If the object returned from observe() is destructured,
it stops observing, potentially causing subtle bugs.
Typically, the observer object is retained as a class member.
Fixes some typos as found by codespell run on the code.
In this commit, I was hoping to fix only comments, not user-visible alerts, output, etc.
Follow-up commits will take care of them.
Refs: https://github.com/scylladb/scylladb/issues/16255
Signed-off-by: Yaniv Kaul <yaniv.kaul@scylladb.com>
Automatically updates a value from a utils::updateable_value
Where they can be of different types.
An optional transfom function can provide an additional transformation
when updating the value, like multiplying it by a factor for unit conversion,
for example.
To be used for auto-updating the large data thresholds
from the db::config.
Signed-off-by: Benny Halevy <bhalevy@scylladb.com>
An updateable_value() may come without source attached. One of the
options how this can happen is if the value sits on a service config.
It's a good option to make the config have some default initialization
for the option, but in this case observe()ing an option by the service
would step on null pointer dereference.
Said that, if a value without source is tried to be observed -- assume
that it's OK, but the value would never change, so a dummy observer is
to be provided.
Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>
Instead of lengthy blurbs, switch to single-line, machine-readable
standardized (https://spdx.dev) license identifiers. The Linux kernel
switched long ago, so there is strong precedent.
Three cases are handled: AGPL-only, Apache-only, and dual licensed.
For the latter case, I chose (AGPL-3.0-or-later and Apache-2.0),
reasoning that our changes are extensive enough to apply our license.
The changes we applied mechanically with a script, except to
licenses/README.md.
Closes#9937
The updateable_value and updateable_value_source classes allow broadcasting
configuration changes across the application. The updateable_value_source class
represents a value that can be updated, and updateable_value tracks its source
and reflects changes. A typical use replaces "uint64_t config_item" with
"updateable_value<uint64_t> config_item", and from now on changes to the source
will be reflected in config_item. For more complicated uses, which must run some
callback when configuration changes, you can also call
config_item.observe(callback) to be actively notified of changes.
