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use std::convert::TryInto;
use garage_db as db;
use garage_util::data::*;
use garage_util::error::*;
use garage_util::time::*;
use crate::manager::BLOCK_GC_DELAY;
pub struct BlockRc {
pub(crate) rc: db::Tree,
}
impl BlockRc {
pub(crate) fn new(rc: db::Tree) -> Self {
Self { rc }
}
/// Increment the reference counter associated to a hash.
/// Returns true if the RC goes from zero to nonzero.
pub(crate) fn block_incref(&self, tx: &mut db::Transaction, hash: &Hash) -> db::Result<bool> {
let old_rc = RcEntry::parse_opt(tx.get(&self.rc, &hash)?);
match old_rc.increment().serialize() {
Some(x) => {
tx.insert(&self.rc, &hash, x)?;
}
None => unreachable!(),
};
Ok(old_rc.is_zero())
}
/// Decrement the reference counter associated to a hash.
/// Returns true if the RC is now zero.
pub(crate) fn block_decref(&self, tx: &mut db::Transaction, hash: &Hash) -> db::Result<bool> {
let new_rc = RcEntry::parse_opt(tx.get(&self.rc, &hash)?).decrement();
match new_rc.serialize() {
Some(x) => {
tx.insert(&self.rc, &hash, x)?;
}
None => {
tx.remove(&self.rc, &hash)?;
}
};
Ok(matches!(new_rc, RcEntry::Deletable { .. }))
}
/// Read a block's reference count
pub(crate) fn get_block_rc(&self, hash: &Hash) -> Result<RcEntry, Error> {
Ok(RcEntry::parse_opt(self.rc.get(hash.as_ref())?))
}
/// Delete an entry in the RC table if it is deletable and the
/// deletion time has passed
pub(crate) fn clear_deleted_block_rc(&self, hash: &Hash) -> Result<(), Error> {
let now = now_msec();
self.rc.db().transaction(|mut tx| {
let rcval = RcEntry::parse_opt(tx.get(&self.rc, &hash)?);
match rcval {
RcEntry::Deletable { at_time } if now > at_time => {
tx.remove(&self.rc, &hash)?;
}
_ => (),
};
tx.commit(())
})?;
Ok(())
}
}
/// Describes the state of the reference counter for a block
#[derive(Clone, Copy, Debug)]
pub(crate) enum RcEntry {
/// Present: the block has `count` references, with `count` > 0.
///
/// This is stored as u64::to_be_bytes(count)
Present { count: u64 },
/// Deletable: the block has zero references, and can be deleted
/// once time (returned by now_msec) is larger than at_time
/// (in millis since Unix epoch)
///
/// This is stored as [0u8; 8] followed by u64::to_be_bytes(at_time),
/// (this allows for the data format to be backwards compatible with
/// previous Garage versions that didn't have this intermediate state)
Deletable { at_time: u64 },
/// Absent: the block has zero references, and can be deleted
/// immediately
Absent,
}
impl RcEntry {
fn parse(bytes: &[u8]) -> Self {
if bytes.len() == 8 {
RcEntry::Present {
count: u64::from_be_bytes(bytes.try_into().unwrap()),
}
} else if bytes.len() == 16 {
RcEntry::Deletable {
at_time: u64::from_be_bytes(bytes[8..16].try_into().unwrap()),
}
} else {
panic!("Invalid RC entry: {:?}, database is corrupted. This is an error Garage is currently unable to recover from. Sorry, and also please report a bug.",
bytes
)
}
}
fn parse_opt<V: AsRef<[u8]>>(bytes: Option<V>) -> Self {
bytes
.map(|b| Self::parse(b.as_ref()))
.unwrap_or(Self::Absent)
}
fn serialize(self) -> Option<Vec<u8>> {
match self {
RcEntry::Present { count } => Some(u64::to_be_bytes(count).to_vec()),
RcEntry::Deletable { at_time } => {
Some([u64::to_be_bytes(0), u64::to_be_bytes(at_time)].concat())
}
RcEntry::Absent => None,
}
}
fn increment(self) -> Self {
let old_count = match self {
RcEntry::Present { count } => count,
_ => 0,
};
RcEntry::Present {
count: old_count + 1,
}
}
fn decrement(self) -> Self {
match self {
RcEntry::Present { count } => {
if count > 1 {
RcEntry::Present { count: count - 1 }
} else {
RcEntry::Deletable {
at_time: now_msec() + BLOCK_GC_DELAY.as_millis() as u64,
}
}
}
del => del,
}
}
pub(crate) fn is_zero(&self) -> bool {
matches!(self, RcEntry::Deletable { .. } | RcEntry::Absent)
}
pub(crate) fn is_nonzero(&self) -> bool {
!self.is_zero()
}
pub(crate) fn is_deletable(&self) -> bool {
match self {
RcEntry::Present { .. } => false,
RcEntry::Deletable { at_time } => now_msec() > *at_time,
RcEntry::Absent => true,
}
}
pub(crate) fn is_needed(&self) -> bool {
!self.is_deletable()
}
}
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