Scheduling policies

To meet the needs of various applications, BlackBerry PlayBook OS provides these scheduling algorithms:

  • FIFO scheduling
  • round-robin scheduling
  • sporadic scheduling

Each thread in the system may run using any method. The methods are effective on a per-thread basis, not on a global basis for all threads and processes on a node.

Remember that the FIFO and round-robin scheduling policies apply only when two or more threads that share the same priority are READY (i.e. the threads are directly competing with each other). The sporadic method, however, employs a budget for a thread's execution. In all cases, if a higher-priority thread becomes READY, it immediately preempts all lower-priority threads.

In the following diagram, three threads of equal priority are READY. If Thread A blocks, Thread B will run.

Figure showing scheduling of equal-priority threads where thread A blocks and thread B runs.

Although a thread inherits its scheduling policy from its parent process, the thread can request to change the algorithm applied by the kernel.