Named mutex might not value permissions correctly

Hi!

When using a named_mutex within POSIX, and setting the Permissions Object, everything boils down to an ::sem_open call. There, the permissions are passed. But ::sem_open masks the permissions with the processes umask. Therefore, the semaphore might not have 0666 permissions, but e.g. 644, even though, permissions were passed with set_unrestricted().

Workaround there would be setting umask to 0 before ::sem_open, and restoring again after.
At least, this behaviour should be documented.

Regards,

Matthias

まず、issue で説明されている ::sem_open 呼び出しまで POSIX named_mutex の経路を追跡し、Permissions Object の値がプロセスの umask とどのように相互作用するかに注目します。set_unrestricted() で結果として得られる権限を確認し、意図した結果が動作の変更なのか、それとも制限の文書化なのかを判断します。

索引モデルが issue の本文から書いたものです。