Партнёры:
Хостинг:
chooseproc procrunnable remrunqueue setrunqueue - manage the queue of runnable processes
procrunnable ();
returns zero if there are no runnable processes other than the idle process.
If there is at least one runnable process other than the idle process, it
will return a non-zero value.
Note that the
sched_lock
mutex does
not
need to be held when this function is called.
There is a small race window where one CPU may place a process on the run queue
when there are currently no other runnable processes while another CPU is
calling this function.
In that case the second CPU will simply travel through the idle loop one
additional time before noticing that there is a runnable process.
This works because idle CPUs are not halted in SMP systems.
If idle CPUs are halted in SMP systems, then this race condition might have
more serious repercussions in the losing case, and
procrunnable ();
may have to require that the
sched_lock
mutex be acquired.
choosethread ();
returns the highest priority runnable thread.
If there are no runnable threads, then the idle thread is returned.
This function is called by
cpu_switch ();
and
cpu_throw ();
to determine which thread to switch to.
choosethread ();
must be called with the
sched_lock
mutex held.
setrunqueue ();
adds the thread
Fa td
to the tail of the appropriate queue in the proper priority queue.
The thread must be runnable, i.e.
p_stat
must be set to
SRUN
This function must be called with the
sched_lock
mutex held.
remrunqueue ();
removes thread
Fa td
from its run queue.
If
Fa td
is not on a run queue, then the kernel will
panic(9).
This function must be called with the
sched_lock
mutex held.
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