Memory mapping on file expires?

Question

I have a file on which I use memory mapping to create huge array (which may not fit in physical memory). There are two areas mapped on memory - array count (4 bytes) and some window which is moving on file to get access to different elements of array.

Everything works fine, unless one problem. After some multiple operations with array count (sometimes millions of operations) - I get system message "Access denied" when I am trying to read or write this count by its memory address which never changes since its creation.

It looks like this mapped page expires in some way...

    type
      // view info
      TViewInfo = record
        ptr: pointer;                      // pointer to fist byte in view
        offset: longword;                  // offset of our data inside the view
        addr: PPointer;                    // pointer to variable pointer (ptr + offset)
      end;

      TSizeRec = packed record
      case integer of
        0: (full: int64);
        1: (lo, hi: longword);
      end;


    function TFileMappedArray.CreateView(offset: int64; size: longword; var p: pointer): TViewInfo;
    var
      offs: TSizeRec;
      fsize: int64;
    begin
      p := nil;
      result.addr := @p;

      // view must start on the mem_granularity*N offset
      // so we need to adjust our numbers
      result.offset := offset mod fMemGranularity;
      offs.full := (offset div fMemGranularity)*fMemGranularity;
      size := size + result.offset;

      fsize := int64(fMaxNumOfItems)*fItemSize + sizeof(longword);
      if (offs.full  fsize) then
        size := fsize - offs.full;

      result.ptr := MapViewOfFile(fMappingHandle, FILE_MAP_WRITE, offs.hi, offs.lo, size);

      p := pointer(longword(result.ptr) + result.offset);
    end;


    var
      fNumberOfItems: PLongword;   // our counter
      fNumberView: TViewInfo;      // our view


    // create view of first 4 bytes in file
    fNumberView := CreateView(0, 4, pointer(fNumberOfItems));


    // get count
    array count := fNuberOfItems^;

    // set count
    fNumberOfItems^ := new count;

get or set count produces error sometimes, randomly and very rarely

Answer 1

There was mistake in releasing file handle after creating memory mapping. No expiration over time. But you should keep file handle as long as memory mapping exists.