From mboxrd@z Thu Jan  1 00:00:00 1970
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Date: Wed, 21 Jun 2006 11:46:08 +0200
From: Jan Kiszka <jan.kiszka@domain.hid>
MIME-Version: 1.0
Subject: Re: [Xenomai-help] mutex locking
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To: =?ISO-8859-15?Q?Tobias_B=E4r?= <Tobias.Baer@domain.hid>
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Tobias B=E4r wrote:
> Hi all,
>=20
> my question is about the right way to lock and inquire a mutex. At time=
, my code looks like this:
>=20
>=20
> rt_mutex_inquire(&mutex,TM_NONBLOCK);
>=20
> if(info.lockcnt =3D=3D 0)=20
> {
>       rt_mutex_lock(&write_mutex,TM_NONBLOCK);
>=20
>       // do sth.
>=20
>       rt_mutex_unlock(&mutex);
> }
>=20
>=20
> What happens if anyone locks the mutex between my "rt_mutex_inquire(...=
)" and my "if(info.lockcnt =3D=3D 0)" ?
>=20
> Is this the standard way to lock and inquire a mutex?
>=20

Try this, it's safe from such races:

/* returns -EWOULDBLOCK if the mutex is locked */
if (rt_mutex_lock(&write_mutex,TM_NONBLOCK) =3D=3D 0)
{
      // do sth.

      rt_mutex_unlock(&mutex);
}

Jan


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