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><H1
><A
NAME="KERNEL-THREAD-PRIORITIES">Thread priorities</H1
><DIV
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><A
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><H2
>Name</H2
>cyg_thread_get_priority, cyg_thread_get_current_priority, cyg_thread_set_priority -- Examine and manipulate thread priorities</DIV
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><PRE
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>#include <cyg/kernel/kapi.h>
</PRE
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><P
><CODE
><CODE
CLASS="FUNCDEF"
>cyg_priority_t cyg_thread_get_priority</CODE
>(cyg_handle_t thread);</CODE
></P
><P
><CODE
><CODE
CLASS="FUNCDEF"
>cyg_priority_t cyg_thread_get_current_priority</CODE
>(cyg_handle_t thread);</CODE
></P
><P
><CODE
><CODE
CLASS="FUNCDEF"
>void cyg_thread_set_priority</CODE
>(cyg_handle_t thread, cyg_priority_t priority);</CODE
></P
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><H2
>Description</H2
><P
>Typical schedulers use the concept of a thread priority to determine
which thread should run next. Exactly what this priority consists of
will depend on the scheduler, but a typical implementation would be a
small integer in the range 0 to 31, with 0 being the highest priority.
Usually only the idle thread will run at the lowest priority. The
exact number of priority levels available depends on the
configuration, typically the option
<TT
CLASS="VARNAME"
>CYGNUM_KERNEL_SCHED_PRIORITIES</TT
>.
</P
><P
><TT
CLASS="FUNCTION"
>cyg_thread_get_priority</TT
> can be used to determine
the priority of a thread, or more correctly the value last used in a
<TT
CLASS="FUNCTION"
>cyg_thread_set_priority</TT
> call or when the thread
was first created. In some circumstances it is possible that the
thread is actually running at a higher priority. For example, if it
owns a mutex and priority ceilings or inheritance is being used to
prevent priority inversion problems, then the thread's priority may
have been boosted temporarily.
<TT
CLASS="FUNCTION"
>cyg_thread_get_current_priority</TT
> returns the real
current priority.
</P
><P
>In many applications appropriate thread priorities can be determined
and allocated statically. However, if it is necessary for a thread's
priority to change at run-time then the
<TT
CLASS="FUNCTION"
>cyg_thread_set_priority</TT
> function provides this
functionality.
</P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="KERNEL-THREAD-PRIORITIES-CONTEXT"
></A
><H2
>Valid contexts</H2
><P
><TT
CLASS="FUNCTION"
>cyg_thread_get_priority</TT
> and
<TT
CLASS="FUNCTION"
>cyg_thread_get_current_priority</TT
> can be called
from thread or DSR context, although the latter is rarely useful.
<TT
CLASS="FUNCTION"
>cyg_thread_set_priority</TT
> should also only be
called from thread context.
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