SchedSet(), SchedSet_r()

Set the scheduling policy and parameters for a thread


#include <sys/neutrino.h>

int SchedSet( 
       pid_t pid,
       int tid,
       int policy,
       const struct sched_param *param );

int SchedSet_r(
       pid_t pid,
       int tid,
       int policy,
       const struct sched_param *param );


0 or a process ID; see below.
0 or a thread ID; see below.
The scheduling policy; 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 — the same as SCHED_FIFO, except 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.
  • SCHED_NOCHANGE — this isn't actually a policy, but a special value that tells the kernel to update the parameters specified in param, without changing the policy.
  • SCHED_ADJTOHEAD — if the thread specified by pid and tid is READY, put it at the head of the READY queue.
  • SCHED_ADJTOTAIL — if the thread specified by pid and tid is READY, put it at the tail of the READY queue.
    Note: If you specify SCHED_ADJTOHEAD or SCHED_ADJTOTAIL, the param argument is ignored.

For more information, see "Thread scheduling" in the QNX Neutrino Microkernel chapter of the System Architecture guide.

A pointer to a sched_param structure that holds the new scheduling parameters.



Use the -l c option to qcc to link against this library. This library is usually included automatically.


The SchedSet() and SchedSet_r() kernel calls set both the scheduling policy and the associated parameters for the thread specified by tid in the process specified by pid. If pid is zero, the current process is used to look up a nonzero tid. If tid is zero, then the calling thread is used and pid is ignored.

These functions are identical except in the way they indicate errors. See the Returns section for details.

  • Instead of using these kernel calls directly, consider calling pthread_setschedparam(), pthread_setschedprio(), sched_setparam(), or sched_setscheduler().
  • In order to set the scheduling policy and parameters for a thread whose real or saved 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 set the priority above the maximum allowed for unprivileged processes, your process must have the PROCMGR_AID_PRIORITY ability enabled. For more information, see procmgr_ability().

Blocking states

These calls don't block.


The only difference between these functions is the way they indicate errors:

If an error occurs, -1 is returned and errno is set. Any other value returned indicates success.
EOK is returned on success. This function does NOT set errno. If an error occurs, any value in the Errors section may be returned.


A fault occurred when the kernel tried to access the buffers you provided.
The given scheduling policy is invalid.
The calling process doesn't have the required permission; see procmgr_ability().
The process indicated by pid or thread indicated by tid doesn't exist.


QNX Neutrino

Cancellation point No
Interrupt handler No
Signal handler Yes
Thread Yes