🚀 go-pugleaf

> You removed some code. Did any of that code contain CancelIO() ?

No.

> You didn't show osRead or osWrite.

Here is (a simplified version of) the class definition:

class TCustomCOMPort : public TComponent
{
  friend TCOMStatThread;

  private:
    TCOMStatThread *StatThread;
    OVERLAPPED  osRead;
    OVERLAPPED  osWrite;

    TCOMDataEvent FOnDataAvailable;
    TCOMErrorEvent FOnError;

    void __fastcall WaitForAsync (OVERLAPPED &Overlapped, DWORD &ByteCount);

  protected:
    bool __fastcall Open ();
    bool __fastcall Close ();
    DWORD __fastcall Read (void *Buffer, DWORD Size);
    DWORD __fastcall Write (void *Buffer, DWORD Size);

    __property TCOMDataEvent OnDataAvailable = {read=FOnDataAvailable,
write=FOnDataAvailable};
    __property TCOMErrorEvent OnError = {read=FOnError, write=FOnError};

  public:
    __fastcall TCustomCOMPort (TComponent *Owner);
    __fastcall ~TCustomCOMPort ();
};

The thread is created in the Open() method and destroyed in the Close()
thread, which means that the thread runs as long as the COM port is open.

> Your class has One OVERLAPPED struct, not 2, and you wait on 2 events.

My class has 1 OVERLAPPED struct (for WaitCommEvent) and 1 event for
signalling thread termination (doesn't require an OVERLAPPED struct).

> I would think you would want to wait on 3 events, evRead, evWrite and
> evTerminate

In TCOMStatThread? Reading and writing is handled in TCustomCOMPort. I don't
need reading/writing in the background, which would be done in
TCOMStatThread. Blocking read/write (with timeouts) is all I need. The COM
port component is used for communicating with devices that use a
command/reply communication model (the PC sends a request and waits for a
reply from the device).

> You are blocking after read and write, so why are you using overlapped
> instead of blocking i/o?

Non-overlapped I/O doesn't work in WinXP.

> You aren't handling any errors from ReadFile() or WriteFile().

Can you tell me which errors to handle and how to handle them?

Thanks for your reply.

Martin