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How to use errno in multithread environment?


The traditional 'errno' global variable is not safe in multithreading environment. From errno.h, I figure out it should be possible to define the _Geterrno() function to use different errno variables for each thread. My question is: how can I do that?

Any suggestion is welcome, thanks.

  • Which compiler do you use?  What version?

    Thanks and regards,


  • Hi George:

    I am using TI C/C++ Compile for ARM. I also updated it to the last version in CCS.

  • The function _Geterrno was never really supported in the RTS library provided with the TI ARM compiler, and it has been removed in the latest version. I do not recommend you start using it now.

    The TI ARM compiler doesn't really support thread-local storage, although the ARM EABI does.

    The ARM EABI defines the function __aeabi_errno_addr, which does essentially the same thing. When compiling in EABI mode when _AEABI_PORTABILITY_LEVEL has a non-zero value, use errno as you normally would, and what you'll really get is a call to this function. However, in order to get a truly thread-local errno, you will need some additional support from the RTS and the linker. You'll have to recompile the TI RTS with _AEABI_PORTABILITY_LEVEL=1 so that functions which access errno will use __aeabi_errno_addr. I'm not sure whether you can use the TI ARM linker as-is, but I suspect you can. In any case, you would probably be better off using another vendor's linker.
  • Hi Archaeologist,

    Thanks for your kindly reply.

    It looks like it is better to not use errno at all. I will keep this in mind.