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

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    .\" HISTORY
    .\" $Log:       thread_priority.man,v $
    .\" Revision 2.4  91/05/14  17:14:19  mrt
    .\"     Correcting copyright
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    .\" Revision 2.3  91/02/14  14:15:25  mrt
    .\"     Changed to new Mach copyright
    .\"     [91/02/12  18:16:18  mrt]
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    .\" Revision 2.2  90/08/07  18:46:13  rpd
    .\"     Created.
    .\" 
    .TH thread_priority 2 8/13/89
    .CM 4
    .SH NAME
    .nf
    thread_priority  \-  set scheduling priority for thread
    thread_max_priority  \-  set max scheduling priority for thread
    .SH SYNOPSIS
    .nf
    .ft B
    #include <mach.h>
    
    .nf
    .ft B
    kern_return_t thread_priority(thread, priority, set_max)
            thread_t        thread;
            int             priority;
            boolean_t       set_max
    
    
    .fi
    .ft P
    .nf
    .ft B
    kern_return_t thread_max_priority(thread, processor_set, priority)
            thread_t        thread;
            processor_set_t processor_set;
            int             priority;
    
    
    .fi
    .ft P
    .SH ARGUMENTS
    .TP 15
    .B
    thread
    The thread whose priority is to be changed.
    .TP 15
    .B
    priority
    The new priority to change it to.
    .TP 15
    .B
    set_max
    Also set thread's maximum priority if TRUE.
    .TP 15
    .B
    processor_set
    The control port for the processor set to which the 
    thread is currently assigned.
    
    .SH DESCRIPTION
    Threads have three priorities associated with them by the system, a
    .B priority
    , a 
    .B maximum priority
    , and a 
    .B scheduled priority.
    The scheduled priority is used to make scheduling decisions about the
    thread.  It is determined from the priority by the policy (for timesharing,
    this means adding an increment derived from cpu usage).  The priority
    can be set under user control, but may never exceed the maximum priority.
   Changing the maximum priority requires presentation of the control port
   for the thread's processor set; since the control port for the default
   processor set is privileged, users cannot raise their maximum priority
   to unfairly compete with other users on that set.  Newly created threads
   obtain their priority from their task and their max priority from the
   thread.
   
   .B thread_priority
   changes the priority and optionally the maximum priority of
   .B thread.
   Priorities range from 0 to 31, where lower numbers denote higher
   priorities.  If the new priority is higher than the priority of the
   current thread, preemption may occur as a result of this call.
   The maximum priority of the thread is also set if 
   .B set_max
   is TRUE.  This call will fail if 
   .B priority
   is greater than the current maximum priority of the thread.  As a result,
   this call can only lower the value of a thread's maximum priority.
   
   .B thread_max_priority
   changes the maximum priority of the thread.  Because it requires
   presentation of the corresponding processor set port, this call can reset
   the maximum priority to any legal value.
   
   .SH DIAGNOSTICS
   .TP 25
   KERN_SUCCESS
   Operation completed successfully
   .TP 25
   KERN_INVALID_ARGUMENT
   .B thread
   is not a thread, or
   .B processor_set
   is not a control port for a processor set, or
   .B priority
   is out of range (not in 0..31).
   .TP 25
   KERN_FAILURE
   The requested operation would violate the thread's 
   maximum priority
   (thread_priority) or the thread is not assigned to the processor set
   whose control port was presented.
   
   .SH BUGS
   Availability limited.
   
   .SH SEE ALSO
   .B thread_policy, task_priority, processor_set_priority
   

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