X-Recipient:	archive-cygwin AT delorie DOT com
DKIM-Filter:	OpenDKIM Filter v2.11.0 sourceware.org A157D385B513
DKIM-Signature:	v=1; a=rsa-sha256; c=relaxed/relaxed; d=cygwin.com;
	s=default; t=1676559595;
	bh=vhTTOZQy5DuciuObbbLWxoB4o4syP2TFELZMkrNj8Eg=;
	h=Date:To:Subject:References:In-Reply-To:List-Id:List-Unsubscribe:
	List-Archive:List-Post:List-Help:List-Subscribe:From:Reply-To:Cc:
	From;
	b=EJjnoBVoS2Re2uhXEKUo2r35XMHspYDcjmTvAaw85Ar/rBjGWh74ciSVhwpaw+kNY
	XPjqETfnHF81PrlK7R/qRN7NHy/kCXNX2BzSJqpOa/tfpUqTmdEviVO3K7egYshpJe
	7khKEgsnFZlzlFZiLc0Qh+NmpH5AjxnUSlpWdDco=
X-Original-To:	cygwin AT cygwin DOT com
Delivered-To:	cygwin AT cygwin DOT com
Date:	Thu, 16 Feb 2023 15:59:36 +0100
To:	Yeo Kai Wei <yeokaiwei AT hotmail DOT com>
Subject:	Re: [QUERY] Help With Semaphore Error on Windows : Cygwin
Message-ID:	<Y+5E2Hftco5JMrpl@calimero.vinschen.de>
Mail-Followup-To:	Yeo Kai Wei <yeokaiwei AT hotmail DOT com>, cygwin AT cygwin DOT com
References:	<PH0PR05MB9918C60D1BF4A9A8D25DEADEA4A09 AT PH0PR05MB9918 DOT namprd05 DOT prod DOT outlook DOT com>
MIME-Version:	1.0
In-Reply-To:	<PH0PR05MB9918C60D1BF4A9A8D25DEADEA4A09@PH0PR05MB9918.namprd05.prod.outlook.com>
X-Provags-ID:	V03:K1:c0OBZENpvnD8inteaGj1EeJQ067jwcaArRAEjKyRcJFa4qq85re
	Caf+8QT3ItyLyGMLUpWQCfAQ9wCbFNHYvLWWZ3PyOgytPAC0XkBucdB4YEr5JVONYG7ioJw
	wPTfcJBjuBZOxIuYbZycumnz2+A96sFBl5M8XHnP1hkd0kCyU7aFFVQiPsv4nyNkm+h+k9h
	Xex8gF2Z/yknmEZldRI3A==
UI-OutboundReport:	notjunk:1;M01:P0:AO3lHMIcZBw=;F89DVsy6Swf3yeqgsI9NOTMki6c
	1cRvq0Ht6WgxTysFXNCNixJH5/9WGQHdjkrbhXaJRJJyRoIFPQhK+Pw/wKuCLj34NkbQbIS1h
	TPqo3WERJ6/ZcIkdJqq9rNoEWX8tqcR5+1zHx4qe9qewdvU3RMIumkEiN+NbFGBsymmssJdIk
	1X4o61uy8R8Z49K5gRrgUTXPM5e66lDihPa7MDmH+mt/XOJ8wMa8FoK7vA110Fc1Bf1nFLud/
	+Q02ZZVc1oZzHF4Xd+7VLcBYPvSZ1/ahcSN7b5xP5SdhZsmYcfSz31EG3x0dBm5TR22qRl/Sy
	ZXcmmJ3kjSisoXKYiaT6qG5KzH92HQCvLmPaheLwka6oIVLHAZeahyYQjBxfyi/ICBF6kww07
	XZXF+bzoCtuH7Fp2mvQUnA6s9V58Qeh9pCKuOLxYuXL0sruiuj110i+BqB+aiQIHYk7CLJYb9
	JD0zcctL9qNG1XriUnzBjq7idmvqmo+C4y6b3R7j0BuRvnwwkJjw0q6O0SPjtoT/LQH5WjgAR
	hkh5B57WS9+vAaxfqR4INdMaCT0g6sJ4su3YxZbvQvPxNFXyxw/V4czeSsiMjVF0nx9kYk/0G
	fDHIhWCNDCDKg9v1o0enXoNY5RieVijr/mLVxPOB3E7nZQU34wN/vvH1CRRHhQz7tWnyQtX54
	EnYChXVBOscuosdGodXCh9Ve/yI3z+fqTVfc9he5fA==
X-Spam-Status:	No, score=-97.4 required=5.0 tests=BAYES_00,
	GOOD_FROM_CORINNA_CYGWIN, KAM_DMARC_STATUS, RCVD_IN_DNSWL_NONE,
	RCVD_IN_MSPIKE_H2, SPF_FAIL, SPF_HELO_NONE,
	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
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>
From:	Corinna Vinschen via Cygwin <cygwin AT cygwin DOT com>
Reply-To:	cygwin AT cygwin DOT com
Cc:	Corinna Vinschen <corinna-cygwin AT cygwin DOT com>, cygwin AT cygwin DOT com
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>

Hi Kai,

Apart from what Takashi already wrote, there's another bug in this code:

On Feb 16 12:04, Yeo Kai Wei via Cygwin wrote:
> #define ByteSize 512
> #define BackingFile "/shMemEx"
> #define AccessPerms 0644
> #define SemaphoreName "mysemaphore"
                        ^^^^^^^^^^^^

What Takashi wrote.  The reason that you don't notice that sem_open
actuially failed is...

> 	//Create the semaphore
> 	sem_t* semptr = sem_open(	SemaphoreName,//name 
> 					O_CREAT, //create semaphore
> 					AccessPerms, //protection permissions
> 					0);	//Initial value
> 
> 	//ERROR
> 	if(semptr == (void*) -1)
                     ^^^^^^^^^^
                     This.

Why do you test for -1?  If you read the POSIX man page for sem_open,
you'll see this:

  Upon successful completion, the sem_open() function shall return the
  address of the semaphore. Otherwise, it shall return a value of
  SEM_FAILED [...]
  ^^^^^^^^^^

SEM_FAILED is not necessarily -1.  On Cygwin it's defined as

  #define SEM_FAILED ((sem_t *) 0)

in /usr/include/semaphore.h.

So your code just seems to fail in sem_post, but actually that's
because sem_open failed and your code checks for the wrong return
value.


HTH,
Corinna

-- 
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

- Raw text -