FreeBSD/Linux Kernel Cross Reference
sys/man/thread_set_policy.man

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    .\" HISTORY
    .\" $Log:       thread_set_policy.man,v $
    .\" Revision 2.2  93/12/07  13:59:11  dbg
    .\"     Created.
    .\" 
    .\" 
    .TH thread_set_policy 2 9/22/93
    .CM 4
    .SH NAME
    .nf
    thread_set_policy  \-  set scheduling policy for a thread
    .SH SYNOPSIS
    .nf
    .ft B
    #include <mach.h>
    
    .nf
    .ft B
    kern_return_t thread_set_policy(
            thread_t        thread,
            processor_set_t pset,
            int             policy,
            policy_param_t  param,
            natural_t       param_count);
    
    
    .fi
    .ft P
    .SH ARGUMENTS
    .TP 15
    .B
    thread
    Thread to set policy for.
    .TP 15
    .B
    pset
    The control port for the processor set to which thread is assigned.
    .TP 15
    .B
    policy
    Policy to set.
    .TP 15
    .B
    param[param_count]
    Policy-specific parameters.
    
    .SH DESCRIPTION
    .B thread_set_policy
    changes the scheduling policy for 
    .B thread
    to 
    .B policy.
    
    .B param
    is policy-dependent scheduling information.  The base system supports
    three scheduling policies: 
    .B POLICY_FIXEDPRI,
    .B POLICY_TIMESHARE
    and 
    .B POLICY_BACKGROUND,
    defined in <mach/policy.h>; this file is included by mach.h.  Fixed-priority
    threads are chosen to run before any timesharing threads; in turn,
    timesharing threads are chosen before any background threads.  Within
    each policy, the policy parameters for each thread determines which
    thread is chosen to run.
    
    .B POLICY_BACKGROUND
    
    Background threads run only if no other threads in the system are runnable.
    They are scheduled in a round-robin fashion.
    .B param
    is not used.
    
   .B POLICY_TIMESHARE
   
   Timesharing threads have a base priority value ranging from 0 (highest)
   to 31 (lowest).  The actual priority used for scheduling threads is
   the sum of the base priority value and an increment (toward lower priority)
   derived from the thread's run time.
   .B param
   is the base priority value for the thread.
   
   .B POLICY_FIXEDPRI
   
   Fixed-priority threads run in order of their priorities, which range
   from 0 (highest) to 31 (lowest).  A thread may also be designated
   as round-robin or first-in-first-out.  The processor multiplexes between
   round-robin threads of equal priority at each quantum expiration.  In
   contrast, a first-in-first-out thread will run until it blocks, if no
   higher-priority threads are runnable.
   
   .B param
   has two components:  the thread's priority, and whether the thread
   is round-robin (TRUE) or first-in-first-out (FALSE).
   
   Processor sets may restrict the allowed policies, so this call will fail
   if the processor set to which 
   .B thread
   is currently assigned does not permit 
   .B policy.
   Moreover, the thread's processor set control port
   must be presented to allow changing the thread's policy, since
   a malfunctioning fixed-priority thread at priority 0 would prevent
   all other threads in the system from running.
   
   .SH DIAGNOSTICS
   .TP 25
   KERN_SUCCESS
   The call succeeded.
   .TP 25
   KERN_INVALID_ARGUMENT
   .B thread
   is not a thread, or
   .B policy
   is not a recognized policy, or
   .B pset
   is not the thread's current processor set.
   .TP 25
   KERN_FAILURE
   The processor set to which 
   .B thread
   is currently assigned does not permit 
   .B policy.
   
   .SH BUGS
   Availability limited.
   
   .SH SEE ALSO
   .B task_set_default_policy, processor_set_policy_add, host_info
   
   
   

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