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<!-- Copyright (C) 2003 Red Hat, Inc. --> <!-- This material may be distributed only subject to the terms --> <!-- and conditions set forth in the Open Publication License, v1.0 --> <!-- or later (the latest version is presently available at --> <!-- http://www.opencontent.org/openpub/). --> <!-- Distribution of the work or derivative of the work in any --> <!-- standard (paper) book form is prohibited unless prior --> <!-- permission is obtained from the copyright holder. --> <HTML ><HEAD ><TITLE >Thread safety</TITLE ><meta name="MSSmartTagsPreventParsing" content="TRUE"> <META NAME="GENERATOR" CONTENT="Modular DocBook HTML Stylesheet Version 1.76b+ "><LINK REL="HOME" TITLE="eCos Reference Manual" HREF="ecos-ref.html"><LINK REL="UP" TITLE="C and math library overview" HREF="c-and-math-library-overview.html"><LINK REL="PREVIOUS" TITLE="Some implementation details" HREF="libc-implementation-details.html"><LINK REL="NEXT" TITLE="C library startup" HREF="c-library-startup.html"></HEAD ><BODY CLASS="SECT1" BGCOLOR="#FFFFFF" TEXT="#000000" LINK="#0000FF" VLINK="#840084" ALINK="#0000FF" ><DIV CLASS="NAVHEADER" ><TABLE SUMMARY="Header navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TH COLSPAN="3" ALIGN="center" >eCos Reference Manual</TH ></TR ><TR ><TD WIDTH="10%" ALIGN="left" VALIGN="bottom" ><A HREF="libc-implementation-details.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="80%" ALIGN="center" VALIGN="bottom" >Chapter 13. C and math library overview</TD ><TD WIDTH="10%" ALIGN="right" VALIGN="bottom" ><A HREF="c-library-startup.html" ACCESSKEY="N" >Next</A ></TD ></TR ></TABLE ><HR ALIGN="LEFT" WIDTH="100%"></DIV ><DIV CLASS="SECT1" ><H1 CLASS="SECT1" ><A NAME="LIBC-THREAD-SAFETY">Thread safety</H1 ><P >The ISO C library has configuration options that control thread safety, i.e. working behavior if multiple threads call the same function at the same time.</P ><P >The following functionality has to be configured correctly, or used carefully in a multi-threaded environment:</P ><P ></P ><UL ><LI ><P ><TT CLASS="FUNCTION" >mblen()</TT ></P ></LI ><LI ><P ><TT CLASS="FUNCTION" >mbtowc()</TT ></P ></LI ><LI ><P ><TT CLASS="FUNCTION" >wctomb()</TT ></P ></LI ><LI ><P ><TT CLASS="FUNCTION" >printf()</TT > (and all standard I/O functions except for <TT CLASS="FUNCTION" >sprintf()</TT > and <TT CLASS="FUNCTION" >sscanf()</TT ></P ></LI ><LI ><P ><TT CLASS="FUNCTION" >strtok()</TT ></P ></LI ><LI ><P ><TT CLASS="FUNCTION" >rand()</TT > and <TT CLASS="FUNCTION" >srand()</TT ></P ></LI ><LI ><P ><TT CLASS="FUNCTION" >signal()</TT > and <TT CLASS="FUNCTION" >raise()</TT ></P ></LI ><LI ><P ><TT CLASS="FUNCTION" >asctime()</TT > , <TT CLASS="FUNCTION" >ctime()</TT > , <TT CLASS="FUNCTION" >gmtime()</TT > , and <TT CLASS="FUNCTION" >localtime()</TT ></P ></LI ><LI ><P >the <TT CLASS="FUNCTION" >errno</TT > variable</P ></LI ><LI ><P >the <TT CLASS="FUNCTION" >environ</TT > variable</P ></LI ><LI ><P >date and time settings</P ></LI ></UL ><P >In some cases, to make <SPAN CLASS="emphasis" ><I CLASS="EMPHASIS" >eCos</I ></SPAN > development easier, functions are provided (as specified by POSIX 1003.1) that define re-entrant alternatives, i.e. <TT CLASS="FUNCTION" >rand_r()</TT >, <TT CLASS="FUNCTION" >strtok_r()</TT >, <TT CLASS="FUNCTION" >asctime_r()</TT >, <TT CLASS="FUNCTION" >ctime_r()</TT >, <TT CLASS="FUNCTION" >gmtime_r()</TT >, and <TT CLASS="FUNCTION" >localtime_r()</TT >. In other cases, configuration options are provided that control either locking of functions or their shared data, such as with standard I/O streams, or by using per-thread data, such as with the <TT CLASS="FUNCTION" >errno</TT > variable.</P ><P >In some other cases, like the setting of date and time, no re-entrant or thread-safe alternative or configuration is provided as it is simply not a worthwhile addition (date and time should rarely need to be set.)</P ></DIV ><DIV CLASS="NAVFOOTER" ><HR ALIGN="LEFT" WIDTH="100%"><TABLE SUMMARY="Footer navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" ><A HREF="libc-implementation-details.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="ecos-ref.html" ACCESSKEY="H" >Home</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" ><A HREF="c-library-startup.html" ACCESSKEY="N" >Next</A ></TD ></TR ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" >Some implementation details</TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="c-and-math-library-overview.html" ACCESSKEY="U" >Up</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" >C library startup</TD ></TR ></TABLE ></DIV ></BODY ></HTML >