__printf_lock and __printf_unlock

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Jerry Gardner

• October 15, 2014 07:35

The CrossWorks for ARM 3.2 documentation says that implementing these two functions is necessary to ensure mutual exclusion for printf and related functions.

If I define these two functions in my code (along with mutex lock/unlock code to enable exclusion), the linker complains that these functions are already defined (presumably in the Rowley C libraries).

How do I implement these functions in my code (which used an RTOS, so mutual exclusion is necessary) so that they don't conflict with the stub versions in the libraries?

 

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  Michael Johnson

  • October 15, 2014 07:38

  Set the "Use Multi Threaded Libraries" property to "Yes" - we need to rename this property.

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  Jerry Gardner

  • October 15, 2014 15:26

  When I set  "Use Multi Threaded Libraries" to "Yes", does that mean that I no longer need to implement __printf_lock and _unlock?

  When I set this property to "Yes" and define __printf_lock (and _unlock), they are discarded by the linker, presumably because nothing calls them.

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  Michael Johnson

  • October 15, 2014 15:36

  If you don't use printf/scanf then they won't be required - assuming you leave "Enable Unused Symbol Removal" set to "Yes".

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  Jerry Gardner

  • October 15, 2014 15:45

  I only use sprintf in my code, not printf/scanf. Based on your reply above, it looks like I don't need to implement mutual exclusion--is this correct? Is sprintf thread-safe without having to implement any specific mechanisms (like __printf_lock/unlock)?

  This came up because I'm having problems with bus errors happening in the library vfprintf code. My application runs under an RTOS, so thread safety is an issue.

   

   

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