.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved 
.TH "SCHED_SETSCHEDULER" 3P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\" sched_setscheduler 
.SH PROLOG
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
.SH NAME
sched_setscheduler \- set scheduling policy and parameters (\fBREALTIME\fP)
.SH SYNOPSIS
.LP
\fB#include <sched.h>
.br
.sp
int sched_setscheduler(pid_t\fP \fIpid\fP\fB, int\fP \fIpolicy\fP\fB,
.br
\ \ \ \ \ \  const struct sched_param *\fP\fIparam\fP\fB); \fP
\fB
.br
\fP
.SH DESCRIPTION
.LP
The \fIsched_setscheduler\fP() function shall set the scheduling policy
and scheduling parameters of the process specified by
\fIpid\fP to \fIpolicy\fP and the parameters specified in the \fBsched_param\fP
structure pointed to by \fIparam\fP,
respectively. The value of the \fIsched_priority\fP member in the
\fBsched_param\fP structure shall be any integer within the
inclusive priority range for the scheduling policy specified by \fIpolicy\fP.
If the value of \fIpid\fP is negative, the behavior
of the \fIsched_setscheduler\fP() function is unspecified.
.LP
The possible values for the \fIpolicy\fP parameter are defined in
the \fI<sched.h>\fP header.
.LP
If a process specified by \fIpid\fP exists, and if the calling process
has permission, the scheduling policy and scheduling
parameters shall be set for the process whose process ID is equal
to \fIpid\fP.
.LP
If \fIpid\fP is zero, the scheduling policy and scheduling parameters
shall be set for the calling process.
.LP
The conditions under which one process has the appropriate privilege
to change the scheduling parameters of another process are
implementation-defined.
.LP
Implementations may require that the requesting process have permission
to set its own scheduling parameters or those of another
process. Additionally, implementation-defined restrictions may apply
as to the appropriate privileges required to set a process'
own scheduling policy, or another process' scheduling policy, to a
particular value.
.LP
The \fIsched_setscheduler\fP() function shall be considered successful
if it succeeds in setting the scheduling policy and
scheduling parameters of the process specified by \fIpid\fP to the
values specified by \fIpolicy\fP and the structure pointed to
by \fIparam\fP, respectively.
.LP
If
the scheduling policy specified by \fIpolicy\fP is SCHED_SPORADIC,
the value specified by the \fIsched_ss_low_priority\fP member
of the \fIparam\fP argument shall be any integer within the inclusive
priority range for the sporadic server policy. The
\fIsched_ss_repl_period\fP and \fIsched_ss_init_budget\fP members
of the \fIparam\fP argument shall represent the time
parameters used by the sporadic server scheduling policy for the target
process. The \fIsched_ss_max_repl\fP member of the
\fIparam\fP argument shall represent the maximum number of replenishments
that are allowed to be pending simultaneously for the
process scheduled under this scheduling policy.
.LP
The specified \fIsched_ss_repl_period\fP shall be greater than or
equal to the specified \fIsched_ss_init_budget\fP for the
function to succeed; if it is not, then the function shall fail.
.LP
The value of \fIsched_ss_max_repl\fP shall be within the inclusive
range [1, {SS_REPL_MAX}] for the function to succeed; if
not, the function shall fail.
.LP
If the scheduling policy specified by \fIpolicy\fP is either SCHED_FIFO
or SCHED_RR, the \fIsched_ss_low_priority\fP,
\fIsched_ss_repl_period\fP, and \fIsched_ss_init_budget\fP members
of the \fIparam\fP argument shall have no effect on the
scheduling behavior. 
.LP
The effect of this function on individual threads is dependent on
the scheduling contention scope of the threads:
.IP " *" 3
For threads with system scheduling contention scope, these functions
shall have no effect on their scheduling.
.LP
.IP " *" 3
For threads with process scheduling contention scope, the threads'
scheduling policy and associated parameters shall not be
affected. However, the scheduling of these threads with respect to
threads in other processes may be dependent on the scheduling
parameters of their process, which are governed using these functions.
.LP
.LP
If an implementation supports a two-level scheduling model in which
library threads are multiplexed on top of several
kernel-scheduled entities, then the underlying kernel-scheduled entities
for the system contention scope threads shall not be
affected by these functions.
.LP
The underlying kernel-scheduled entities for the process contention
scope threads shall have their scheduling policy and
associated scheduling parameters changed to the values specified in
\fIpolicy\fP and \fIparam\fP, respectively. Kernel-scheduled
entities for use by process contention scope threads that are created
after this call completes shall inherit their scheduling
policy and associated scheduling parameters from the process.
.LP
This function is not atomic with respect to other threads in the process.
Threads may continue to execute while this function
call is in the process of changing the scheduling policy and associated
scheduling parameters for the underlying kernel-scheduled
entities used by the process contention scope threads.
.SH RETURN VALUE
.LP
Upon successful completion, the function shall return the former scheduling
policy of the specified process. If the
\fIsched_setscheduler\fP() function fails to complete successfully,
the policy and scheduling parameters shall remain unchanged,
and the function shall return a value of -1 and set \fIerrno\fP to
indicate the error.
.SH ERRORS
.LP
The \fIsched_setscheduler\fP() function shall fail if:
.TP 7
.B EINVAL
The value of the \fIpolicy\fP parameter is invalid, or one or more
of the parameters contained in \fIparam\fP is outside the
valid range for the specified scheduling policy.
.TP 7
.B EPERM
The requesting process does not have permission to set either or both
of the scheduling parameters or the scheduling policy of
the specified process.
.TP 7
.B ESRCH
No process can be found corresponding to that specified by \fIpid\fP.
.sp
.LP
\fIThe following sections are informative.\fP
.SH EXAMPLES
.LP
None.
.SH APPLICATION USAGE
.LP
None.
.SH RATIONALE
.LP
None.
.SH FUTURE DIRECTIONS
.LP
None.
.SH SEE ALSO
.LP
\fIsched_getparam\fP(), \fIsched_getscheduler\fP(),
\fIsched_setparam\fP(), the Base Definitions volume of IEEE\ Std\ 1003.1-2001,
\fI<sched.h>\fP
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group. In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .