Change the priority and scheduling policy of a process
Synopsis:
#include <sched.h>
int sched_setscheduler(
pid_t pid,
int policy,
const struct sched_param *param );
Arguments:
- pid
- The ID of the process whose priority and scheduling policy you want to
set, or zero if you want to set them for the current process.
- policy
- The scheduling policy, which must be one of:
- SCHED_FIFO — a fixed-priority scheduler in which
the highest priority ready thread runs until it blocks or is preempted
by a higher priority thread.
- SCHED_RR — similar to SCHED_FIFO,
except that threads at the same priority level timeslice (round robin)
every 4 × the clock period (see
ClockPeriod()).
- SCHED_OTHER — currently the same as
SCHED_RR.
- SCHED_SPORADIC — sporadic scheduling.
For more information, see
Thread scheduling
in the QNX Neutrino Microkernel chapter of the
System Architecture guide.
- param
- A pointer to a
sched_param
structure whose
sched_priority member holds the priority that you want to
assign to the process.
Library:
libc
Use the -l c option to
qcc
to link against this library.
This library is usually included automatically.
Description:
The sched_setscheduler() function changes the priority of
process pid to that of the sched_priority member in
the sched_param structure passed as param, and the
scheduling policy is set to policy.
If pid is zero, the policy and priority of the calling process are set.
Note:
- In QNX Neutrino, scheduling is associated with threads, not processes, so
sched_setscheduler() sets
the scheduling policy for thread 1 in the process pid,
or for the calling thread if pid is 0.
- In order to set the scheduling policy and priority for a process whose user ID is different from
the calling process's real or effective user ID, your process must have the
PROCMGR_AID_SCHEDULE ability enabled.
In order to change its priority to a value above the maximum permitted for unprivileged processes,
your process must have the PROCMGR_AID_PRIORITY ability enabled.
For more information, see
procmgr_ability().
The sched_priority member in param must lie between
the minimum and maximum values returned by
sched_get_priority_max() and
sched_get_priority_min().
By default, the process priority and scheduling policy are inherited from
or explicitly set by the parent process.
Once running, the child process may change its priority by
using this function.
Returns:
The previous scheduling policy, or -1 if an error occurs
(errno is set).
Errors:
- EFAULT
- A fault occurred trying to access the buffers provided.
- EINVAL
- The priority or scheduling policy isn't a valid value.
- EPERM
- The calling process doesn't have the required permission; see
procmgr_ability().
- ESRCH
- The process pid doesn't exist.
Classification:
POSIX 1003.1 PS
Safety: |
|
Cancellation point |
No |
Interrupt handler |
No |
Signal handler |
Yes |
Thread |
Yes |