Warrior_EA/System/AtomicFile.mqh

//+------------------------------------------------------------------+
//|                                                       Warrior_EA |
//|                                                     AnimateDread |
//|                                                                  |
//| Crash-safe file writes: temp file + atomic rename.                |
//+------------------------------------------------------------------+
#ifndef WARRIOR_ATOMIC_FILE_MQH
#define WARRIOR_ATOMIC_FILE_MQH

//--- DEFERRED PROMOTION, and the in-line retry that preceded it was WRONG. A rename fails when a peer
//--- chart holds the destination open, and MQL5 has no FILE_SHARE_DELETE, so the rename simply cannot
//--- succeed for as long as that reader is open. The first attempt at this assumed a reader holds a
//--- pool file for "tens of ms" and spun 4x25ms; measured, `USDCAD_16388.bin` is 134 MB and a peer
//--- reading it holds the handle for SECONDS. The loop lost every time (`failed ... after 4 attempts`)
//--- and all it bought was 75ms of tick latency on the failure path.
//---
//--- So: try ONCE, and if the destination is busy, REMEMBER the temp and promote it from the timer.
//--- The content is already written and correct - only the swap is blocked - so once the reader closes,
//--- a single FileMove lands it. That beats waiting for the next full publish, which would re-write all
//--- 134 MB and might be an era away.
//--- THE STAGING FILE MUST BE PRIVATE TO THE WRITER. It used to be `finalName + ".savetmp"`, derived
//--- from the DESTINATION alone - which is fine for a chart-local file and a genuine data-integrity
//--- bug for a shared one in Common\Files. Several charts fetch the same alt-data series and write
//--- the same destination, so they all opened ONE temp with FILE_WRITE and wrote it from offset 0 at
//--- once; whichever renamed first published whatever mixture of two charts' output the interleaving
//--- happened to leave. Observed 2026-08-26: EURUSD and XTIUSD both failed to rename
//--- `raw_EIA_WPSR.csv` in the SAME MILLISECOND, with a third writer winning the race.
//---
//--- Keying the temp on symbol+period makes staging private: the rename stays the only contended
//--- operation, and a rename is atomic, so a loser now publishes nothing rather than half of itself.
//--- It is also what makes deferred promotion sound - the temp promoted later is THIS chart's
//--- complete content, never a fragment of someone else's.
string AtomicTempName(const string finalName)
  {
   return StringFormat("%s.%s_%d.savetmp", finalName, _Symbol, (int)_Period);
  }

#define ATOMIC_PENDING_MAX 8
string g_atomicPendingFinal[ATOMIC_PENDING_MAX];
int    g_atomicPendingFlag[ATOMIC_PENDING_MAX];
int    g_atomicPendingCount = 0;

//--- Bounded and deduplicated: there is only ever one temp per (final name, THIS chart), because
//--- AtomicTempName() reuses it, so a second failure for the same file must not take a second slot.
void AtomicRememberPending(const string finalName, const int commonFlag)
  {
   for(int i = 0; i < g_atomicPendingCount; i++)
      if(g_atomicPendingFinal[i] == finalName && g_atomicPendingFlag[i] == commonFlag)
         return;
   if(g_atomicPendingCount >= ATOMIC_PENDING_MAX)
      return;                       // full: this one falls back to the next publish, as it always did
   g_atomicPendingFinal[g_atomicPendingCount] = finalName;
   g_atomicPendingFlag[g_atomicPendingCount]  = commonFlag;
   g_atomicPendingCount++;
  }

void AtomicForgetPending(const string finalName, const int commonFlag)
  {
   for(int i = 0; i < g_atomicPendingCount; i++)
      if(g_atomicPendingFinal[i] == finalName && g_atomicPendingFlag[i] == commonFlag)
        {
         g_atomicPendingFinal[i] = g_atomicPendingFinal[g_atomicPendingCount - 1];
         g_atomicPendingFlag[i]  = g_atomicPendingFlag[g_atomicPendingCount - 1];
         g_atomicPendingCount--;
         return;
        }
  }

//--- Called from the TIMER, not the tick: this is I/O, and the whole point is to stop paying for it
//--- inside a quote. Returns how many it managed to land. Cheap when there is nothing pending, which
//--- is the overwhelmingly common case.
int AtomicPromotePending(void)
  {
   int promoted = 0;
   for(int i = g_atomicPendingCount - 1; i >= 0; i--)
     {
      string finalName = g_atomicPendingFinal[i];
      string tmpName   = AtomicTempName(finalName);
      int    flag      = g_atomicPendingFlag[i];
      //--- Gone means someone else already resolved it (a later publish succeeded outright). Drop it.
      if(!FileIsExist(tmpName, flag))
        {
         AtomicForgetPending(finalName, flag);
         continue;
        }
      ResetLastError();
      if(!FileMove(tmpName, flag, finalName, flag | FILE_REWRITE))
         continue;                  // still held; try again on the next timer
      Print("Warrior: deferred promotion of ", finalName, " succeeded - the peer chart that held it"
            " has closed it, and the content written earlier is now live without rewriting the file.");
      AtomicForgetPending(finalName, flag);
      promoted++;
     }
   return promoted;
  }

//+------------------------------------------------------------------+
//| Open a temp file to stage an atomic write. modeFlags defaults to |
//| FILE_BIN (every original caller wrote binary payloads); a text   |
//| writer passes FILE_TXT|FILE_ANSI so FileWriteString still emits  |
//| plain lines instead of length-prefixed binary records.           |
//+------------------------------------------------------------------+
int AtomicWriteBegin(const string finalName, const int commonFlag, string &tmpName, const int modeFlags = FILE_BIN)
  {
   tmpName = AtomicTempName(finalName);
   ResetLastError();
   return FileOpen(tmpName, commonFlag | modeFlags | 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.
//---
//--- RETRIED, BECAUSE THE COMMON FAILURE IS TRANSIENT AND NOT OURS. Six charts share the TrainPool
//--- and AltData directories, so a publish regularly lands while a PEER CHART has the destination
//--- open for reading, and the rename comes back 5004 (which MQL5 uses for both "no such file" and
//--- "locked by another process"). Measured 27 times in one day on the live fleet before this loop
//--- existed. Nothing was lost - the temp keeps the new content and the old file stays intact - but
//--- the pool row simply did not update until the next publish, which on a chronically busy
//--- directory could be a long time.
//---
//--- The sleep is on the FAILURE PATH ONLY: a successful rename does not sleep at all, so the common
//--- case costs one extra comparison. Skipped in the tester (where Sleep distorts a pass and the
//--- contention cannot happen - one process, no peers) and when the program is stopping, where
//--- Sleep returns immediately anyway and the remaining attempts should just be spent at once.
   ResetLastError();
   if(FileMove(tmpName, commonFlag, finalName, commonFlag | FILE_REWRITE))
     {
      //--- A fresh write supersedes anything queued for this name.
      AtomicForgetPending(finalName, commonFlag);
      return true;
     }
   int lastErr = GetLastError();
   AtomicRememberPending(finalName, commonFlag);
   Print(context, ": atomic rename ", tmpName, " -> ", finalName, " failed (error ",
         IntegerToString(lastErr), ") - a peer chart is holding it open. The temp holds the new"
         " content and ", finalName, " is unchanged; the timer will promote it as soon as the"
         " reader closes, without rewriting the file.");
   ResetLastError();
   return false;
  }
//+------------------------------------------------------------------+
#endif // WARRIOR_ATOMIC_FILE_MQH