On Fedora 28, creating an instance of `std::random_device` opens a file
descriptor for `/dev/urandom` (observed via `strace`).
By declaring static thread-local instances of `std::random_device`,
these descriptors will be open (barring optimization by the compiler)
for the entire duration of the Scylla process's life.
However, the `std::random_device` instance is only necessary for
initializing the `RandomNumberEngine` for generating salts. With this
change, the file-descriptor is closed immediately after the engine is
initialized.
I considered generalizing this pattern of initialization into a
function, but with only two uses (and simple ones) I think this would
only obscure things.
Signed-off-by: Jesse Haber-Kucharsky <jhaberku@scylladb.com>
Tests: unit (release)
Message-Id: <f1b985d99f66e5e64d714fd0f087e235b71557d2.1536697368.git.jhaberku@scylladb.com>
This makes the function useable in more contexts due to
flexibility (including in tests), since the state is not captured and
the characteristics of salt generation can be customized to the caller's
needs.
The `generate_salt` function invokes this function internally now.
This change means that `generate_salt` is now thread-safe and therefore
does not have to be invoked by a single thread only when starting the
`password_authenticator`.
This further means that `generate_salt` does not need to be part of the
public interface of the module, and can be moved to the implementation
file.
While the `password_authenticator` is a complex component with lots of
dependencies, password hashing and checking itself is a process with
limited logical state and dependencies, which makes it easy to isolate
and test.
