sched_setparam - set scheduling parameters (REALTIME)
#include <sched.h> int sched_setparam(pid_t pid, const struct sched_param *param);
The sched_setparam() function sets the scheduling parameters of the process specified by pid to the values specified by the sched_param structure pointed to by param. The value of the sched_priority member in the sched_param structure is any integer within the inclusive priority range for the current scheduling policy of the process specified by pid. Higher numerical values for the priority represent higher priorities. If the value of pid is negative, the behaviour of the sched_setparam() function is unspecified.
If a process specified by pid exists and if the calling process has permission, the scheduling parameters will be set for the process whose process ID is equal to pid.
If pid is zero, the scheduling parameters will be set for the calling process.
The conditions under which one process has permission to change the scheduling parameters of another process are implementation-dependent.
Implementations may require the requesting process to have the appropriate privilege to set its own scheduling parameters or those of another process.
The target process, whether it is running or not running, resumes execution after all other runnable processes of equal or greater priority have been scheduled to run.
If the priority of the process specified by the pid 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 pid argument preempts a lowest priority running process. Similarly, if the process calling sched_setparam() 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 also preempts 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.
If the current scheduling policy for the process specified by pid is not SCHED_FIFO or SCHED_RR, including SCHED_OTHER, the result is implementation-dependent.
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 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 parameters changed to the value specified in param. 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 for the underlying kernel scheduled entities used by the process contention scope threads.
If successful, the sched_setparam() function returns zero.
If the call to sched_setparam() is unsuccessful, the priority remains unchanged, and the function returns a value of -1 and sets errno to indicate the error.
The sched_setparam() function will fail if:
- One or more of the requested scheduling parameters is outside the range defined for the scheduling policy of the specified pid.
- The function sched_setparam() is not supported by this implementation.
- 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 sched_setparam().
- No process can be found corresponding to that specified by pid.
sched_getparam(), sched_getscheduler(), sched_setscheduler(), <sched.h>.
Derived from the POSIX Realtime Extension (1003.1b-1993/1003.1i-1995)