DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 019CA3858D38
Message-ID: <58359837-fd07-50a0-d5f8-b07bf425b7df@cornell.edu>
Date: Tue, 20 Sep 2022 09:18:01 -0400
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101
 Thunderbird/102.2.2
Subject: Re: FIFO issues
Content-Language: en-US
To: cygwin AT cygwin DOT com
References: <a3084ca6-ea7b-535c-c0fb-2c29e20b7ddb AT cornell DOT edu>
 <1b28b650-b588-e34f-919e-e75f5a01196f AT lyx DOT org>
 <9e531437-9e27-969f-517e-ec5607212c76 AT cornell DOT edu> <YyljrduQ+ljG6OOa AT GIOVE>
From: Ken Brown <kbrown AT cornell DOT edu>
In-Reply-To: <YyljrduQ+ljG6OOa@GIOVE>
MIME-Version: 1.0
X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1
X-MS-Exchange-AntiSpam-MessageData-0: =?utf-8?B?eitFc1Z0cjZJMWJhaVlpNERUcmxyN0JndkYyNlA5cGJ3eFNjejFNRHNkTUp3?=
 =?utf-8?B?REhvaDkxbEFFVENwSmhCV0ZKOXI0TlRaRFF3VWZBbEQrOVI1U1F3Z09hVHB1?=
 =?utf-8?B?UkxZakJnU2V3OEdBWUNlOTdwcEtoTStCQ1M4UmJzZklCRWIvSkFQTWdrZG5q?=
 =?utf-8?B?cUZJV2JQN3VOcTdtMlVKeG9POVM2Q2xhbnlJSTVMSVUwWnc3djU4cWlZay9o?=
 =?utf-8?B?dHdXaVlFak9kWndHSVRYM2tYb3ZmNFN5SmFxb2dPZVFxTWgyNzR6MFlpa2Ni?=
 =?utf-8?B?YTBJWDd3ZjN3YXR1RTUyZFB1eDJkUkMvckxIeXhSYVBLTkUzd042MWFZbWIz?=
 =?utf-8?B?ejhqcllvWCtRU3k3THFPV3UvdW01ZWVqQkRDRXNLa1ZaN3ZOYkl6ZG53ZkVX?=
 =?utf-8?B?UjU4SjJubWVLMHMzTTVSZDcxTnA1eDJqUWY3VFRBczNwZ2FvK1BEVzlNT0dn?=
 =?utf-8?B?ek5LbkRvcm9jQ3Y4TmllVld3bEV6OVV2dHlCaWxLaXRoT3l2WkFjazR4R2xm?=
 =?utf-8?B?dndqWVVjMGwzRDMwcWJSZkFFVTFQMFdPOUVNTjBraVJPNlB2VEwrZ2xXUlF6?=
 =?utf-8?B?QjlyOUZQdDJZb2N2UkhHSVcvS2pkSzRrSEl1VkQwL0lqdmlJYlZPVzF0T3Jj?=
 =?utf-8?B?cXh0dVhlT01NWHVuelNWbVZPaVNVaytHYkorQ0Z4UUpJdnFuc2l4akRoV0VV?=
 =?utf-8?B?WGw3Q2lDV0ZtWlliTjdjVzhLWVByYm1Cd0VKSXQxVFF1VG1HSmdRQ1ZUSm12?=
 =?utf-8?B?Y1Z6WmNsYStvQzYrazlBTGVpeGVUZFdHUlZyODRYQUtrd21zUk9QVzRmUkgz?=
 =?utf-8?B?WFFjRzJhUkw1UGxHMXp0TDNBdFA3VzZxUE9FaDJIY0E1K1BuQWppVUlHa2Vr?=
 =?utf-8?B?czJ5SUZ1bml5RUQ2UlBUV0J0bnFmTkFrb1hqRnUvMHRIUXpaY1pQK0NzT1Vz?=
 =?utf-8?B?aUdwSytqVzRGMTlIOW5rdjNPZUdjcWRGTjZ6L0xlaFZ6RXVwUnp6c01SY1Qz?=
 =?utf-8?B?MEZiYmNxd0M2d3N2ZE1jQkRra3l6b1lDeGM1Wis1UFBGRGJCQ2JTMnpzZTM2?=
 =?utf-8?B?cWwvc1FtNmJNUGVpT2NXSmx4alNaeWxJSHc1aWN1bzFzQmx0SXJWakhVQ0JR?=
 =?utf-8?B?SkRYWWdUM05zSkNxRS9rdDMySlV0Vm9rRWNRbUlEd2lPT2dJVk1IRWlsVjZD?=
 =?utf-8?B?SkZpcUc5OVJ5SDg1SGxUOTY1cEJ4aXU4ZGh5TUFsSStETEI5Q295VG04OUVj?=
 =?utf-8?B?TTJuSWZEd1Jna0hFUmJQaFhUdWU1K2pic1R2Ym9oWUVmd1dlRVMvY0ZRVk1P?=
 =?utf-8?B?bHJnYS82S2lud1dQOFQrT25JSWVMSVNQNVA3ampjcmVmR1g3M0hVams1ODBy?=
 =?utf-8?B?V21KRG5sMnNkQTJqUzhpMVNsZm0zT0lXZi9BUGRaMk9DTzRZMEhOZ05FWVJr?=
 =?utf-8?B?Z01ZSC9lbGkwRTRRL0o0NnNRYm5LRk85NStXZWVsSjBxcEk2TVhQY2d5eTQ1?=
 =?utf-8?B?NFJEVlBsZTVMT0EzUXBvQ0FOdWJXdmpBWTVWWFpwQnRjWEtJM0RZVmpOdlI0?=
 =?utf-8?B?c0RsU1hKK1ZrOUVsVjRrZE10UGNSeUhHdE5aTXNRYVdQWHVRZnVKdDFUOUw1?=
 =?utf-8?B?SzJRYS9NdThHUHFDOHJ5eDkwb3NsMjlJRUdkYWpVblhlVktYUy9jc3plMm9x?=
 =?utf-8?B?bElKazl4YUhsSEw5YW92UjRBVzVGSHQ4ZHlPNnVudE5tRHJ6bE1VOXQ0dS9i?=
 =?utf-8?B?ckdldDFuRW0yNjF2ZlI2WXVpVXhEYnVmN01mM1o5b2JNcGVxejBTZVErOWxM?=
 =?utf-8?B?T3cyYWdCY21wR1hWclUxTDJFK1hVaGhtdUpMcnlnc1pvUWdQS0dPV0ZpOUkz?=
 =?utf-8?B?OERWNTREVmhsTWpiamJNV0hpSEoyZ0tMZG8yWWdYS2JOa05VVlZIN2ZSZ01Y?=
 =?utf-8?B?RXpwbTAvaXlsQ3JubW5Sc09YQnlVR1FIRk5ZZjFGMjRqc0Q2Z2kwd1p5NEhS?=
 =?utf-8?B?dXlGdm9BdDVaZlQ4OE9YNzZrTko1VW1yOExWTE0zbkJ6bjZkWWxPRVdCQi9m?=
 =?utf-8?B?bGxIai9YTzBXaElObmQ4dUM2cUlnZk1ic3BEN1BvYVRtUFV0NVVJcGNYU3Iw?=
 =?utf-8?B?ZCtwOTdBSEp0eCtidytrcy9SbkY2SVdhVHVtTnVsK2FPS2pubXBJMjBOUEsr?=
 =?utf-8?Q?tkd7LrPapbUFpK7DHdcWoKJIwpAllu+UXLn4RezyIIiS?=
X-OriginatorOrg: cornell.edu
X-MS-Exchange-CrossTenant-Network-Message-Id: 84a3aaac-2483-44fd-c40f-08da9b0a8c89
X-MS-Exchange-CrossTenant-AuthSource: SA0PR04MB7322.namprd04.prod.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Internal
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 20 Sep 2022 13:18:03.8194 (UTC)
X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted
X-MS-Exchange-CrossTenant-Id: 5d7e4366-1b9b-45cf-8e79-b14b27df46e1
X-MS-Exchange-CrossTenant-MailboxType: HOSTED
X-MS-Exchange-CrossTenant-UserPrincipalName: ODUqfAqT7MzY37wBs45PFJLCR3KIYDwQYi9JFy3AXZFoxTtM221Ta9emcxYdnkLTJYNCdaux68QfE1Wt+dCSBg==
X-MS-Exchange-Transport-CrossTenantHeadersStamped: MWHPR04MB1104
X-Spam-Status: No, score=-4.0 required=5.0 tests=BAYES_00, DKIM_SIGNED,
 DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, JMQ_SPF_NEUTRAL, NICE_REPLY_A,
 RCVD_IN_DNSWL_NONE, RCVD_IN_MSPIKE_H2, SPF_HELO_PASS, SPF_PASS,
 TXREP autolearn=ham autolearn_force=no version=3.4.6
X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on
 server2.sourceware.org
X-BeenThere: cygwin AT cygwin DOT com
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: General Cygwin discussions and problem reports <cygwin.cygwin.com>
List-Unsubscribe: <https://cygwin.com/mailman/options/cygwin>,
 <mailto:cygwin-request AT cygwin DOT com?subject=unsubscribe>
List-Archive: <https://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: <https://cygwin.com/mailman/listinfo/cygwin>,
 <mailto:cygwin-request AT cygwin DOT com?subject=subscribe>
Content-Transfer-Encoding: 7bit
Content-Type: text/plain; charset="us-ascii"; Format="flowed"
Errors-To: cygwin-bounces+archive-cygwin=delorie DOT com AT cygwin DOT com
Sender: "Cygwin" <cygwin-bounces+archive-cygwin=delorie DOT com AT cygwin DOT com>

On 9/20/2022 2:54 AM, Enrico Forestieri wrote:
> On Mon, Sep 19, 2022 at 07:54:11PM -0400, Ken Brown wrote:
>> Then I guess I'm wrong.  I'm really puzzled, because it seems that none of these
>> platforms agree with POSIX, which says the following in its 'read' documentation:
>>
>>       When attempting to read from an empty pipe or FIFO:
>>
>>           If no process has the pipe open for writing, read() shall return 0 to
>>           indicate end-of-file.
>>
>> It seems that there's an exception: If no process has ever had the FIFO open for
>> writing since it was opened for reading, then the FIFO is not considered to be
>> at end-of-file.
>>
>> I'll look into fixing this.  But I'd be more confident about it if I could find
>> some documentation of the existing behavior.
> 
> I compared the behavior of read() and select() on 3 different platforms.
> My conclusion is that, actually, read() behaves the same on all of them,
> whereas cygwin differs in the way select() works.

Then I'm even more confused than I was before.  Are you saying that there are 
situations in which read() reports EOF but select() does not report read ready? 
Could you post the code you used for testing?

Thanks.

Ken

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