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use std::{
error::Error as StdError,
fmt::{self, Display},
};
use super::*;
/// A transaction-related Result
pub type TxResult<A> = std::result::Result<A, TxError>;
/// A transaction-related error
#[derive(Debug, Clone)]
pub enum TxError {
/// An error in the underlying IO and Caching system
PageCache(Error),
/// An intentionally-aborted transaction
Abort,
/// Another transaction interfered with this one
Conflict,
}
impl From<Error> for TxError {
fn from(error: Error) -> TxError {
TxError::PageCache(error)
}
}
impl Display for TxError {
fn fmt(
&self,
f: &mut fmt::Formatter<'_>,
) -> std::result::Result<(), fmt::Error> {
match *self {
TxError::PageCache(ref error) => <Error as Display>::fmt(&error, f),
TxError::Abort => write!(f, "transaction was aborted"),
TxError::Conflict => write!(
f,
"transaction encountered a \
conflicting concurrent transaction"
),
}
}
}
impl StdError for TxError {
fn description(&self) -> &str {
match *self {
TxError::PageCache(ref error) => error.description(),
TxError::Abort => "transaction was aborted",
TxError::Conflict => {
"transaction encountered a \
conflicting concurrent transaction"
}
}
}
}
/// A handle to an ongoing pagecache transaction. Ensures
/// that any state which is removed from a shared in-memory
/// data structure is not destroyed until all possible
/// readers have concluded.
pub struct Tx<P>
where
P: DeserializeOwned + Serialize,
{
#[doc(hidden)]
pub guard: Guard,
#[doc(hidden)]
pub ts: u64,
pub(crate) pending: FastMap8<PageId, Update<P>>,
}
impl<P> Tx<P>
where
P: DeserializeOwned + Serialize + Send + Sync,
{
/// Creates a new Tx with a given timestamp.
pub fn new(ts: u64) -> Self {
Self {
guard: pin(),
ts,
pending: FastMap8::default(),
}
}
/// Atomically commit this transaction by
/// checking all read and written pages for
/// conflicts, and then writing changes in a
/// way that cannot be partially recovered
/// (will either be 100% recovered or 100%
/// aborted in the case of a conflict or
/// crash that happens before the entire
/// write set can be persisted to disk).
///
/// This is optimistic, which gets better
/// performance with many threads that write
/// to separate pages, but may abort
/// if threads are writing to the same pages.
pub fn commit(self) -> TxResult<()> {
unimplemented!()
}
/// Create a new page, trying to reuse old freed pages if possible
/// to maximize underlying `PageTable` pointer density. Returns
/// the page ID and its pointer for use in future `replace`
/// and `link` operations.
pub fn allocate<'g>(
&'g self,
new: P,
) -> TxResult<(PageId, PagePtr<'g, P>)> {
unimplemented!()
}
/// Free a particular page.
pub fn free<'g>(
&'g self,
pid: PageId,
old: PagePtr<'g, P>,
) -> TxResult<CasResult<'g, P, ()>> {
unimplemented!()
}
/// Try to atomically add a `PageFrag` to the page.
/// Returns `Ok(new_key)` if the operation was successful. Returns
/// `Err(None)` if the page no longer exists. Returns `Err(Some(actual_key))`
/// if the atomic append fails.
pub fn link<'g>(
&'g self,
pid: PageId,
old: PagePtr<'g, P>,
new: P,
) -> TxResult<CasResult<'g, P, P>> {
unimplemented!()
}
/// Replace an existing page with a different set of `PageFrag`s.
/// Returns `Ok(new_key)` if the operation was successful. Returns
/// `Err(None)` if the page no longer exists. Returns `Err(Some(actual_key))`
/// if the atomic swap fails.
pub fn replace<'g>(
&'g self,
pid: PageId,
old: PagePtr<'g, P>,
new: P,
) -> TxResult<CasResult<'g, P, P>> {
unimplemented!()
}
/// Try to retrieve a page by its logical ID.
pub fn get<'g>(
&'g self,
pid: PageId,
) -> TxResult<(PagePtr<'g, P>, Vec<&'g P>)> {
unimplemented!()
}
}
impl<P> std::ops::Deref for Tx<P>
where
P: DeserializeOwned + Serialize,
{
type Target = Guard;
fn deref(&self) -> &Guard {
&self.guard
}
}