[Consensus] use system time for clock

consensus/core/src/context.rs

@@ -1,7 +1,7 @@
 // Copyright (c) Mysten Labs, Inc.
 // SPDX-License-Identifier: Apache-2.0
 
-use std::{sync::Arc, time::SystemTime};
+use std::{sync::{atomic::{AtomicU64, Ordering}, Arc}, time::SystemTime};
 
 use consensus_config::{AuthorityIndex, Committee, Parameters};
 #[cfg(test)]
@@ -102,28 +102,20 @@ impl Context {
 /// wherever is needed in order to make sure that consecutive calls to receive the system timestamp
 /// will remain monotonically increasing.
 pub(crate) struct Clock {
- unix_epoch_instant: Instant,
+ last_ts: AtomicU64,
 }
 
 impl Clock {
  pub fn new() -> Self {
- let now = Instant::now();
- let duration_since_unix_epoch =
- match SystemTime::now().duration_since(SystemTime::UNIX_EPOCH) {
- Ok(d) => d,
- Err(e) => panic!("SystemTime before UNIX EPOCH! {e}"),
- };
- let unix_epoch_instant = now.checked_sub(duration_since_unix_epoch).unwrap();
-
- Self { unix_epoch_instant }
+ let last_ts = SystemTime::now().duration_since(SystemTime::UNIX_EPOCH).unwrap().as_millis() as u64;
+ Self { last_ts: AtomicU64::new(last_ts) }
  }
 
  // Returns the current time expressed as UNIX timestamp in milliseconds.
- // Calculated with Rust Instant to ensure monotonicity.
+ // Ensure monotonicity even if system time goes back.
  pub(crate) fn timestamp_utc_ms(&self) -> BlockTimestampMs {
- Instant::now()
- .checked_duration_since(self.unix_epoch_instant)
- .unwrap()
- .as_millis() as BlockTimestampMs
+ let now_ts = SystemTime::now().duration_since(SystemTime::UNIX_EPOCH).unwrap().as_millis() as u64;
+ let prev_ts = self.last_ts.fetch_max(now_ts, Ordering::SeqCst);
+ now_ts.max(prev_ts)
  }
 }