Replace the per-shard value we store with an updateable_value_source, which
allows updating it dynamically and allows users to track changes.
The broadcast_to_all_shards() function is augmented to apply modifications
when called on a live system.
Currently, we allow adjusting configuration via
cfg.whatever() = 5;
by returning a mutable reference from cfg.whatever(). Soon, however, this operation
will have side effects (updating all references to the config item, and triggering
notifiers). While this can be done with a proxy, it is too tricky.
Switch to an ordinary setter interface:
cfg.whatever.set(5);
Because boost::program_options no longer gets a reference to the value to be written
to, we have to move the update to a notifier, and the value_ex() function has to
be adjusted to infer whether it was called with a vector type after it is
called, not before.
Currently, the REST API does its own conversion of named_value into json.
This requires it to use the _make_config_values macro to perform iteration
of all config items, since it needs to preserve the concrete type of the item
while iterating, so it can select the correct json conversion.
Since we want to remove that macro, we need to provide a different way to
convert a config item to json. So this patch adds a value_as_json().
To hide json_return_value from the rest of the system, we extend config_type
with a conversion function to handle the details. This usually calls
the json_return_type constructor directly, but when it doesn't have default
translation, it interposes a conversion into a type that json recognizes.
I didn't bother maintaining the existing type names, since they're C++
names which don't make sense for the UI.
The value_status is only needed at run-time, and removing it from the
template parameter list reduces type proliferation (which leads to code
bloat) and simplifies the code.
Replace stdx::optional and stdx::string_view with the C++ std
counterparts.
Some instances of boost::variant were also replaced with std::variant,
namely those that called seastar::visit.
Scylla now requires GCC 8 to compile.
Signed-off-by: Duarte Nunes <duarte@scylladb.com>
Message-Id: <20190108111141.5369-1-duarte@scylladb.com>
Handling all the boost::commandline + YAML stuff.
This patch only provides an external version of these functions,
it does not modify the db::config object. That is for a follow-up
patch.
