Struct mz_coord::coord::timeline::TimestampOracle

pub struct TimestampOracle<T> {
    state: TimestampOracleState<T>,
    advance_to: Option<T>,
    next: Box<dyn Fn() -> T>,
}

A type that provides write and read timestamps, reads observe exactly their preceding writes..

Specifically, all read timestamps will be greater or equal to all previously reported write timestamps, and strictly less than all subsequently emitted write timestamps.

Fields

state: TimestampOracleState<T>

advance_to: Option<T>

next: Box<dyn Fn() -> T>

Implementations

impl<T: CoordTimestamp> TimestampOracle<T>

pub fn new<F>(initially: T, next: F) -> Self where
    F: Fn() -> T + 'static, 

Create a new timeline, starting at the indicated time. next generates new timestamps when invoked. The timestamps have no requirements, and can retreat from previous invocations.

pub fn peek_ts(&self) -> T

Peek the current value of the timestamp.

No operations should be assigned to the timestamp returned by this function. The timestamp returned should only be used to compare the progress of the TimestampOracle against some external source of time.

Subsequent values of self.read_ts() and self.write_ts() will be greater or equal to this timestamp.

NOTE: This can be removed once DDL is included in group commits.

pub fn write_ts(&mut self) -> T

Acquire a new timestamp for writing.

This timestamp will be strictly greater than all prior values of self.read_ts(), and less than or equal to all subsequent values of self.read_ts().

pub fn read_ts(&mut self) -> T

Acquire a new timestamp for reading.

This timestamp will be greater or equal to all prior values of self.write_ts(), and strictly less than all subsequent values of self.write_ts().

pub fn fast_forward(&mut self, lower_bound: T)

Electively advance the tracked times.

If lower_bound is strictly greater than the current time (of either state), the resulting state will be Writing(lower_bound).

pub fn should_advance_to(&mut self) -> Option<T>

Whether and to what the next value of `self.write_ts() has advanced since this method was last called.

This method may produce the same value multiple times, and should not be used as a test for whether a write-to-read transition has occurred, so much as an advisory signal that write capabilities can advance.