Re: For review: pthread_attr_setinheritsched.3

[Loic Domaigne <tech-Z4JMKDdsf89Wk0Htik3J/w@public.gmane.org>]

Moin, Moin,

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

Cheers,
Loïc.
--

> .\" Copyright (c) 2008 Linux Foundation, written by Michael Kerrisk
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> .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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