.\"   $Id: Csched.man 3515 2010-04-05 07:51:26Z baud $
.\"
.\"   Man page for the LCG's Scheduling Interface (Csched)
.\"
.TH CSCHED "3" "$Date: 2010-04-05 09:51:26 +0200 (Mon, 05 Apr 2010) $" "LCG" "Common Library Functions"
.SH NAME
\fBCsched\fP \- \fBLCG\fP \fBScheduling\fP inferface
.SH SYNOPSIS
.B #include <Csched_api.h>
.P
.BI "int Csched_getschedparam(int " cid ", int *" policy ", Csched_param_t *" param ");"
.P
.BI "int Csched_setschedparam(int " cid ", int " policy ", Csched_param_t *" param ");"
.P
.BI "int Csched_get_priority_min(int " policy ");"
.P
.BI "int Csched_get_priority_mid(int " policy ");"
.P
.BI "int Csched_get_priority_max(int " policy ");"

.SH ERRORS
Beyond the errno value, \fBCsched\fP is setting the serrno value to generic values that are described in \fBCthread\fP(1).

.SH DESCRIPTION

\fBCsched\fP is a common API interface for scheduling of multithreaded programs.
.P
\fBCsched_getschedparam\fP retrieves the current scheduling policy and priority of the thread referenced with Cthread's id
.I cid.
The
.I policy
can be
.I CSCHED_OTHER, CSCHED_FIFO, CSCHED_RR, CSCHED_FG_NP
or
.I CSCHED_BG_NP.
The
.I param
structure contains a member, named
.I sched_priority
, where will be stored the current priority of the thread you ask for. Please read the
.B NOTES
section.
.P
Return value is 0 on success, or -1 on error.
.P
\fBCsched_setschedparam\fP sets the scheduling policy and priority of the thread referenced with Cthread's id
.I cid.
The
.I policy
can be
.I CSCHED_OTHER, CSCHED_FIFO, CSCHED_RR, CSCHED_FG_NP
or
.I CSCHED_BG_NP.
You are neverthless
.B warned
that the
.B recommended
scheduling is
.I CSCHED_OTHER.
Trying to use another scheduling is an opendoor to processor deadlock if you do not code with extreme care. Furthermore, except
.I CSCHED_OTHER
, it is
.B not
guaranteed that the other possible values (
.I CSCHED_CSCHED_FIFO, CSCHED_RR, CSCHED_FG_NP
or
.I CSCHED_BG_NP
) are supported or implemented on your platform.
The
.I param
structure contains a member, named
.I sched_priority
, where is given the priority of the thread you want the attributes to be modified. Its value can vary from
.BI "Csched_get_priority_min(" policy ")
to
.BI "Csched_get_priority_max(" policy ").
Please read the
.B NOTES
section.
.P
Return value is 0 on success, or -1 on error.
.P
\fBCsched_get_priority_min\fP, \fBCsched_get_priority_mid\fP and \fBCsched_get_priority_max\fB are returning the minimum, medium and maximum allowed priorities, respectively, vs. the given
.I policy.
The output is the one that you use in the
.I sched_priority
member of the Csched_param_t structure. Please read the
.B NOTES
section.
.P
Return value is != -1 on success, or -1 on error.
.SH NOTES
About scheduling, the Csched interface defines
.I CSCHED_OTHER, CSCHED_FIFO, CSCHED_RR, CSCHED_FG_NP
and
.I CSCHED_BG_NP
for portability issue. This does
.B not
mean that all those schedulings are supported on the platform you are running on. In particular, only
.I CSCHED_OTHER
is officially supported everywhere. The other scheduling policies are totally system dependent and do not conform to any standardisation. Please be aware, also, that using a scheduling other than
.I CSCHED_OTHER
is an opendoor to processor deadlock...
.P
Finally, on some OSes, the scheduling interfaces are not necessarly in the thread library, nor in the C library. In particular, on Digital you may find them in librt, and on Solaris in libposix4.

.SH SEE ALSO
\fBCthread\fP

.SH AUTHOR
\fBLCG Grid Deployment\fP Team