diff options
Diffstat (limited to 'util/lamport/mem_clock.go')
| -rw-r--r-- | util/lamport/mem_clock.go | 14 |
1 files changed, 11 insertions, 3 deletions
diff --git a/util/lamport/mem_clock.go b/util/lamport/mem_clock.go index ce6f2d4d..d824d834 100644 --- a/util/lamport/mem_clock.go +++ b/util/lamport/mem_clock.go @@ -25,6 +25,14 @@ */ +// Note: this code originally originate from Hashicorp's Serf but has been changed since to fit git-bug's need. + +// Note: this Lamport clock implementation is different than the algorithms you can find, notably Wikipedia or the +// original Serf implementation. The reason is lie to what constitute an event in this distributed system. +// Commonly, events happen when messages are sent or received, whereas in git-bug events happen when some data is +// written, but *not* when read. This is why Witness set the time to the max seen value instead of max seen value +1. +// See https://cs.stackexchange.com/a/133730/129795 + package lamport import ( @@ -62,7 +70,7 @@ func (mc *MemClock) Time() Time { // Increment is used to return the value of the lamport clock and increment it afterwards func (mc *MemClock) Increment() (Time, error) { - return Time(atomic.AddUint64(&mc.counter, 1) - 1), nil + return Time(atomic.AddUint64(&mc.counter, 1)), nil } // Witness is called to update our local clock if necessary after @@ -72,12 +80,12 @@ WITNESS: // If the other value is old, we do not need to do anything cur := atomic.LoadUint64(&mc.counter) other := uint64(v) - if other < cur { + if other <= cur { return nil } // Ensure that our local clock is at least one ahead. - if !atomic.CompareAndSwapUint64(&mc.counter, cur, other+1) { + if !atomic.CompareAndSwapUint64(&mc.counter, cur, other) { // CAS: CompareAndSwap // The CAS failed, so we just retry. Eventually our CAS should // succeed or a future witness will pass us by and our witness |