gcc: Do I need -D_REENTRANT with pthreads?

Posted by stefanB on Stack Overflow See other posts from Stack Overflow or by stefanB
Published on 2009-05-18T00:01:21Z Indexed on 2010/03/11 20:29 UTC
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linux

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pthreads

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gcc

On Linux (kernel 2.6.5) our build system calls gcc with -D_REENTRANT.

Is this still required when using pthreads?

How is it related to gcc -pthread option? I understand that I should use -pthread with pthreads, do I still need -D_REENTRANT?

On a side note, is there any difference that you know off between the usage of REENTRANT between gcc 3.3.3 and gcc 4.x.x ?

When I use -pthread gcc option I can see that _REENTRANT gets defined. Will omitting -D_REENTRANT from command line make any difference, for example could some objects be compiled without multithreaded support and then linked into binary that uses pthreads and will cause problems?

I assume it should be ok just to use: g++ -pthread

> echo | g++          -E -dM -c - > singlethreaded
> echo | g++ -pthread -E -dM -c - > multithreaded
> diff singlethreaded multithreaded
39a40
> #define _REENTRANT 1

We're compiling multiple static libraries and applications that link with the static libraries, both libraries and application use pthreads.

I believe it was required at some stage in the past but want to know if it is still required. Googling hasn't returned any recent information mentioning -D_REENTRANT with pthreads. Could you point me to links or references discussing the use in recent version of kernel/gcc/pthread?

Clarification: At the moment we're using -D_REENTRANT and -lpthread, I assume I can replace them with just g++ -pthread, looking at man gcc it sets the flags for both preprocessor and linker. Any thoughts?

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