Thread Scheduling

The POSIX standard specifies three scheduling policies: first-in-first-out (SCHED_FIFO), round-robin (SCHED_RR), and custom (SCHED_OTHER). SCHED_FIFO is a queue-based scheduler with different queues for each priority level. SCHED_RR is like FIFO except that each thread has an execution time quota.

Both SCHED_FIFO and SCHED_RR are POSIX Realtime extensions. Threads executing with these policies are in the Solaris Real-Time (RT) scheduling class, normally requiring special privilege. SCHED_OTHER is the default scheduling policy. Threads executing with the SCHED_OTHER policy are in the traditional Solaris Time-Sharing (TS) scheduling class.

Solaris provides other scheduling classes, namely the Interactive timesharing (IA) class, the Fair-Share (FSS) class, and the Fixed-Priority (FX) class. Such specialized classes are not discussed here. See the Solaris priocntl(2) manual page for more information.

See LWPs and Scheduling Classes for information about the SCHED_OTHER policy.

Two scheduling scopes are available: process scope (PTHREAD_SCOPE_PROCESS) and system scope (PTHREAD_SCOPE_SYSTEM). Threads with differing scope states can coexist on the same system and even in the same process. Process scope causes such threads to contend for resources only with other such threads in the same process. System scope causes such threads to contend with all other threads in the system. In practice, beginning with the Solaris 9 release, the system makes no distinction between these two scopes.