Are function static variables thread-safe in GCC?

user_140006 0
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In the example code

void foo()
{
  static Bar b;
  ...
}

compiled with GCC is it guaranteed that b will be created and initialized in a thread-safe manner ?

In gcc's man page, found the -fno-threadsafe-statics command line option:

Do not emit the extra code to use the routines specified in the C++ ABI for thread-safe initialization of local statics. You can use this option to reduce code size slightly in code that doesn't need to be thread-safe.

  1. Does it mean, that local statics are thread-safe by default with GCC ? So no reason to put explicit guarding e.g. with pthread_mutex_lock/unlock ?

  2. How to write portable code - how to check if compiler will add its guards ? Or is it better to turn off this feature of GCC ?

thread-safety initialization static gcc c++
4 Answers

  1. No, it means that the initialization of local statics is thread-safe.

  2. You definitely want to leave this feature enabled. Thread-safe initialization of local statics is very important. If you need generally thread-safe access to local statics then you will need to add the appropriate guards yourself.

Charles_Bailey_195630

This is not really answering your questions straight away (Charles already did that), but I think it's time to post a link to this article again. It throws light on the initialization of globals and should be read and understood by everyone attempting to use static variables in a multi-threaded environment.

user_1407190

I think that the key phrase is

... thread-safe initialization of local statics.

I read this as meaning that it is only initialization of statics that would be done in a thread-safe way. General use of statics would not be thread-safe.

user_1399850
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