For review: pthread_attr_setinheritsched.3

For review: pthread_attr_setinheritsched.3

[Michael Kerrisk]

.\" Copyright (c) 2008 Linux Foundation, written by Michael Kerrisk
.\"     <mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
.\"
.\" Permission is granted to make and distribute verbatim copies of this
.\" manual provided the copyright notice and this permission notice are
.\" preserved on all copies.
.\"
.\" Permission is granted to copy and distribute modified versions of this
.\" manual under the conditions for verbatim copying, provided that the
.\" entire resulting derived work is distributed under the terms of a
.\" permission notice identical to this one.
.\"
.\" Since the Linux kernel and libraries are constantly changing, this
.\" manual page may be incorrect or out-of-date.  The author(s) assume no
.\" responsibility for errors or omissions, or for damages resulting from
.\" the use of the information contained herein.  The author(s) may not
.\" have taken the same level of care in the production of this manual,
.\" which is licensed free of charge, as they might when working
.\" professionally.
.\"
.\" Formatted or processed versions of this manual, if unaccompanied by
.\" the source, must acknowledge the copyright and authors of this work.
.\"
.TH PTHREAD_ATTR_SETINHERITSCHED 3 2008-11-06 "Linux" "Linux
Programmer's Manual"
.SH NAME
pthread_attr_setinheritsched, pthread_attr_getinheritsched \- set/get
inherit scheduler attribute in thread attributes object
.SH SYNOPSIS
.nf
.B #include <pthread.h>

.BI "int pthread_attr_setinheritsched(pthread_attr_t *" attr ,
.BI "                                 int " inheritsched );
.BI "int pthread_attr_getinheritsched(pthread_attr_t *" attr ,
.BI "                                 int *" inheritsched );
.sp
Compile and link with \fI\-pthread\fP.
.SH DESCRIPTION
The
.BR pthread_attr_setinheritsched ()
function sets the inherit scheduler attribute of the
thread attributes object referred to by
.IR thread
to the value specified in
.IR inheritsched .
The inherit scheduler attribute determines whether a thread created using
the thread attributes object
.I attr
will inherit its scheduling attributes from the calling thread
or whether it will take them from
.IR attr .

The following values may be specified in
.IR inheritsched :
.TP
.B PTHREAD_INHERIT_SCHED
Threads that are created using
.I attr
inherit scheduling attributes from the creating thread;
the scheduling attributes in
.I attr
are ignored.
.TP
.B PTHREAD_EXPLICIT_SCHED
Threads that are created using
.I attr
take their scheduling attributes from the values specified
by the attributes object.
.\" FIXME what are the defaults for scheduler settings?
.PP
The default setting of the inherit scheduler attribute in
a newly initialized thread attributes object is
.BR PTHREAD_INHERIT_SCHED .

The
.BR pthread_attr_getinheritsched ()
returns the inherit scheduler attribute of the thread attributes object
.IR attr
in the buffer pointed to by
.IR inheritsched .
.SH RETURN VALUE
On success, these functions return 0;
on error, they return a non-zero error number.
.SH ERRORS
.BR pthread_attr_setinheritsched ()
can fail with the following error:
.TP
.B EINVAL
Invalid value in
.IR inheritsched .
.PP
POSIX.1-2001 also documents an optional
.B ENOTSUP
error ("attempt was made to set the attribute to an unsupported value") for
.BR pthread_attr_setinheritsched ().
.\" .SH VERSIONS
.\" Available since glibc 2.0.
.SH CONFORMING TO
POSIX.1-2001.
.SH EXAMPLE
See
.BR pthread_setschedparam (3).
.SH BUGS
As at glibc 2.8, if a thread attributes object is initialized using
.BR pthread_attr_init (3),
then the scheduling policy of the attributes object is set to
.BR SCHED_OTHER
and the scheduling priority is set to 0.
However, if the inherit scheduler attribute is then set to
.BR PTHREAD_EXPLICIT_SCHED ,
then a thread created using the attribute object
wrongly inherits its scheduling attributes from the creating thread.
This bug does not occur if either the scheduling policy or
scheduling priority attribute is explicitly set
in the thread attributes object before calling
.BR pthread_create (3).
.\" FIXME . Track status of the following bug:
.\" http://sourceware.org/bugzilla/show_bug.cgi?id=7007
.SH SEE ALSO
.BR sched_setscheduler (2),
.BR pthread_attr_init (3),
.BR pthread_attr_setschedparam (3),
.BR pthread_attr_setschedpolicy (3),
.BR pthread_create (3),
.BR pthread_setschedparam (3),
.BR pthread_setschedprio (3),
.BR pthreads (7)


-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
git://git.kernel.org/pub/scm/docs/man-pages/man-pages.git
man-pages online: http://www.kernel.org/doc/man-pages/online_pages.html
Found a bug? http://www.kernel.org/doc/man-pages/reporting_bugs.html
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Re: For review: pthread_attr_setinheritsched.3

[Loic Domaigne]

Moin, Moin,

yet another review... Enough for today ;-)

Cheers,
Loïc.
--

> .\" Copyright (c) 2008 Linux Foundation, written by Michael Kerrisk
> .\"     <mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
> .\"
> .\" Permission is granted to make and distribute verbatim copies of this
> .\" manual provided the copyright notice and this permission notice are
> .\" preserved on all copies.
> .\"
> .\" Permission is granted to copy and distribute modified versions of this
> .\" manual under the conditions for verbatim copying, provided that the
> .\" entire resulting derived work is distributed under the terms of a
> .\" permission notice identical to this one.
> .\"
> .\" Since the Linux kernel and libraries are constantly changing, this
> .\" manual page may be incorrect or out-of-date.  The author(s) assume no
> .\" responsibility for errors or omissions, or for damages resulting from
> .\" the use of the information contained herein.  The author(s) may not
> .\" have taken the same level of care in the production of this manual,
> .\" which is licensed free of charge, as they might when working
> .\" professionally.
> .\"
> .\" Formatted or processed versions of this manual, if unaccompanied by
> .\" the source, must acknowledge the copyright and authors of this work.
> .\"
> .TH PTHREAD_ATTR_SETINHERITSCHED 3 2008-11-06 "Linux" "Linux
> Programmer's Manual"
> .SH NAME
> pthread_attr_setinheritsched, pthread_attr_getinheritsched \- set/get
> inherit scheduler attribute in thread attributes object
> .SH SYNOPSIS
> .nf
> .B #include <pthread.h>
> 
> .BI "int pthread_attr_setinheritsched(pthread_attr_t *" attr ,
> .BI "                                 int " inheritsched );
> .BI "int pthread_attr_getinheritsched(pthread_attr_t *" attr ,
> .BI "                                 int *" inheritsched );
> .sp
> Compile and link with \fI\-pthread\fP.
> .SH DESCRIPTION
> The
> .BR pthread_attr_setinheritsched ()
> function sets the inherit scheduler attribute of the
> thread attributes object referred to by
> .IR thread

should be "attr"

> to the value specified in
> .IR inheritsched .
> The inherit scheduler attribute determines whether a thread created using
> the thread attributes object
> .I attr
> will inherit its scheduling attributes from the calling thread
> or whether it will take them from
> .IR attr .
> 
> The following values may be specified in
> .IR inheritsched :
> .TP
> .B PTHREAD_INHERIT_SCHED
> Threads that are created using
> .I attr
> inherit scheduling attributes from the creating thread;
> the scheduling attributes in
> .I attr
> are ignored.
> .TP
> .B PTHREAD_EXPLICIT_SCHED
> Threads that are created using
> .I attr
> take their scheduling attributes from the values specified
> by the attributes object.
> .\" FIXME what are the defaults for scheduler settings?
> .PP
> The default setting of the inherit scheduler attribute in
> a newly initialized thread attributes object is
> .BR PTHREAD_INHERIT_SCHED .
> 
> The
> .BR pthread_attr_getinheritsched ()
> returns the inherit scheduler attribute of the thread attributes object
> .IR attr
> in the buffer pointed to by
> .IR inheritsched .
> .SH RETURN VALUE
> On success, these functions return 0;
> on error, they return a non-zero error number.
> .SH ERRORS
> .BR pthread_attr_setinheritsched ()
> can fail with the following error:
> .TP
> .B EINVAL
> Invalid value in
> .IR inheritsched .
> .PP
> POSIX.1-2001 also documents an optional
> .B ENOTSUP
> error ("attempt was made to set the attribute to an unsupported value") for
> .BR pthread_attr_setinheritsched ().
> .\" .SH VERSIONS
> .\" Available since glibc 2.0.
> .SH CONFORMING TO
> POSIX.1-2001.
> .SH EXAMPLE
> See
> .BR pthread_setschedparam (3).
> .SH BUGS
> As at glibc 2.8, if a thread attributes object is initialized using
> .BR pthread_attr_init (3),
> then the scheduling policy of the attributes object is set to
> .BR SCHED_OTHER
> and the scheduling priority is set to 0.
> However, if the inherit scheduler attribute is then set to
> .BR PTHREAD_EXPLICIT_SCHED ,
> then a thread created using the attribute object
> wrongly inherits its scheduling attributes from the creating thread.
> This bug does not occur if either the scheduling policy or
> scheduling priority attribute is explicitly set
> in the thread attributes object before calling
> .BR pthread_create (3).
> .\" FIXME . Track status of the following bug:
> .\" http://sourceware.org/bugzilla/show_bug.cgi?id=7007

You raised an interesting issue. I checked the code responsible for
pthread_create(). As a matter of fact, Glibc shall only take the 
explicit scheduling if either the policy or priority has been set. This 
makes somehow sense: if you want explicit scheduling, you should at 
least set one of the two parameters, shouldn't you?

I was wondering how other Pthreads implementation behave in this case. 
Did you discuss this topic on Austin?


> .SH SEE ALSO
> .BR sched_setscheduler (2),
> .BR pthread_attr_init (3),
> .BR pthread_attr_setschedparam (3),
> .BR pthread_attr_setschedpolicy (3),
> .BR pthread_create (3),
> .BR pthread_setschedparam (3),
> .BR pthread_setschedprio (3),
> .BR pthreads (7)
> 
> 

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Re: For review: pthread_attr_setinheritsched.3

[Michael Kerrisk]

Hi Loic,


> yet another review... Enough for today ;-)

And thanks once again!

[...]

>> .SH DESCRIPTION
>> The
>> .BR pthread_attr_setinheritsched ()
>> function sets the inherit scheduler attribute of the
>> thread attributes object referred to by
>> .IR thread
> 
> should be "attr"

Thanks; fixed.

[...]

>> .SH BUGS
>> As at glibc 2.8, if a thread attributes object is initialized using
>> .BR pthread_attr_init (3),
>> then the scheduling policy of the attributes object is set to
>> .BR SCHED_OTHER
>> and the scheduling priority is set to 0.
>> However, if the inherit scheduler attribute is then set to
>> .BR PTHREAD_EXPLICIT_SCHED ,
>> then a thread created using the attribute object
>> wrongly inherits its scheduling attributes from the creating thread.
>> This bug does not occur if either the scheduling policy or
>> scheduling priority attribute is explicitly set
>> in the thread attributes object before calling
>> .BR pthread_create (3).
>> .\" FIXME . Track status of the following bug:
>> .\" http://sourceware.org/bugzilla/show_bug.cgi?id=7007
> 
> You raised an interesting issue. I checked the code responsible for
> pthread_create(). As a matter of fact, Glibc shall only take the 
> explicit scheduling if either the policy or priority has been set.

Agreed, that is what I also determined from reading the code.

> This
> makes somehow sense: if you want explicit scheduling, you should at 
> least set one of the two parameters, shouldn't you?

Yes, except that there are defaults that can be inspected in the
attr object, and these defaults are not honored when a thread is
actually created.  That seems wrong to me.

> I was wondering how other Pthreads implementation behave in this case. 
> Did you discuss this topic on Austin?

I didn't raise this on Austin, but Solaris 8 does what I would expect.

Cheers,

Michael


-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
git://git.kernel.org/pub/scm/docs/man-pages/man-pages.git
man-pages online: http://www.kernel.org/doc/man-pages/online_pages.html
Found a bug? http://www.kernel.org/doc/man-pages/reporting_bugs.html

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