POSIX Threads for Windows – REFERENCE - Pthreads-w32

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sched_setscheduler - set scheduling policy and parameters (REALTIME)


#include <sched.h>

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


The sched_setscheduler function shall set the scheduling policy and scheduling parameters of the process specified by pid to policy and the parameters specified in the sched_param structure pointed to by param, respectively. The value of the sched_priority member in the sched_param structure shall be any integer within the inclusive priority range for the scheduling policy specified by policy. If the value of pid is negative, the behavior of the sched_setscheduler function is unspecified.

The possible values for the policy parameter are defined in the <sched.h> header.

Pthreads-w32 only supports the SCHED_OTHER policy. Any other value for policy will return failure with errno set to ENOSYS. However, checks on pid and permissions are performed first so that the other useful side effects of this routine are retained.

If a process specified by pid 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 pid.

If pid is zero, the scheduling policy and scheduling parameters shall be set for the calling process.

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.

The sched_setscheduler function shall be considered successful if it succeeds in setting the scheduling policy and scheduling parameters of the process specified by pid to the values specified by policy and the structure pointed to by param, respectively.

The effect of this function on individual threads is dependent on the scheduling contention scope of the threads:

For threads with system scheduling contention scope, these functions shall have no effect on their scheduling.
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.

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.

Return Value

Upon successful completion, the function shall return the former scheduling policy of the specified process. If the sched_setscheduler function fails to complete successfully, the policy and scheduling parameters shall remain unchanged, and the function shall return a value of -1 and set errno to indicate the error.


The sched_setscheduler function shall fail if:

The value of the policy parameter is invalid, or one or more of the parameters contained in param is outside the valid range for the specified scheduling policy.
The requesting process does not have permission to set either or both of the scheduling parameters or the scheduling policy of the specified process.
No process can be found corresponding to that specified by pid.

The following sections are informative.



Application Usage




Future Directions


See Also

sched_getscheduler(3) , the Base Definitions volume of IEEE Std 1003.1-2001, <sched.h>


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 .

Modified by Ross Johnson for use with Pthreads-w32.

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