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PBTS: changes in arXiv algorithm made more clear

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Daniel Cason
2022-05-24 18:28:31 +02:00
committed by Daniel
parent e6d1f7d96e
commit 798bd3c4c6
1 changed files with 10 additions and 14 deletions
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spec/consensus/proposer-based-timestamp/pbts-algorithm_002_draft.md
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@@ -65,15 +65,13 @@ the clock of `p` is `PRECISION` *ahead* of the clock of the proposer of `v`, and
The following changes are proposed for the algorithm in the [arXiv paper][arXiv].
#### New `StartRound`
#### New `StartRound` (Lines 11 - 21)
There are two additions to the `propose` round step when executed by the `proposer` of a round:
1. to ensure time monotonicity, the proposer does not propose a value until its current local time becomes greater than the previously decided value's time
1. when the proposer produce a new proposal it sets the proposal's time to its current local time
- no changes are made to the logic when a proposer has a non-nil `validValue`, which retains its original proposal time.
#### **[PBTS-ALG-STARTROUND.1]**
1. The proposer does not propose a value until its current local time becomes greater than the previously decided value's time;
1. When the proposer produces a new proposal, it sets the proposal's time to its current local time;
- No changes are made to the logic when a proposer re-proposes its `validValue`, which retains its original proposal time.
```go
function StartRound(round) {
@@ -94,20 +92,18 @@ function StartRound(round) {
}
```
#### New Rule Replacing Lines 22 - 27
#### New rule for accepting values (Lines 22 - 27)
The rule on line 22 applies to values `v` proposed for the first time, i.e., for proposals not backed by `2f + 1 PREVOTE`s for `v` in a previous round.
The rule on line 22 applies to values `v` proposed for the first time, i.e., for proposals not backed by `PREVOTE`s for `v` in a previous round `vr < r`.
The `PROPOSAL` message, in this case, carry `-1` in its `validRound` field.
The new rule for issuing a `PREVOTE` for a proposed value `v` requires the value to be `timely`.
As the `timely` predicate is evaluated in the moment that the value is received,
as part of a `PROPOSAL` message, we require the `PROPOSAL` message to be `timely`.
#### **[PBTS-ALG-UPON-PROP.1]**
The `timely` predicate is evaluated in the moment that the value is received,
as part of a `PROPOSAL` message, by comparing the process local time with `v.time`.
```go
upon timely(⟨PROPOSAL, h_p, round_p, v, −1⟩) from proposer(h_p, round_p) while step_p = propose do {
if valid(v) ∧ (lockedRound_p = −1 ∨ lockedValue_p = v) {
upon ⟨PROPOSAL, h_p, round_p, v, −1⟩ from proposer(h_p, round_p) while step_p = propose do {
if timely(v.time) ∧ valid(v) ∧ (lockedRound_p = −1 ∨ lockedValue_p = v) {
broadcast ⟨PREVOTE, h_p, round_p, id(v)⟩
}
else {