NAME

sched.h - execution scheduling (REALTIME)

SYNOPSIS

^[PS] #include <sched.h>

DESCRIPTION

The <sched.h> header shall define the sched_param structure, which contains the scheduling parameters required for implementation of each supported scheduling policy. This structure shall contain at least the following member:

int       sched_priority        Process execution scheduling priority. 

^[SS|TSP] In addition, if _POSIX_SPORADIC_SERVER or _POSIX_THREAD_SPORADIC_SERVER is defined, the sched_param structure defined in <sched.h> shall contain the following members in addition to those specified above:

int             sched_ss_low_priority Low scheduling priority for 
                                      sporadic server. 
struct timespec sched_ss_repl_period  Replenishment period for 
                                      sporadic server. 
struct timespec sched_ss_init_budget  Initial budget for sporadic server. 
int             sched_ss_max_repl     Maximum pending replenishments for 
                                      sporadic server. 

Each process is controlled by an associated scheduling policy and priority. Associated with each policy is a priority range. Each policy definition specifies the minimum priority range for that policy. The priority ranges for each policy may overlap the priority ranges of other policies.

Four scheduling policies are defined; others may be defined by the implementation. The four standard policies are indicated by the values of the following symbolic constants:

SCHED_FIFO

First in-first out (FIFO) scheduling policy.

SCHED_RR

Round robin scheduling policy.

SCHED_SPORADIC

^[SS|TSP] Sporadic server scheduling policy.

SCHED_OTHER

Another scheduling policy.

The values of these constants are distinct.

The following shall be declared as functions and may also be defined as macros. Function prototypes shall be provided.

[TPS]
int    sched_get_priority_max(int);
int    sched_get_priority_min(int);

int    sched_getparam(pid_t, struct sched_param *);
int    sched_getscheduler(pid_t);
[TPS]
int    sched_rr_get_interval(pid_t, struct timespec *);

int    sched_setparam(pid_t, const struct sched_param *);
int    sched_setscheduler(pid_t, int, const struct sched_param *);
[THR]
int    sched_yield(void);

Inclusion of the <sched.h> header may make visible all symbols from the <time.h> header.

APPLICATION USAGE

None.

RATIONALE

None.

FUTURE DIRECTIONS

None.

SEE ALSO

<time.h>

CHANGE HISTORY

First released in Issue 5. Included for alignment with the POSIX Realtime Extension.

Issue 6

The <sched.h> header is marked as part of the Process Scheduling option.

Sporadic server members are added to the sched_param structure, and the SCHED_SPORADIC scheduling policy is added for alignment with IEEE Std 1003.1d-1999.

IEEE PASC Interpretation 1003.1 #108 is applied, correcting the sched_param structure whose members sched_ss_repl_period and sched_ss_init_budget should be type struct timespec and not timespec.

Symbols from <time.h> may be made visible when <sched.h> is included.

IEEE Std 1003.1-2001/Cor 1-2002, items XSH/TC1/D6/52 and XSH/TC1/D6/53 are applied, aligning the function prototype shading and margin codes with the System Interfaces volume of IEEE Std 1003.1-2001.