[fpc-pascal] TProcess does not work in Windows XP
Michael Van Canneyt
michael at freepascal.org
Wed Mar 25 09:54:05 CET 2015
On Wed, 25 Mar 2015, Antonio Sanguigni wrote:
> 2015-03-25 8:41 GMT+01:00 Michael Van Canneyt <michael at freepascal.org>:
>>> ---------------------- code ---------------
>>> procedure TBurpClient.Run;
>>> fOurProcess.Options := [poUsePipes] + [poNoConsole];
>>> while True do
>>> // make sure we have room
>>> fMemStream.SetSize(fBytesRead + READ_BYTES);
>>> // try reading it
>>> fNumBytes := fOurProcess.Output.Read((fMemStream.Memory +
>>> fBytesRead)^, READ_BYTES);
>>> if fNumBytes > 0 then // All read() calls will block, except the final
>> I am not sure this is always correct. Various versions of windows work
>> differently in this regard;
>> zero (0) may be a valid return value. I suggest you check
>> fOurProcess.IsRunning to break the loop.
> Thank you, I will try it. But debugging I can see the problem is not
> in the loop. In Windows XP fNumBytes is always zero:
> fNumBytes := fOurProcess.Output.Read((fMemStream.Memory +
> fBytesRead)^, READ_BYTES);
> so it seems the Read of fOurProcess.Output is not giving the expected results.
Read translates directly to a kernel call.
> In Windows 7 it's ok.
Zero is a valid return value for read from a pipe.
So it can perfectly be that read attempts 50 times returns 0, and only at
read attempt 51 you get a positive result.
That is why you must check isRunning, and not rely on the return value of readbytes.
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