Indy : Object[i].delete method can't free memory? - delphi

Question

This is my simple code for queue[i] freeing memory ...
Is it correct?
The monitor is a customized TIdContext object.
...
var queue : TList;
...
queue := monitor.Screenshots.LockList;
if queue.Count > 0 then
begin
for i := 0 to queue.Count - 1 do
begin
if TScreenshotInfo(queue[i]).ClientIP = request_AgentIP then
begin
screenshot := TScreenshotInfo(queue[i]);
end;
queue.Delete(i);//Can't free queue[i] from memory?
end;
end;
...

Answer 1

queue := monitor.Screenshots.LockList;
try
for queue.Count-1 downto 0 do begin
if TScreenshotInfo(queue[i]).ClientIP = request_AgentIP then
TScreenshotInfo(queue[i]).Free;//queue[i] freed
queue.Delete(i);
end;
finally
monitor.Screenshots.UnlockList;
end;
I assume there's some reason why an item is deleted and not freed if it doesn't match the condition.

Answer 2

As I already explained in comments to your other question on this same issue:
You have memory leaks in IdTCPServer_SendExecute(). IdTCPServer_RecvExecute() queues a screenshot to all connected monitors, but IdTCPServer_SendExecute() only processes screenshots from a specific client, discarding all other client screenshots from the queue without freeing them from memory. Also, if multiple screenshots from the desired client are in the queue, you only process the last screenshot, discarding the earlier screenshots without freeing them. In short, your loop processing in IdTCPServer_SendExecute() has logic holes in it.
The code needs to look more like this:
destructor TMonitorContext.Destroy;
var
queue: TList;
i: Integer;
begin
queue := Screenshots.LockList;
try
for i := 0 to queue.Count - 1 do begin
TScreenshotInfo(queue[i]).Free;
end;
finally
Screenshots.UnlockList;
end;
Screenshots.Free;
CloseHandle(ScreenshotEvent);
inherited;
end;
procedure TIndyServerForm.IdTCPServer_SendExecute(AContext: TIdContext);
var
monitor: TMonitorContext;
queue: TList;
screenshot: TScreenshotInfo;
request_AgentIP: string;
begin
monitor := TMonitorContext(AContext);
if WaitForSingleObject(monitor.ScreenshotEvent, 1000) <> WAIT_OBJECT_0 then begin
Exit;
end;
// you really should not be requesting an IP on every screenshot sent.
// request an IP once at connection, and don't request a new IP unless
// you want to monitor a different client. This is especially useful
// for allowing IdTCPServer_Recv to not queue screenshots this monitor
// is not interested in receiving...
request_AgentIP := AContext.Connection.IOHandler.ReadLn;
screenshot := nil;
try
queue := monitor.Screenshots.LockList;
try
while queue.Count > 0 do
begin
screenshot := TScreenshotInfo(queue[0]);
queue.Delete(0);
if screenshot.ClientIP = request_AgentIP then
Break;
end;
FreeAndNil(screenshot);
end;
if queue.Count = 0 then
ResetEvent(monitor.ScreenshotEvent);
finally
monitor.Screenshots.UnlockList;
end;
if screenshot = nil then begin
Exit;
end;
// you should send screenshot.ClientIP and screenshot.ClientPort to
// this monitor so it knows which client the screenshot came from...
if not SendStream(AContext, screenshot.Data) then
begin
SOutMsg :='viewer : ' + AContext.Binding.PeerIP + ': reqIP(' + request_AgentIP + ')-> image send failed : ' + KBStr(screenshot.Data.Size) +' #'+TimeToStr(Now);
AContext.Connection.Disconnect;
end
else
begin
SOutMsg :='viewer : ' + AContext.Binding.PeerIP + ': reqIP(' + request_AgentIP + ')-> image send success : ' + KBStr(screenshot.Data.Size)+' #'+TimeToStr(Now);
end;
finally
screenshot.Free;
end;
end;