Warrior_EA/System/AtomicFile.mqh

//+------------------------------------------------------------------+
//|                                                       Warrior_EA |
//|                                                     AnimateDread |
//|                                                                  |
//| Crash-safe binary file writes.                                    |
//|                                                                  |
//| WHY THIS EXISTS. FileOpen(FILE_WRITE) TRUNCATES its target the    |
//| instant it opens. Writing straight to the destination therefore   |
//| destroys the previous good copy before the first byte of the new  |
//| one is written, so anything that interrupts the write - a force-  |
//| kill, an OnDeinit that overruns MT5's deinit budget ("Abnormal    |
//| termination"), a full disk - leaves a truncated file behind. On   |
//| the next load that reads as corrupt, and for this EA that has     |
//| meant retraining from era 0.                                      |
//|                                                                  |
//| The fix is to write to a temp file and rename it over the target  |
//| only after a fully successful write. A rename on the same volume  |
//| is atomic: an interrupted save leaves a junk .savetmp and the     |
//| real file stays whole, so a restart always resumes the last       |
//| COMPLETE save.                                                    |
//|                                                                  |
//| It also fixes a second, subtler problem. Windows file sharing is  |
//| a MUTUAL contract: a writer that opens with no FILE_SHARE_* flags |
//| blocks every concurrent open no matter what flags the READER      |
//| passes. Every FileOpen(...FILE_READ...) in this codebase already  |
//| carries FILE_SHARE_READ|FILE_SHARE_WRITE (see CopySharedFile);    |
//| those flags cannot do their job while an exclusive writer holds   |
//| the same path. Writing to a temp path instead means the live      |
//| destination is never held open for writing at all, so concurrent  |
//| readers (tester agent seeding its cache from a live chart's       |
//| model) always succeed - and they can never observe a torn file,   |
//| because the rename publishes it in one step.                      |
//|                                                                  |
//| CNet::Save established this pattern for the .nnw; this header is  |
//| that logic lifted out so the sidecars written next to it (.stats, |
//| .arrows, .cfg) get the identical guarantee instead of each        |
//| re-implementing it - or, as was the case, not implementing it.    |
//+------------------------------------------------------------------+
#ifndef WARRIOR_ATOMIC_FILE_MQH
#define WARRIOR_ATOMIC_FILE_MQH

//+------------------------------------------------------------------+
//| Open a temp file to stage an atomic binary write.                 |
//|                                                                  |
//| finalName  - the real destination, WITHOUT any temp suffix.       |
//| commonFlag - FILE_COMMON, or 0 for this program's own sandbox.    |
//| tmpName    - receives the temp path; pass it back unchanged to    |
//|              AtomicWriteEnd().                                    |
//|                                                                  |
//| Returns a handle opened FILE_BIN|FILE_WRITE, or INVALID_HANDLE.   |
//| Callers must pair every successful call with AtomicWriteEnd().    |
//+------------------------------------------------------------------+
int AtomicWriteBegin(const string finalName, const int commonFlag, string &tmpName)
  {
   tmpName = finalName + ".savetmp";
   ResetLastError();
   return FileOpen(tmpName, commonFlag | FILE_BIN | FILE_WRITE);
  }

//+------------------------------------------------------------------+
//| Close the staged write and either publish it or discard it.       |
//|                                                                  |
//| ok = false discards the temp and leaves the existing destination  |
//| untouched, which is the entire point: a partial write must never  |
//| replace a good file.                                              |
//|                                                                  |
//| `context` is used only for log messages (e.g. "CNet::Save").      |
//| Returns true only when the destination now holds the new content. |
//+------------------------------------------------------------------+
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.
//--- CRITICAL: FileMove's SOURCE location is the 2nd arg (commonFlag); the DESTINATION location is set by
//--- FILE_COMMON *inside the 4th arg* (mode_flags) - it is NOT inherited from the source. Passing only
//--- FILE_REWRITE (a real, previously-shipped bug) moved the temp from Common\Files to LOCAL\Files on a
//--- live chart (common=true): FileMove returned true so no error showed, but the file landed in the
//--- wrong sandbox and the loader (which reads Common) saw "no saved model" -> era 0 every restart.
//--- commonFlag MUST be OR'd into the destination flags so source and destination are the same location.
   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