CODEWITHSUNDEEP
c++language-lawyerstdmutex
Alex Guteniev
Alex Guteniev

Reputation: 13689

Why is std::mutex a standard-layout class?

[thread.mutex.class]/3:

[...] It is a standard-layout class ([class.prop]).

What is the reason for this requirement?

Upvotes: 13

Views: 470

Answers (1)

dfrib
dfrib

Reputation: 73196

Interoperability with the associated C interface. From N2320 (Multi-threading Library for Standard C++):

The C level interface has been removed from this proposal with the following rationale:

  • As long as we specify that the key types in this proposal are standard-layout types (which we have done), WG14 is still free to standardize a C interface which interoperates with this C++ interface.
  • WG14 is in a better position to solve the cancellation interoperability problem than WG21 is. [...]
  • WG14 asked WG21 to take the lead on this issue. We feel we can best take lead by specifying only a C++ interface which has the minimum hooks in it to support a future C interoperating interface (i.e. types are standard-layout types). We feel we should stop short of actually specifying that C interface in the C++ standard. WG14 can do a better job with the C interface and a future C++ standard can then import it by reference.

Upvotes: 12

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