matrei commented on issue #15840:
URL: https://github.com/apache/grails-core/issues/15840#issuecomment-6031663768
@weinellucian I could reproduce the empty restore on 7.1.0 with a single app
as soon as `spring.profiles.active` is set as a JVM system property: the backup
created with `new PropertySourcesConfig(configMap)` is already empty, and after
`clear()`/`merge()` the config is `[:]`. Since system properties are shared by
all apps in the same Tomcat, that is likely what triggers it in your setup.
#16547 should fix this regression. But I'd also recommend moving away from
clearing and re-merging `Holders.config` at runtime:
- `clear()` followed by `merge()` is not atomic. The config is backed by a
plain `LinkedHashMap`, so while the job runs, request threads can see an empty
or half-merged config.
- Many values are copied out of the config once at startup (`@Value`,
`@ConfigurationProperties`, `GrailsConfigurationAware`, plugin bean
definitions, datasource settings). Those won't pick up reloaded values anyway,
so only code that calls `config.getProperty(...)` on every use sees the changes.
- It relies on internal merge semantics, which is how this broke between 6
and 7.
A small settings service addresses these. Keep the database values in an
immutable snapshot, swap it in a single assignment, and fall back to the static
config for anything not stored in the database:
```groovy
import grails.core.GrailsApplication
import grails.gorm.transactions.Transactional
class SettingsService {
GrailsApplication grailsApplication
private volatile Map<String, String> settings = Collections.emptyMap()
String getSetting(String key) {
settings.containsKey(key) ? settings[key] :
grailsApplication.config.getProperty(key)
}
@Transactional(readOnly = true)
void reload() {
var loaded = [:] as Map<String, String>
AppSetting.list().each { loaded[it.name] = it.settingValue }
settings = Collections.unmodifiableMap(loaded)
}
}
```
Call `settingsService.reload()` from `BootStrap` and from your cron job, and
read dynamic values through `settingsService.getSetting(...)` instead of
`Holders.config`. Readers always see either the old snapshot or the new one,
never an empty config, and `application.yml`/external config stay untouched, so
there is nothing to back up and restore.
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