path: root/man3p/sched_setparam.3p

.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved 
.TH "SCHED_SETPARAM" P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\" sched_setparam 
.SH NAME
sched_setparam \- set scheduling parameters (\fBREALTIME\fP)
.SH SYNOPSIS
.LP
\fB#include <sched.h>
.br
.sp
int sched_setparam(pid_t\fP \fIpid\fP\fB, const struct sched_param
*\fP\fIparam\fP\fB); \fP
\fB
.br
\fP
.SH DESCRIPTION
.LP
The \fIsched_setparam\fP() function shall set the scheduling parameters
of the process specified by \fIpid\fP to the values
specified by the \fBsched_param\fP structure pointed to by \fIparam\fP.
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 current scheduling policy of the
process specified by \fIpid\fP. Higher numerical values for the priority
represent higher priorities. If the value of \fIpid\fP
is negative, the behavior of the \fIsched_setparam\fP() function is
unspecified.
.LP
If a process specified by \fIpid\fP exists, and if the calling process
has permission, the scheduling parameters shall be set
for the process whose process ID is equal to \fIpid\fP.
.LP
If \fIpid\fP is zero, the scheduling parameters shall be set for the
calling process.
.LP
The conditions under which one process has permission to change the
scheduling parameters of another process are
implementation-defined.
.LP
Implementations may require the requesting process to have the appropriate
privilege to set its own scheduling parameters or
those of another process.
.LP
The target process, whether it is running or not running, shall be
moved to the tail of the thread list for its priority.
.LP
If the priority of the process specified by the \fIpid\fP argument
is set higher than that of the lowest priority running
process and if the specified process is ready to run, the process
specified by the \fIpid\fP argument shall preempt a lowest
priority running process. Similarly, if the process calling \fIsched_setparam\fP()
sets its own priority lower than that of one or
more other non-empty process lists, then the process that is the head
of the highest priority list shall also preempt the calling
process. Thus, in either case, the originating process might not receive
notification of the completion of the requested priority
change until the higher priority process has executed.
.LP
If
the scheduling policy of the target process 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 to be 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 of the target process 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. If the scheduling policy of this process is not
SCHED_FIFO, SCHED_RR, or SCHED_SPORADIC, the effects of these
members are implementation-defined; this case includes the SCHED_OTHER
policy. 
.LP
If the current scheduling policy for the process specified by \fIpid\fP
is not SCHED_FIFO, SCHED_RR,   \ or
SCHED_SPORADIC,  \ the result is implementation-defined; this
case includes the SCHED_OTHER policy.
.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 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 parameters changed
to the value specified in \fIparam\fP. 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 for the underlying
kernel-scheduled entities used by the process
contention scope threads.
.SH RETURN VALUE
.LP
If successful, the \fIsched_setparam\fP() function shall return zero.
.LP
If the call to \fIsched_setparam\fP() is unsuccessful, the priority
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_setparam\fP() function shall fail if:
.TP 7
.B EINVAL
One or more of the requested scheduling parameters is outside the
range defined for the scheduling policy of the specified
\fIpid\fP.
.TP 7
.B EPERM
The requesting process does not have permission to set the scheduling
parameters for the specified process, or does not have
the appropriate privilege to invoke \fIsched_setparam\fP().
.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_setscheduler\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 .