Warrior_EA/System/AtomicFile.mqh

//+------------------------------------------------------------------+
//|                                                       Warrior_EA |
//|                                                     AnimateDread |
//|                                                                  |
//| Crash-safe binary file writes.                                   |
//+------------------------------------------------------------------+
#ifndef WARRIOR_ATOMIC_FILE_MQH
#define WARRIOR_ATOMIC_FILE_MQH

//+------------------------------------------------------------------+
//| Open a temp file to stage an atomic binary write.                |
//+------------------------------------------------------------------+
int AtomicWriteBegin(const string finalName, const int commonFlag, string &tmpName)
  {
   tmpName = finalName + ".savetmp";
   ResetLastError();
   return FileOpen(tmpName, commonFlag | FILE_BIN | FILE_WRITE | FILE_SHARE_READ | FILE_SHARE_WRITE);
  }

//+------------------------------------------------------------------+
//| Close the staged write and either publish it or discard it.      |
//+------------------------------------------------------------------+
bool AtomicWriteEnd(const int handle, const string finalName, const string tmpName,
                    const int commonFlag, const bool ok, const string context)
  {
   if(handle != INVALID_HANDLE)
     {
      FileFlush(handle);
      FileClose(handle);
     }
//--- A failed/partial write must NEVER touch the real file - discard the temp, keep the last good copy.
   if(!ok)
     {
      FileDelete(tmpName, commonFlag);
      Print(context, ": write to ", tmpName, " failed - kept the existing ", finalName,
            " intact (no atomic swap performed)");
      return false;
     }
//--- Atomic swap: FILE_REWRITE lets FileMove replace an existing destination in one operation.
   ResetLastError();
   if(!FileMove(tmpName, commonFlag, finalName, commonFlag | FILE_REWRITE))
     {
      Print(context, ": atomic rename ", tmpName, " -> ", finalName, " failed (error ",
            IntegerToString(GetLastError()), ") - the temp holds the new content and the existing ",
            finalName, " is unchanged");
      ResetLastError();
      return false;
     }
   return true;
  }
//+------------------------------------------------------------------+
#endif // WARRIOR_ATOMIC_FILE_MQH