unique_ptr` to the object.
   /// \throws TDirectoryUnknownKey if no object is stored under this name.
   /// \throws TDirectoryTypeMismatch if the object stored under this name is of
   ///   a type different from `T`.
   template <class T>
   std::unique_ptr<T> Read(std::string_view name)
   {
      // FIXME: need separate collections for a TDirectory's key/value and registered objects. Here, we want to emit a
      // read and must look through the key/values without attaching an object to the TDirectory.
      // FIXME: do not register read object in TDirectory
      // FIXME: implement actual read
      // FIXME: for now, copy out of whatever the TDirectory manages.
      return std::make_unique<T>(*Get<T>(name));
   }

   /// Write an object that is not lifetime managed by this TFileImplBase.
   template <class T>
   void Write(std::string_view name, const T &obj)
   {
      WriteMemoryWithType(name, &obj, TClass::GetClass(typeid(T)));
   }

   /// Write an object that is not lifetime managed by this TFileImplBase.
   template <class T>
   void Write(std::string_view name, const T *obj)
   {
      WriteMemoryWithType(name, obj, TClass::GetClass(typeid(T)));
   }

   /// Write an object that is already lifetime managed by this TFileImplBase.
   void Write(std::string_view name)
   {
      auto dep = Find(name);
      WriteMemoryWithType(name, dep.GetPointer().get(), dep.GetType());
   }

   /// Hand over lifetime management of an object to this TFileImplBase, and
   /// write it.
   template <class T>
   void Write(std::string_view name, std::shared_ptr<T> &&obj)
   {
      Add(name, obj);
      // FIXME: use an iterator from the insertion to write instead of a second name lookup.
      Write(name);
   }
};

/**
 \class TFilePtr
 \brief Points to an object that stores or reads objects in ROOT's binary
 format.

 FIXME: implement async open; likely using std::future, possibly removing the
 Option_t element.

 */

class TFilePtr {
private:
   std::shared_ptr<TFile> fFile;

   /// Constructed by Open etc.
   TFilePtr(std::shared_ptr<TFile> &&);

   friend class TFile;

public:
   /// Dereference the file pointer, giving access to the TFileImplBase object.
   TFile *operator->() { return fFile.get(); }

   /// Dereference the file pointer, giving access to the TFileImplBase object.
   /// const overload.
   const TFile *operator->() const { return fFile.get(); }

   /// Check the validity of the file pointer.
   operator bool() const { return fFile.get(); }
};

} // namespace Experimental
} // namespace ROOT
#endif