Ubuntu manuals

Provided by: freebsd-manpages_6.2-1_all

NAME

      chooseproc, procrunnable, remrunqueue, setrunqueue - manage the queue of
      runnable processes
 

SYNOPSIS

      #include <sys/param.h>
      #include <sys/proc.h>
 
      extern struct rq itqueues[];
      extern struct rq rtqueues[];
      extern struct rq queues[];
      extern struct rq idqueues[];
 
      struct thread *
      choosethread(void);
 
      int
      procrunnable(void);
 
      void
      remrunqueue(struct thread *td);
 
      void
      setrunqueue(struct thread *td);
 

DESCRIPTION

      The run queue consists of four priority queues: itqueues for interrupt
      threads, rtqueues for realtime priority processes, queues for time shar‐
      ing processes, and idqueues for idle priority processes.  Each priority
      queue consists of an array of NQS queue header structures.  Each queue
      header identifies a list of runnable processes of equal priority.  Each
      queue also has a single word that contains a bit mask identifying non-
      empty queues to assist in selecting a process quickly.  These are named
      itqueuebits, rtqueuebits, queuebits, and idqueuebits.  The run queues are
      protected by the sched_lock mutex.
 
      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 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 td from its run queue.  If td is not on a
      run queue, then the kernel will panic(9).  This function must be called
      with the sched_lock mutex held.
      cpu_switch(9), scheduler(9), sleepqueue(9)