Thread Scheduling

Scheduling Scope

• Kernel threads PTHREAD_SCOPE_SYSTEM
• User Threads PTHREAD_SCOPE_PROCESS
• Most implementations will only support one.
• Only settable at thread creation.

int pthread_attr_getscope(pthread_attr_t * attr, int * scope);

int pthread_attr_setscope(pthread_attr_t * attr, int scope);

Policy and Priority

• Must support SCHED_RR, SCHED_FIFO, and SCHED_OTHER.
• Round Robin and FIFO have realtime semantics.
• The priority of OTHER threads is usually for fair schedulers
• Policy and Priority are settable at thread creation time or dynamically.

int pthread_attr_getschedpolicy(pthread_attr_t * attr, int * policy);

int pthread_attr_setschedpolicy(pthread_attr_t * attr, int policy);

int pthread_attr_getschedparam(pthread_attr_t * attr, struct sched_param * param);

int pthread_attr_setschedparam(pthread_attr_t * attr, struct sched_param * param);

int pthread_getschedparam(pthread_t, int * policy, struct sched_param * param);

int pthread_setschedparam(pthread_t, int * policy, struct sched_param * param);

Struct sched_param

• Part of the POSIX Realtime specification

struct sched_param {
	int sched_priority;
	...
};

int sched_get_priority_max(int);

int sched_get_priority_min(int);

Yield

int sched_yield(void);

• SCHED_FIFO and SCHED_RR only yields to a thread of the same priority.
• SCHED_OTHER may have more UNIX like behavior.

Scheduling Inheritance

int pthread_attr_getinheritsched(pthread_attr_t *, int * inherit);

int pthread_attr_setinheritsched(pthread_attr_t *, int inherit);

• PTHREAD_INHERIT_SCHED causes create to ignore attr attributes and inherit from the parent thread.
• PTHREAD_EXPLICIT_SCHED is the default.