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>
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