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<a name="Environment-Variables"></a>
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<p>
Next: <a href="Enabling-OpenACC.html#Enabling-OpenACC" accesskey="n" rel="next">Enabling OpenACC</a>, Previous: <a href="Runtime-Library-Routines.html#Runtime-Library-Routines" accesskey="p" rel="prev">Runtime Library Routines</a>, Up: <a href="index.html#Top" accesskey="u" rel="up">Top</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Library-Index.html#Library-Index" title="Index" rel="index">Index</a>]</p>
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<hr>
<a name="Environment-Variables-1"></a>
<h2 class="chapter">3 Environment Variables</h2>

<p>The environment variables which beginning with <code>OMP_</code> are defined by
section 4 of the OpenMP specification in version 4.5, while those
beginning with <code>GOMP_</code> are GNU extensions.
</p>
<table class="menu" border="0" cellspacing="0">
<tr><td align="left" valign="top">&bull; <a href="OMP_005fCANCELLATION.html#OMP_005fCANCELLATION" accesskey="1">OMP_CANCELLATION</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Set whether cancellation is activated
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="OMP_005fDISPLAY_005fENV.html#OMP_005fDISPLAY_005fENV" accesskey="2">OMP_DISPLAY_ENV</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Show OpenMP version and environment variables
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="OMP_005fDEFAULT_005fDEVICE.html#OMP_005fDEFAULT_005fDEVICE" accesskey="3">OMP_DEFAULT_DEVICE</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Set the device used in target regions
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="OMP_005fDYNAMIC.html#OMP_005fDYNAMIC" accesskey="4">OMP_DYNAMIC</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Dynamic adjustment of threads
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="OMP_005fMAX_005fACTIVE_005fLEVELS.html#OMP_005fMAX_005fACTIVE_005fLEVELS" accesskey="5">OMP_MAX_ACTIVE_LEVELS</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Set the maximum number of nested parallel regions
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="OMP_005fMAX_005fTASK_005fPRIORITY.html#OMP_005fMAX_005fTASK_005fPRIORITY" accesskey="6">OMP_MAX_TASK_PRIORITY</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Set the maximum task priority value
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="OMP_005fNESTED.html#OMP_005fNESTED" accesskey="7">OMP_NESTED</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Nested parallel regions
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="OMP_005fNUM_005fTHREADS.html#OMP_005fNUM_005fTHREADS" accesskey="8">OMP_NUM_THREADS</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Specifies the number of threads to use
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="OMP_005fPROC_005fBIND.html#OMP_005fPROC_005fBIND" accesskey="9">OMP_PROC_BIND</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Whether theads may be moved between CPUs
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="OMP_005fPLACES.html#OMP_005fPLACES">OMP_PLACES</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Specifies on which CPUs the theads should be placed
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="OMP_005fSTACKSIZE.html#OMP_005fSTACKSIZE">OMP_STACKSIZE</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Set default thread stack size
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="OMP_005fSCHEDULE.html#OMP_005fSCHEDULE">OMP_SCHEDULE</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">How threads are scheduled
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="OMP_005fTHREAD_005fLIMIT.html#OMP_005fTHREAD_005fLIMIT">OMP_THREAD_LIMIT</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Set the maximum number of threads
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="OMP_005fWAIT_005fPOLICY.html#OMP_005fWAIT_005fPOLICY">OMP_WAIT_POLICY</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">How waiting threads are handled
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="GOMP_005fCPU_005fAFFINITY.html#GOMP_005fCPU_005fAFFINITY">GOMP_CPU_AFFINITY</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Bind threads to specific CPUs
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="GOMP_005fDEBUG.html#GOMP_005fDEBUG">GOMP_DEBUG</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Enable debugging output
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="GOMP_005fSTACKSIZE.html#GOMP_005fSTACKSIZE">GOMP_STACKSIZE</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Set default thread stack size
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="GOMP_005fSPINCOUNT.html#GOMP_005fSPINCOUNT">GOMP_SPINCOUNT</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Set the busy-wait spin count
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="GOMP_005fRTEMS_005fTHREAD_005fPOOLS.html#GOMP_005fRTEMS_005fTHREAD_005fPOOLS">GOMP_RTEMS_THREAD_POOLS</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Set the RTEMS specific thread pools
</td></tr>
</table>


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Next: <a href="Enabling-OpenACC.html#Enabling-OpenACC" accesskey="n" rel="next">Enabling OpenACC</a>, Previous: <a href="Runtime-Library-Routines.html#Runtime-Library-Routines" accesskey="p" rel="prev">Runtime Library Routines</a>, Up: <a href="index.html#Top" accesskey="u" rel="up">Top</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Library-Index.html#Library-Index" title="Index" rel="index">Index</a>]</p>
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