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<title>WCSLIB 4.8.2: Thread-safety</title>
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<h1><a class="anchor" name="threads">Thread-safety </a></h1>With the following exceptions WCSLIB 4.8 is thread-safe:<p>
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<li>The C code generated by Flex is not re-entrant. Flex does have the capacity for producing re-entrant scanners but they have a different API. This may be handled by a compile-time option in future but in the meantime calls to the header parsers should be serialized via a mutex.</li></ul>
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<li>The low-level functions <a class="el" href="wcs_8h.html#42b2578d76ace7ca6114d82b7ae46a89" title="Memory allocation for PVi_ma.">wcsnpv()</a> and <a class="el" href="wcs_8h.html#e790c9ce6c9b7a4845cf1c3c97b1e97a" title="Memory allocation for PSi_ma.">wcsnps()</a> are not thread-safe but within the library itself they are only used by the Flex scanners <a class="el" href="wcshdr_8h.html#c75623ee805ab7d43b0bba684c719a60" title="FITS WCS parser routine for image headers.">wcspih()</a> and <a class="el" href="wcshdr_8h.html#dc053d80a9c4da454a52eed34e123633" title="FITS WCS parser routine for binary table and image headers.">wcsbth()</a>. They would rarely need to be used by application programmers.</li></ul>
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<li>Diagnostic functions that print the contents of the various structs, namely <a class="el" href="cel_8h.html#db2e4565f61a9de5fe278d9035850dc3" title="Print routine for the celprm struct.">celprt()</a>, <a class="el" href="lin_8h.html#946005b038f5c584691630b5d39369e3" title="Print routine for the linprm struct.">linprt()</a>, <a class="el" href="prj_8h.html#8785bdf33bdaa3d9d52fd51b621ec8d5" title="Print routine for the prjprm struct.">prjprt()</a>, <a class="el" href="spc_8h.html#7304d0d00bcf9d2bad1f56ba6d8322ea" title="Print routine for the spcprm struct.">spcprt()</a>, <a class="el" href="tab_8h.html#6b3768349e9a5e925aab24effddc584f" title="Print routine for the tabprm struct.">tabprt()</a>, <a class="el" href="wcs_8h.html#b9aeb8cf1afb1bfb22e989580d90fca8" title="Print routine for the wcsprm struct.">wcsprt()</a>, and <a class="el" href="wcs_8h.html#8fe5dcd9927240dc0348b850ee662367" title="Print error messages from a wcsprm struct.">wcsperr()</a> use printf() which is thread-safe by the POSIX requirement on <code>stdio</code>. However, this is only at the function level. Where multiple threads invoke these functions simultaneously their output is likely to be interleaved.</li></ul>
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<li><a class="el" href="wcserr_8h.html#1691b8bd184d40ca6fda255be078fa53" title="Enable/disable error messaging.">wcserr_enable()</a> sets a static variable and so is not thread-safe. However, this facility is not intended to be used dynamically. If detailed error messages are required, enable <a class="el" href="structwcserr.html" title="Error message handling.">wcserr</a> when execution starts and don't change it. </li></ul>
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