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Comment by Sprocklem | Hacker News Reader

I was suggesting that the buffer be invalidated by each subsequent call – like some other libc functions' internal buffers – although, as I noted in the edit this would need `getenv()` to be able to indicate errors (specifically ENOMEM). It currently cannot do this as currently described, because NULL is used to indicate an absent variable.

You could also require callers free the returned memory when they're done, but that would be another change of API.

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> I was suggesting that the buffer be invalidated by each subsequent call

This would break very simple single-threaded programs that e.g. print two env vars in one printf call.

The solution to all problems like this was decided years ago: _r
You provide the storage and free it

The problem is these non-direct uses. They each need to switch to •_r and manage the buffer, or offer _r versions themselves and sort of pass through the problem

Of course, *_r is a better option, but the existing API is used so pervasively that it needs to be made thread-safe to actually avoid thread-unsafe code in, e.g, libraries.

I don’t see how you can make:

- return a pointer - the library owns the allocation - the state is global and mutable

Thread safe

A number of libc functions return a pointer to an internal thread-local buffer, which is invalidated on subsequent calls. If the function copies the environment variable's value to such a buffer while holding the mutex controlling access to the global state, then the returned value is guaranteed to remain unaffected by other threads.

There are, however, other problems (discussed elsewhere in this thread) that complicate such an API in the context of getenv().

Requiring you to hold a mutex to safely call the function is an API change

I was not suggesting the caller hold a mutex, but rather getenv(), which eould be transparent to the caller.

Don’t you need C++11?

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