fmShareDenyNone
fmShareDenyNone = 64
Example
function OpenForConcurrentRead(const FileName: String): TFileStream;
begin
Result := TFileStream.Create(FileName, fmOpenRead or fmShareDenyNone);
end;
Usage
fmShareDenyNone allows compatible competing readers and writers while a file handle is open, without providing atomicity or content stability.
Additional Technical Info
fmShareDenyNone requests that compatible competing opens be allowed for both reading and writing. In the current Windows RTL, the resulting handle passes FILE_SHARE_READ or FILE_SHARE_WRITE to the operating system.
This is the most permissive exposed share mode. It is useful when external processes must continue updating or replacing a file, but it provides no stable snapshot: Size and content can change between or during reads, and interleaved writers can overwrite each other. A successful open does not make a later multi-step operation atomic.
Share flags are evaluated against other handles' requested access and sharing. They do not override permissions, make non-cooperating access safe, lock in a path target, prevent rename/delete behavior on every platform, or remove check/open races. Free the stream promptly so the handle does not outlive the intended operation.
OR this value with exactly one existing-file access mode. It cannot make fmCreate permissive in Velox because the script's legacy $FFFF create value already has every share bit set and is remapped to exclusive.
The example returns an owned stream and is source-reviewed only; no file was opened.
External references
Created 2026-07-15