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use std::sync::Arc;
use parking_lot::Mutex;
use super::*;
#[derive(Clone)]
pub(crate) struct Context {
// TODO file from config should be in here
config: Config,
/// Periodically flushes dirty data. We keep this in an
/// Arc separate from the PageCache below to separate
/// "high-level" references from Db, Tree etc... from
/// "low-level" references like background threads.
/// When the last high-level reference is dropped, it
/// should trigger all background threads to clean
/// up synchronously.
pub(crate) _flusher: Arc<Mutex<Option<flusher::Flusher>>>,
pub(crate) pagecache: Arc<PageCache<Frag>>,
}
impl std::ops::Deref for Context {
type Target = Config;
fn deref(&self) -> &Config {
&self.config
}
}
impl Drop for Context {
fn drop(&mut self) {
loop {
match self.pagecache.flush() {
Ok(0) => return,
Ok(_) => continue,
Err(e) => {
error!(
"failed to flush underlying \
pagecache during drop: {:?}",
e
);
return;
}
}
}
}
}
impl Context {
pub(crate) fn start(config: Config) -> Result<Self> {
trace!("starting context");
#[cfg(any(test, feature = "check_snapshot_integrity"))]
match config.verify_snapshot() {
#[cfg(not(feature = "failpoints"))]
Ok(_) => {}
#[cfg(feature = "failpoints")]
Ok(_) | Err(Error::FailPoint) => {}
other => panic!("failed to verify snapshot: {:?}", other),
}
let pagecache = Arc::new(PageCache::start(config.clone())?);
Ok(Self {
config,
pagecache,
_flusher: Arc::new(Mutex::new(None)),
})
}
/// Returns `true` if the database was
/// recovered from a previous process.
/// Note that database state is only
/// guaranteed to be present up to the
/// last call to `flush`! Otherwise state
/// is synced to disk periodically if the
/// `sync_every_ms` configuration option
/// is set to `Some(number_of_ms_between_syncs)`
/// or if the IO buffer gets filled to
/// capacity before being rotated.
pub fn was_recovered(&self) -> bool {
self.pagecache.was_recovered()
}
/// Generate a monotonic ID. Not guaranteed to be
/// contiguous. Written to disk every `idgen_persist_interval`
/// operations, followed by a blocking flush. During recovery, we
/// take the last recovered generated ID and add 2x
/// the `idgen_persist_interval` to it. While persisting, if the
/// previous persisted counter wasn't synced to disk yet, we will do
/// a blocking flush to fsync the latest counter, ensuring
/// that we will never give out the same counter twice.
pub fn generate_id(&self) -> Result<u64> {
self.pagecache.generate_id()
}
pub(crate) fn pin_log(&self) -> Result<RecoveryGuard> {
self.pagecache.pin_log()
}
}