CODEWITHSUNDEEP
delphi
Fabio Vitale
Fabio Vitale

Reputation: 2287

What is a better method to suspend program execution until a condition is met?

I need to wait until a mapped network folder (\HostName\NetworkPath) become empty. What I mean is that program flow cannot continue until that network folder is empty.

So far I have the following logic in place but I noticed that it takes time before FindFirst notices that the network folder become empty.

If I keep observing an opened explorer windows, pointing to that network folder, I notice that it become empty far before FindFirst notices it.

I used Sleep(5000) to introduce some delay in calling again CheckNetworkFolderIsEmpty in my while loop, otherwise it is being called too often. But maybe that folder will become empty far before 5 seconds, so 5 seconds is an arbitrary time delay that may results in an unnecessary dealy in program execution, in the event that the folder become empty before.

What can be the culprit, what can be a better alternative?

Also I do not know what else to use instead of a simple Sleep.

while not CheckRawFolderIsEmpty do begin
    Sleep(5000);
end;

function TForm1.CheckNetworkFolderIsEmpty: Boolean;
begin
    Result := (CountFilesInFolder('\\HostName\NetworkPath', '*.txt') = 0);
end;

function CountFilesInFolder(const aPath, aFileMask: string): Integer;
var
    Path: string;
    SearchRec: TSearchRec;
begin
    Path := IncludeTrailingPathDelimiter(aPath);
    Result := 0;
    if FindFirst(Path + aFileMask, faAnyFile and not faDirectory, SearchRec) = 0 then begin
        repeat
            Inc(Result);
        until FindNext(SearchRec) <> 0;
        FindClose(SearchRec);
    end;
end;

Upvotes: 2

Views: 189

Answers (1)

Peter Wolf
Peter Wolf

Reputation: 3830

Observing file system changes like you do is inefficient (FindFirst, FindNext) and inacurate as you've learned. Windows provides API FindFirstChangeNotification for that purpose as J... has pointed out in the comment under your question.

Good news is that you don't need to start studying the API from scratch, because some other people did the hard work for you. Check out some freeware wrappers for Delphi around the API:

Upvotes: 4

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