X-Recipient: archive-cygwin AT delorie DOT com
X-Original-To: cygwin AT cygwin DOT com
Delivered-To: cygwin AT cygwin DOT com
X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed;
 d=1e100.net; s=20161025;
 h=x-gm-message-state:subject:to:references:from:message-id:date
 :user-agent:mime-version:in-reply-to:content-transfer-encoding
 :content-language;
 bh=CfTnOrbfuSQpNDO5FCcT+IH0ZdjX9bFsfdsNEwQ/Vkg=;
 b=frZjh6WIvXZwtnLykVO5P5mCrAkX3ICosveS+5MS1C2k0qbFwvroioUibpiG3VosRc
 9sudhHipSnKF4BPekzhVJlH90HInXvq6OOG9hNYhUB0rzyEsxXfAXMFCDsZCNPK+BSXG
 8br/qcRxmh5u8BZuZPe0u3NSwxcEggFHjW8AOYphta3W5HQIucNFyUuk4RdlitKxIB6Y
 9+RykfGZsY9qehvkWFmyAbjPoIDZ8LvZYCSyEy5zDVlmzXV6WCO+TqX4o6Weo2qfBuYs
 58+TABE8Uo4XhMEGTkP42HpXtFJ6s5cWrjMp1ILHoJy0/EnVMMG4XMEsbS1YCQSdJPv0
 aocA==
X-Gm-Message-State: ANhLgQ2jotJ7UHQZ1C0ZJzL1xP1/TgUzGxHlz6F9ogXAQimVm0/+Nr2V
 ajHKueD5I5N4jWOfkTbHfIGWhvavAog=
X-Google-Smtp-Source: ADFU+vufw1kD5pu1lWs4OnOtgFugs0hjX8VF1I8L7VMoVJL02GWhGxuL8lYCelxeqXcZLbhktMmHiQ==
X-Received: by 2002:a2e:854e:: with SMTP id u14mr5722747ljj.27.1584032650585; 
 Thu, 12 Mar 2020 10:04:10 -0700 (PDT)
Subject: Re: Setting termios VMIN > 0 and VTIME > 0 on non blocking file
To: cygwin AT cygwin DOT com
References: <9e4c6428-59de-df07-9e33-44ba95d5497f AT gmail DOT com>
 <20200312114041 DOT GJ4042 AT calimero DOT vinschen DOT de>
 <365dd437-7553-eb4e-3253-aba3bab74895 AT gmail DOT com>
 <20200312144445 DOT GP4042 AT calimero DOT vinschen DOT de>
 <20200312150833 DOT GQ4042 AT calimero DOT vinschen DOT de>
Message-ID: <9e56e005-660b-373e-d557-9c8bc97c45ba@gmail.com>
Date: Thu, 12 Mar 2020 18:04:05 +0100
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:68.0) Gecko/20100101
 Thunderbird/68.5.0
MIME-Version: 1.0
In-Reply-To: <20200312150833.GQ4042@calimero.vinschen.de>
Content-Language: en-US
X-Spam-Status: No, score=-24.6 required=5.0 tests=BAYES_00, DKIM_SIGNED,
 DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, FREEMAIL_FROM, GARBLED_BODY,
 GIT_PATCH_0, GIT_PATCH_1, GIT_PATCH_2, GIT_PATCH_3, RCVD_IN_DNSWL_NONE,
 SPF_HELO_NONE, SPF_PASS autolearn=ham autolearn_force=no version=3.4.2
X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on
 server2.sourceware.org
X-BeenThere: cygwin AT cygwin DOT com
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: Cygwin mailing list <cygwin.cygwin.com>
List-Unsubscribe: <http://cygwin.com/mailman/options/cygwin>,
 <mailto:cygwin-request AT cygwin DOT com?subject=unsubscribe>
List-Archive: <http://cygwin.com/pipermail/cygwin/>
List-Post: <mailto:cygwin AT cygwin DOT com>
List-Help: <mailto:cygwin-request AT cygwin DOT com?subject=help>
List-Subscribe: <http://cygwin.com/mailman/listinfo/cygwin>,
 <mailto:cygwin-request AT cygwin DOT com?subject=subscribe>
From: =?utf-8?q?=C3=85ke_Rehnman_via_Cygwin?= <cygwin AT cygwin DOT com>
Reply-To: =?UTF-8?Q?=c3=85ke_Rehnman?= <ake DOT rehnman AT gmail DOT com>
Content-Type: text/plain; charset="windows-1252"; Format="flowed"
Errors-To: cygwin-bounces AT cygwin DOT com
Sender: "Cygwin" <cygwin-bounces AT cygwin DOT com>
Content-Transfer-Encoding: 8bit
X-MIME-Autoconverted: from quoted-printable to 8bit by delorie.com id 02CH4ehm005056


On 2020-03-12 16:08, Corinna Vinschen wrote:
> On Mar 12 15:44, Corinna Vinschen wrote:
>> On Mar 12 15:20, Åke Rehnman via Cygwin wrote:
>>> I think the problem is if the number of bytes requested are more than what
>> To clarify: number of bytes == VMIN?
no number of bytes requested from ReadFile(). As far as I know Win32 has 
no concept of VMIN.
>>
>>> is in the buffer it is going to overlap the read function (because of VTIME)
>>> and immediately after that CancelIO is called. Contrary to what is mentioned
>>> in the source code I think CancelIO is actually discarding data...
>> So far we didn't have that experience.  CancelIO is usually safe
>> in this regard.
The data is MIA somehow...
>>
>>>    /* Use CancelIo rather than PurgeComm (PURGE_RXABORT) since
>>>           PurgeComm apparently discards in-flight bytes while CancelIo
>>>           only stops the overlapped IO routine. */
>>>
>>>
>>> My suggestion is the following patch:
>>>
>>> diff --git a/winsup/cygwin/fhandler_serial.cc
>>> b/winsup/cygwin/fhandler_serial.cc
>>> index 69e5768f6..afa8871bf 100644
>>> --- a/winsup/cygwin/fhandler_serial.cc
>>> +++ b/winsup/cygwin/fhandler_serial.cc
>>> @@ -898,7 +898,11 @@ fhandler_serial::tcsetattr (int action, const struct
>>> termios *t)
>>>     {
>>>       memset (&to, 0, sizeof (to));
>>>
>>> -    if ((vmin_ > 0) && (vtime_ == 0))
>>> +       if (is_nonblocking())
>>> +       {
>>> +               to.ReadIntervalTimeout = MAXDWORD;
>>> +       }
>>> +    else if ((vmin_ > 0) && (vtime_ == 0))
>> What if you switch to !O_NONBLOCK after calling tcsetattr?  The
>> setting of ReadIntervalTimeout would be lost then.
>>
>> Either we have to repeat calling SetCommTimeouts every time
>> we switch mode, or we have to do the above setting temporary
>> every time we call ReadFile in non blocking mode.
True.
> What about this:
>
> diff --git a/winsup/cygwin/fhandler_serial.cc b/winsup/cygwin/fhandler_serial.cc
> --- a/winsup/cygwin/fhandler_serial.cc
> +++ b/winsup/cygwin/fhandler_serial.cc
> @@ -68,6 +68,16 @@ fhandler_serial::raw_read (void *ptr, size_t& ulen)
>   	goto err;
>         else if (ev)
>   	termios_printf ("error detected %x", ev);
> +      else if (is_nonblocking ())
> +	{
> +	  if (!st.cbInQue)
> +	    {
> +	      tot = -1;
> +	      set_errno (EAGAIN);
> +	      goto out;
> +	    }
> +	  inq = st.cbInQue;
> +	}
>         else if (st.cbInQue && !vtime_)
>   	inq = st.cbInQue;
>         else if (!is_nonblocking () && !overlapped_armed)

Looks promising. I will try it.

BTW there is a gremlin in the "else if (ev)" line....

/Ake

--
Problem reports:       http://cygwin.com/problems.html
FAQ:                   http://cygwin.com/faq/
Documentation:         http://cygwin.com/docs.html
Unsubscribe info:      http://cygwin.com/ml/#unsubscribe-simple