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| <section id="task-scheduling-interfaces"> |
| <h1>Task Scheduling Interfaces<a class="headerlink" href="#task-scheduling-interfaces" title="Permalink to this heading"></a></h1> |
| <p>By default, NuttX performs strict priority scheduling: Tasks of higher |
| priority have exclusive access to the CPU until they become blocked. At |
| that time, the CPU is available to tasks of lower priority. Tasks of |
| equal priority are scheduled FIFO.</p> |
| <p>Optionally, a NuttX task or thread can be configured with round-robin or |
| <em>sporadic</em> scheduler. The round-robin is similar to priority scheduling |
| <em>except</em> that tasks with equal priority and share CPU time via |
| <em>time-slicing</em>. The time-slice interval is a constant determined by the |
| configuration setting <code class="docutils literal notranslate"><span class="pre">CONFIG_RR_INTERVAL</span></code> to a positive, non-zero |
| value. Sporadic scheduling scheduling is more complex, varying the |
| priority of a thread over a <em>replenishment</em> period. Support for sporadic |
| scheduling is enabled by the configuration option |
| <code class="docutils literal notranslate"><span class="pre">CONFIG_SCHED_SPORADIC</span></code>.</p> |
| <p>The OS interfaces described in the following paragraphs provide a POSIX- |
| compliant interface to the NuttX scheduler:</p> |
| <blockquote> |
| <div><ul class="simple"> |
| <li><p><a class="reference internal" href="#c.sched_setparam" title="sched_setparam"><code class="xref c c-func docutils literal notranslate"><span class="pre">sched_setparam()</span></code></a></p></li> |
| <li><p><a class="reference internal" href="#c.sched_getparam" title="sched_getparam"><code class="xref c c-func docutils literal notranslate"><span class="pre">sched_getparam()</span></code></a></p></li> |
| <li><p><a class="reference internal" href="#c.sched_setscheduler" title="sched_setscheduler"><code class="xref c c-func docutils literal notranslate"><span class="pre">sched_setscheduler()</span></code></a></p></li> |
| <li><p><a class="reference internal" href="#c.sched_getscheduler" title="sched_getscheduler"><code class="xref c c-func docutils literal notranslate"><span class="pre">sched_getscheduler()</span></code></a></p></li> |
| <li><p><a class="reference internal" href="#c.sched_yield" title="sched_yield"><code class="xref c c-func docutils literal notranslate"><span class="pre">sched_yield()</span></code></a></p></li> |
| <li><p><a class="reference internal" href="#c.sched_get_priority_max" title="sched_get_priority_max"><code class="xref c c-func docutils literal notranslate"><span class="pre">sched_get_priority_max()</span></code></a></p></li> |
| <li><p><a class="reference internal" href="#c.sched_get_priority_min" title="sched_get_priority_min"><code class="xref c c-func docutils literal notranslate"><span class="pre">sched_get_priority_min()</span></code></a></p></li> |
| <li><p><a class="reference internal" href="#c.sched_get_rr_interval" title="sched_get_rr_interval"><code class="xref c c-func docutils literal notranslate"><span class="pre">sched_get_rr_interval()</span></code></a></p></li> |
| </ul> |
| </div></blockquote> |
| <section id="functions"> |
| <h2>Functions<a class="headerlink" href="#functions" title="Permalink to this heading"></a></h2> |
| <dl class="c function"> |
| <dt class="sig sig-object c" id="c.sched_setparam"> |
| <span class="kt"><span class="pre">int</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">sched_setparam</span></span></span><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.pid_t" title="pid_t"><span class="n"><span class="pre">pid_t</span></span></a><span class="w"> </span><span class="n"><span class="pre">pid</span></span>, <span class="pre">FAR</span><span class="w"> </span><span class="k"><span class="pre">const</span></span><span class="w"> </span><span class="k"><span class="pre">struct</span></span><span class="w"> </span><a class="reference internal" href="structures.html#c.sched_param" title="sched_param"><span class="n"><span class="pre">sched_param</span></span></a><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">param</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.sched_setparam" title="Permalink to this definition"></a><br /></dt> |
| <dd><p>This function sets the priority of the task specified |
| by pid input parameter.</p> |
| <dl class="field-list simple"> |
| <dt class="field-odd">Parameters<span class="colon">:</span></dt> |
| <dd class="field-odd"><ul class="simple"> |
| <li><p><strong>pid</strong> – The task ID of the task. If <code class="docutils literal notranslate"><span class="pre">pid</span></code> is zero, the priority of |
| the calling task is set.</p></li> |
| <li><p><strong>param</strong> – A structure whose member <code class="docutils literal notranslate"><span class="pre">sched_priority</span></code> is the integer |
| priority. The range of valid priority numbers is from |
| <code class="docutils literal notranslate"><span class="pre">SCHED_PRIORITY_MIN</span></code> through <code class="docutils literal notranslate"><span class="pre">SCHED_PRIORITY_MAX</span></code>.</p></li> |
| </ul> |
| </dd> |
| <dt class="field-even">Returns<span class="colon">:</span></dt> |
| <dd class="field-even"><p><p>On success, sched_setparam() returns 0 (<code class="docutils literal notranslate"><span class="pre">OK</span></code>). On |
| error, -1 (<code class="docutils literal notranslate"><span class="pre">ERROR</span></code>) is returned, and <code class="docutils literal notranslate"><span class="pre">`errno</span></code> <#ErrnoAccess>`__ is |
| set appropriately.</p> |
| <ul class="simple"> |
| <li><p><code class="docutils literal notranslate"><span class="pre">EINVAL</span></code>. The parameter <code class="docutils literal notranslate"><span class="pre">param</span></code> is invalid or does not make sense |
| for the current scheduling policy.</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">EPERM</span></code>. The calling task does not have appropriate privileges.</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">ESRCH</span></code>. The task whose ID is <code class="docutils literal notranslate"><span class="pre">pid</span></code> could not be found.</p></li> |
| </ul> |
| </p> |
| </dd> |
| </dl> |
| <p><strong>POSIX Compatibility:</strong> Comparable to the POSIX interface of the same |
| name. Differences from the full POSIX implementation include:</p> |
| <blockquote> |
| <div><ul class="simple"> |
| <li><p>The range of priority values for the POSIX call is 0 to 255. The |
| priority 0 is the lowest priority and 255 is the highest priority.</p></li> |
| </ul> |
| </div></blockquote> |
| <div class="admonition note"> |
| <p class="admonition-title">Note</p> |
| <p>Setting a task’s priority to the same value has the similar effect |
| to <code class="docutils literal notranslate"><span class="pre">sched_yield()</span></code>: The task will be moved to after all other tasks |
| with the same priority.</p> |
| </div> |
| </dd></dl> |
| |
| <dl class="c function"> |
| <dt class="sig sig-object c" id="c.sched_getparam"> |
| <span class="kt"><span class="pre">int</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">sched_getparam</span></span></span><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.pid_t" title="pid_t"><span class="n"><span class="pre">pid_t</span></span></a><span class="w"> </span><span class="n"><span class="pre">pid</span></span>, <span class="pre">FAR</span><span class="w"> </span><span class="k"><span class="pre">struct</span></span><span class="w"> </span><a class="reference internal" href="structures.html#c.sched_param" title="sched_param"><span class="n"><span class="pre">sched_param</span></span></a><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">param</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.sched_getparam" title="Permalink to this definition"></a><br /></dt> |
| <dd><p>This function gets the scheduling priority of the task |
| specified by pid.</p> |
| <dl class="field-list simple"> |
| <dt class="field-odd">Parameters<span class="colon">:</span></dt> |
| <dd class="field-odd"><ul class="simple"> |
| <li><p><strong>pid</strong> – The task ID of the task. If pid is zero, the priority of the |
| calling task is returned.</p></li> |
| <li><p><strong>param</strong> – A structure whose member <code class="docutils literal notranslate"><span class="pre">sched_priority</span></code> is the integer |
| priority. The task’s priority is copied to the <code class="docutils literal notranslate"><span class="pre">sched_priority</span></code> |
| element of this structure.</p></li> |
| </ul> |
| </dd> |
| <dt class="field-even">Returns<span class="colon">:</span></dt> |
| <dd class="field-even"><p>0 (<code class="docutils literal notranslate"><span class="pre">OK</span></code>) if successful, otherwise -1 (<code class="docutils literal notranslate"><span class="pre">ERROR</span></code>).</p> |
| </dd> |
| </dl> |
| <p><strong>POSIX Compatibility:</strong> Comparable to the POSIX interface of the same |
| name.</p> |
| </dd></dl> |
| |
| <dl class="c function"> |
| <dt class="sig sig-object c" id="c.sched_setscheduler"> |
| <span class="kt"><span class="pre">int</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">sched_setscheduler</span></span></span><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.pid_t" title="pid_t"><span class="n"><span class="pre">pid_t</span></span></a><span class="w"> </span><span class="n"><span class="pre">pid</span></span>, <span class="kt"><span class="pre">int</span></span><span class="w"> </span><span class="n"><span class="pre">policy</span></span>, <span class="k"><span class="pre">const</span></span><span class="w"> </span><span class="k"><span class="pre">struct</span></span><span class="w"> </span><a class="reference internal" href="structures.html#c.sched_param" title="sched_param"><span class="n"><span class="pre">sched_param</span></span></a><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">param</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.sched_setscheduler" title="Permalink to this definition"></a><br /></dt> |
| <dd><p><code class="docutils literal notranslate"><span class="pre">sched_setscheduler()</span></code> sets both the scheduling |
| policy and the priority for the task identified by <code class="docutils literal notranslate"><span class="pre">pid</span></code>. If <code class="docutils literal notranslate"><span class="pre">pid</span></code> |
| equals zero, the scheduler of the calling thread will be set. The |
| parameter <code class="docutils literal notranslate"><span class="pre">param</span></code> holds the priority of the thread under the new |
| policy.</p> |
| <dl class="field-list simple"> |
| <dt class="field-odd">Parameters<span class="colon">:</span></dt> |
| <dd class="field-odd"><ul class="simple"> |
| <li><p><strong>pid</strong> – The task ID of the task. If <code class="docutils literal notranslate"><span class="pre">pid</span></code> is zero, the priority of |
| the calling task is set.</p></li> |
| <li><p><strong>policy</strong> – Scheduling policy requested (either <code class="docutils literal notranslate"><span class="pre">SCHED_FIFO</span></code> or |
| <code class="docutils literal notranslate"><span class="pre">SCHED_RR</span></code>).</p></li> |
| <li><p><strong>param</strong> – A structure whose member <code class="docutils literal notranslate"><span class="pre">sched_priority</span></code> is the integer |
| priority. The range of valid priority numbers is from |
| <code class="docutils literal notranslate"><span class="pre">SCHED_PRIORITY_MIN</span></code> through <code class="docutils literal notranslate"><span class="pre">SCHED_PRIORITY_MAX</span></code>.</p></li> |
| </ul> |
| </dd> |
| <dt class="field-even">Returns<span class="colon">:</span></dt> |
| <dd class="field-even"><p><p>On success, <code class="docutils literal notranslate"><span class="pre">sched_setscheduler()</span></code> returns <code class="docutils literal notranslate"><span class="pre">OK</span></code> |
| (zero). On error, <code class="docutils literal notranslate"><span class="pre">ERROR</span></code> (-1) is returned, and |
| <code class="docutils literal notranslate"><span class="pre">errno</span></code> is set appropriately:</p> |
| <ul class="simple"> |
| <li><p><code class="docutils literal notranslate"><span class="pre">EINVAL</span></code>: The scheduling <code class="docutils literal notranslate"><span class="pre">policy</span></code> is not one of the recognized |
| policies.</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">ESRCH</span></code>: The task whose ID is <code class="docutils literal notranslate"><span class="pre">pid</span></code> could not be found.</p></li> |
| </ul> |
| </p> |
| </dd> |
| </dl> |
| <p><strong>POSIX Compatibility:</strong> Comparable to the POSIX interface of the same |
| name.</p> |
| </dd></dl> |
| |
| <dl class="c function"> |
| <dt class="sig sig-object c" id="c.sched_getscheduler"> |
| <span class="kt"><span class="pre">int</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">sched_getscheduler</span></span></span><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.pid_t" title="pid_t"><span class="n"><span class="pre">pid_t</span></span></a><span class="w"> </span><span class="n"><span class="pre">pid</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.sched_getscheduler" title="Permalink to this definition"></a><br /></dt> |
| <dd><p><code class="docutils literal notranslate"><span class="pre">sched_getscheduler()</span></code> returns the scheduling policy |
| currently applied to the task identified by <code class="docutils literal notranslate"><span class="pre">pid</span></code>. If <code class="docutils literal notranslate"><span class="pre">pid</span></code> equals |
| zero, the policy of the calling process will be retrieved.</p> |
| <dl class="field-list simple"> |
| <dt class="field-odd">Parameters<span class="colon">:</span></dt> |
| <dd class="field-odd"><ul class="simple"> |
| <li><p><strong>pid</strong> – The task ID of the task to query. If <code class="docutils literal notranslate"><span class="pre">pid</span></code> is zero, the |
| calling task is queried.</p></li> |
| </ul> |
| </dd> |
| <dt class="field-even">Returns<span class="colon">:</span></dt> |
| <dd class="field-even"><p><p>On success, <code class="docutils literal notranslate"><span class="pre">sched_getscheduler()</span></code> returns the policy for the task |
| (either <code class="docutils literal notranslate"><span class="pre">SCHED_FIFO</span></code> or <code class="docutils literal notranslate"><span class="pre">SCHED_RR</span></code>). On error, <code class="docutils literal notranslate"><span class="pre">ERROR</span></code> (-1) is |
| returned, and <code class="docutils literal notranslate"><span class="pre">errno</span></code> is set appropriately:</p> |
| <ul class="simple"> |
| <li><p><code class="docutils literal notranslate"><span class="pre">ESRCH</span></code>: The task whose ID is pid could not be found.</p></li> |
| </ul> |
| </p> |
| </dd> |
| </dl> |
| <p><strong>POSIX Compatibility:</strong> Comparable to the POSIX interface of the same |
| name.</p> |
| </dd></dl> |
| |
| <dl class="c function"> |
| <dt class="sig sig-object c" id="c.sched_yield"> |
| <span class="kt"><span class="pre">int</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">sched_yield</span></span></span><span class="sig-paren">(</span><span class="kt"><span class="pre">void</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.sched_yield" title="Permalink to this definition"></a><br /></dt> |
| <dd><p>This function forces the calling task to give up the |
| CPU (only to other tasks at the same priority).</p> |
| <dl class="field-list simple"> |
| <dt class="field-odd">Returns<span class="colon">:</span></dt> |
| <dd class="field-odd"><p>0 (<code class="docutils literal notranslate"><span class="pre">OK</span></code>) or -1 (<code class="docutils literal notranslate"><span class="pre">ERROR</span></code>)</p> |
| </dd> |
| </dl> |
| <p><strong>POSIX Compatibility:</strong> Comparable to the POSIX interface of the same |
| name.</p> |
| </dd></dl> |
| |
| <dl class="c function"> |
| <dt class="sig sig-object c" id="c.sched_get_priority_max"> |
| <span class="kt"><span class="pre">int</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">sched_get_priority_max</span></span></span><span class="sig-paren">(</span><span class="kt"><span class="pre">int</span></span><span class="w"> </span><span class="n"><span class="pre">policy</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.sched_get_priority_max" title="Permalink to this definition"></a><br /></dt> |
| <dd><p>This function returns the value of the highest possible |
| task priority for a specified scheduling policy.</p> |
| <dl class="field-list simple"> |
| <dt class="field-odd">Parameters<span class="colon">:</span></dt> |
| <dd class="field-odd"><ul class="simple"> |
| <li><p><strong>policy</strong> – Scheduling policy requested.</p></li> |
| </ul> |
| </dd> |
| <dt class="field-even">Returns<span class="colon">:</span></dt> |
| <dd class="field-even"><p>The maximum priority value or -1 (<code class="docutils literal notranslate"><span class="pre">ERROR</span></code>).</p> |
| </dd> |
| </dl> |
| <p><strong>POSIX Compatibility:</strong> Comparable to the POSIX interface of the same |
| name.</p> |
| </dd></dl> |
| |
| <dl class="c function"> |
| <dt class="sig sig-object c" id="c.sched_get_priority_min"> |
| <span class="kt"><span class="pre">int</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">sched_get_priority_min</span></span></span><span class="sig-paren">(</span><span class="kt"><span class="pre">int</span></span><span class="w"> </span><span class="n"><span class="pre">policy</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.sched_get_priority_min" title="Permalink to this definition"></a><br /></dt> |
| <dd><p>This function returns the value of the lowest possible |
| task priority for a specified scheduling policy.</p> |
| <dl class="field-list simple"> |
| <dt class="field-odd">Parameters<span class="colon">:</span></dt> |
| <dd class="field-odd"><ul class="simple"> |
| <li><p><strong>policy</strong> – Scheduling policy requested.</p></li> |
| </ul> |
| </dd> |
| <dt class="field-even">Returns<span class="colon">:</span></dt> |
| <dd class="field-even"><p>The minimum priority value or -1 (<code class="docutils literal notranslate"><span class="pre">ERROR</span></code>)</p> |
| </dd> |
| </dl> |
| <p><strong>POSIX Compatibility:</strong> Comparable to the POSIX interface of the same |
| name.</p> |
| </dd></dl> |
| |
| <dl class="c function"> |
| <dt class="sig sig-object c" id="c.sched_get_rr_interval"> |
| <span class="kt"><span class="pre">int</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">sched_get_rr_interval</span></span></span><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.pid_t" title="pid_t"><span class="n"><span class="pre">pid_t</span></span></a><span class="w"> </span><span class="n"><span class="pre">pid</span></span>, <span class="k"><span class="pre">struct</span></span><span class="w"> </span><a class="reference internal" href="structures.html#c.timespec" title="timespec"><span class="n"><span class="pre">timespec</span></span></a><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">interval</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.sched_get_rr_interval" title="Permalink to this definition"></a><br /></dt> |
| <dd><p><code class="docutils literal notranslate"><span class="pre">sched_rr_get_interval()</span></code> writes the timeslice |
| interval for task identified by <code class="docutils literal notranslate"><span class="pre">pid</span></code> into the timespec structure |
| pointed to by <code class="docutils literal notranslate"><span class="pre">interval</span></code>. If pid is zero, the timeslice for the |
| calling process is written into ‘interval. The identified process should |
| be running under the SCHED_RR scheduling policy.’</p> |
| <dl class="field-list simple"> |
| <dt class="field-odd">Parameters<span class="colon">:</span></dt> |
| <dd class="field-odd"><ul class="simple"> |
| <li><p><strong>pid</strong> – The task ID of the task. If pid is zero, the priority of the |
| calling task is returned.</p></li> |
| <li><p><strong>interval</strong> – A structure used to return the time slice.</p></li> |
| </ul> |
| </dd> |
| <dt class="field-even">Returns<span class="colon">:</span></dt> |
| <dd class="field-even"><p><p>On success, sched_rr_get_interval() returns OK (0). |
| On error, ERROR (-1) is returned, and <code class="docutils literal notranslate"><span class="pre">errno</span></code> is |
| set to:</p> |
| <ul class="simple"> |
| <li><p><code class="docutils literal notranslate"><span class="pre">EFAULT</span></code>: Cannot copy to interval</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">EINVAL</span></code>: Invalid pid.</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">ENOSYS</span></code>: The system call is not yet implemented.</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">ESRCH</span></code>: The process whose ID is pid could not be found.</p></li> |
| </ul> |
| </p> |
| </dd> |
| </dl> |
| <p><strong>POSIX Compatibility:</strong> Comparable to the POSIX interface of the same |
| name.</p> |
| </dd></dl> |
| |
| </section> |
| </section> |
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