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<!-- Copyright (C) 2003 Red Hat, Inc.                                -->
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NAME="KERNEL-THREAD-PRIORITIES">Thread priorities</H1
><DIV
CLASS="REFNAMEDIV"
><A
NAME="AEN616"
></A
><H2
>Name</H2
>cyg_thread_get_priority, cyg_thread_get_current_priority, cyg_thread_set_priority&nbsp;--&nbsp;Examine and manipulate thread priorities</DIV
><DIV
CLASS="REFSYNOPSISDIV"
><A
NAME="AEN621"><H2
>Synopsis</H2
><DIV
CLASS="FUNCSYNOPSIS"
><A
NAME="AEN622"><P
></P
><TABLE
BORDER="5"
BGCOLOR="#E0E0F0"
WIDTH="70%"
><TR
><TD
><PRE
CLASS="FUNCSYNOPSISINFO"
>#include &lt;cyg/kernel/kapi.h&gt;
        </PRE
></TD
></TR
></TABLE
><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
><P
></P
></DIV
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN641"
></A
><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.
      </P
></DIV
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1	28	unneback	`<!-- Copyright (C) 2003 Red Hat, Inc. -->`
2			`<!-- This material may be distributed only subject to the terms -->`
3			`<!-- and conditions set forth in the Open Publication License, v1.0 -->`
4			`<!-- or later (the latest version is presently available at -->`
5			`<!-- http://www.opencontent.org/openpub/). -->`
6			`<!-- Distribution of the work or derivative of the work in any -->`
7			`<!-- standard (paper) book form is prohibited unless prior -->`
8			`<!-- permission is obtained from the copyright holder. -->`
9			`<HTML`
10			`><HEAD`
11			`><TITLE`
12			`>Thread priorities</TITLE`
13			`><meta name="MSSmartTagsPreventParsing" content="TRUE">`
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25			`TITLE="Thread termination"`
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27			`REL="NEXT"`
28			`TITLE="Per-thread data"`
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47			`COLSPAN="3"`
48			`ALIGN="center"`
49			`>eCos Reference Manual</TH`
50			`></TR`
51			`><TR`
52			`><TD`
53			`WIDTH="10%"`
54			`ALIGN="left"`
55			`VALIGN="bottom"`
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58			`ACCESSKEY="P"`
59			`>Prev</A`
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82			`NAME="KERNEL-THREAD-PRIORITIES">Thread priorities</H1`
83			`><DIV`
84			`CLASS="REFNAMEDIV"`
85			`><A`
86			`NAME="AEN616"`
87			`></A`
88			`><H2`
89			`>Name</H2`
90			`>cyg_thread_get_priority, cyg_thread_get_current_priority, cyg_thread_set_priority -- Examine and manipulate thread priorities</DIV`
91			`><DIV`
92			`CLASS="REFSYNOPSISDIV"`
93			`><A`
94			`NAME="AEN621"><H2`
95			`>Synopsis</H2`
96			`><DIV`
97			`CLASS="FUNCSYNOPSIS"`
98			`><A`
99			`NAME="AEN622"><P`
100			`></P`
101			`><TABLE`
102			`BORDER="5"`
103			`BGCOLOR="#E0E0F0"`
104			`WIDTH="70%"`
105			`><TR`
106			`><TD`
107			`><PRE`
108			`CLASS="FUNCSYNOPSISINFO"`
109			`>#include <cyg/kernel/kapi.h>`
110			`</PRE`
111			`></TD`
112			`></TR`
113			`></TABLE`
114			`><P`
115			`><CODE`
116			`><CODE`
117			`CLASS="FUNCDEF"`
118			`>cyg_priority_t cyg_thread_get_priority</CODE`
119			`>(cyg_handle_t thread);</CODE`
120			`></P`
121			`><P`
122			`><CODE`
123			`><CODE`
124			`CLASS="FUNCDEF"`
125			`>cyg_priority_t cyg_thread_get_current_priority</CODE`
126			`>(cyg_handle_t thread);</CODE`
127			`></P`
128			`><P`
129			`><CODE`
130			`><CODE`
131			`CLASS="FUNCDEF"`
132			`>void cyg_thread_set_priority</CODE`
133			`>(cyg_handle_t thread, cyg_priority_t priority);</CODE`
134			`></P`
135			`><P`
136			`></P`
137			`></DIV`
138			`></DIV`
139			`><DIV`
140			`CLASS="REFSECT1"`
141			`><A`
142			`NAME="AEN641"`
143			`></A`
144			`><H2`
145			`>Description</H2`
146			`><P`
147			`>Typical schedulers use the concept of a thread priority to determine`
148			`which thread should run next. Exactly what this priority consists of`
149			`will depend on the scheduler, but a typical implementation would be a`
150			`small integer in the range 0 to 31, with 0 being the highest priority.`
151			`Usually only the idle thread will run at the lowest priority. The`
152			`exact number of priority levels available depends on the`
153			`configuration, typically the option`
154			`<TT`
155			`CLASS="VARNAME"`
156			`>CYGNUM_KERNEL_SCHED_PRIORITIES</TT`
157			`>.`
158			`</P`
159			`><P`
160			`><TT`
161			`CLASS="FUNCTION"`
162			`>cyg_thread_get_priority</TT`
163			`> can be used to determine`
164			`the priority of a thread, or more correctly the value last used in a`
165			`<TT`
166			`CLASS="FUNCTION"`
167			`>cyg_thread_set_priority</TT`
168			`> call or when the thread`
169			`was first created. In some circumstances it is possible that the`
170			`thread is actually running at a higher priority. For example, if it`
171			`owns a mutex and priority ceilings or inheritance is being used to`
172			`prevent priority inversion problems, then the thread's priority may`
173			`have been boosted temporarily.`
174			`<TT`
175			`CLASS="FUNCTION"`
176			`>cyg_thread_get_current_priority</TT`
177			`> returns the real`
178			`current priority.`
179			`</P`
180			`><P`
181			`>In many applications appropriate thread priorities can be determined`
182			`and allocated statically. However, if it is necessary for a thread's`
183			`priority to change at run-time then the`
184			`<TT`
185			`CLASS="FUNCTION"`
186			`>cyg_thread_set_priority</TT`
187			`> function provides this`
188			`functionality.`
189			`</P`
190			`></DIV`
191			`><DIV`
192			`CLASS="REFSECT1"`
193			`><A`
194			`NAME="KERNEL-THREAD-PRIORITIES-CONTEXT"`
195			`></A`
196			`><H2`
197			`>Valid contexts</H2`
198			`><P`
199			`><TT`
200			`CLASS="FUNCTION"`
201			`>cyg_thread_get_priority</TT`
202			`> and`
203			`<TT`
204			`CLASS="FUNCTION"`
205			`>cyg_thread_get_current_priority</TT`
206			`> can be called`
207			`from thread or DSR context, although the latter is rarely useful.`
208			`<TT`
209			`CLASS="FUNCTION"`
210			`>cyg_thread_set_priority</TT`
211			`> should also only be`
212			`called from thread context.`
213			`</P`
214			`></DIV`
215			`><DIV`
216			`CLASS="NAVFOOTER"`
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242			`>Home</A`
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259			`>Thread termination</TD`
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279			`>`

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