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 sets 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 is any integer within the inclusive priority range for the scheduling policy specified by policy. If the value of pid is negative, the behaviour of the sched_setscheduler() function is unspecified.
The possible values for the policy parameter are defined in the header file <sched.h>.
If a process specified by pid exists and if the calling process has permission, the scheduling policy and scheduling parameters will be set for the process whose process ID is equal to pid.
If pid is zero, the scheduling policy and scheduling parameters will be set for the calling process.
The conditions under which one process has the appropriate privilege to change the scheduling parameters of another process are implementation-dependent.
Implementations may require that the requesting process have permission to set its own scheduling parameters or those of another process. Additionally, implementation-dependent restrictions may apply as to the appropriate privileges required to set a process's own scheduling policy, or another process's scheduling policy, to a particular value.
The sched_setscheduler() function is 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 have no effect on their scheduling.
- For threads with process scheduling contention scope, the threads' scheduling policy and associated parameters will 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.
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 will not be affected by these functions.
The underlying kernel scheduled entities for the process contention scope threads will have their scheduling policy and associated scheduling parameters changed to the values specified in policy and param, respectively. Kernel scheduled entities for use by process contention scope threads that are created after this call completes inherit their scheduling policy and associated scheduling parameters from the process.
This function is not atomic with respect to other threads in the process. Threads are allowed to 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.
Upon successful completion, the function returns the former scheduling policy of the specified process. If the sched_setscheduler() function fails to complete successfully, the policy and scheduling paramenters remain unchanged, and the function returns a value of -1 and sets errno to indicate the error.
The sched_setscheduler() function will 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 function sched_setscheduler() is not supported by this implementation.
- 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.
sched_getparam(), sched_getscheduler(), sched_setparam(), <sched.h>.
Derived from the POSIX Realtime Extension (1003.1b-1993/1003.1i-1995)