david
d6d2a24ddc
Applies gofmt to the 18 files that were already unformatted at HEAD (pre-existing debt — 122 insertions / 122 deletions, whitespace plus import-block reorderings only; `git diff -w` confirms no semantic changes). Kept on its own branch so the functional change set (see the review-hardening PR) stays reviewable without formatting noise. Verified: go build, go vet, go test ./... pass on this branch; a merge simulation with the functional branch produces a clean 3-way merge with all tests green. Reviewed-on: #4 Co-authored-by: David Gwilliam <dhgwilliam@gmail.com> Co-committed-by: David Gwilliam <dhgwilliam@gmail.com>
61 lines
1.9 KiB
Go
61 lines
1.9 KiB
Go
// Package hlc implements a Hybrid Logical Clock for ordering observations.
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//
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// A node's HLC is monotonic even when wall clocks jump (NTP correction, suspend).
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// Values are packed into an int64: high bits = wall-clock milliseconds, low bits
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// = per-millisecond sequence. Lexicographic comparison of the packed value is a
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// causal order (states: causally-related events have distinct values; concurrent
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// events never collide because the sequence bumps on any wall-clock stall).
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package hlc
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import (
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"sync"
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"time"
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)
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// seqBits is the number of low bits reserved for the per-millisecond sequence,
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// giving 2^22 ≈ 4.2M slots per ms — far beyond ingest rates.
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const seqBits = 22
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const seqMask = int64(1)<<seqBits - 1
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const wallShift = seqBits
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// Clock is a single-writer HLC. It is safe for concurrent use.
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type Clock struct {
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mu sync.Mutex
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wallMS int64 // last observed wall-clock millis
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seq int64 // sequence within the current wallMillis bucket
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}
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func New() *Clock { return &Clock{} }
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// Now returns the next monotonic HLC value and the wall-clock time embedded in
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// it. The returned time is the HLC's wall component — never ahead of the local
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// clock beyond the current call and never rewinding across calls.
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func (c *Clock) Now() (int64, time.Time) {
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c.mu.Lock()
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defer c.mu.Unlock()
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w := time.Now().UnixMilli()
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if w > c.wallMS {
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c.wallMS = w
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c.seq = 0
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} else {
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// Wall clock stalled or went backwards (NTP): keep wallMS but bump seq
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// so the value is still strictly increasing.
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if c.seq >= seqMask {
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// Extremely unlikely (4.2M events in one ms); jump the wall lazily.
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c.wallMS++
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c.seq = 0
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} else {
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c.seq++
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}
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}
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v := c.wallMS<<wallShift | c.seq
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return v, time.UnixMilli(c.wallMS).UTC()
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}
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// WallTime extracts the wall-clock component embedded in a packed HLC value.
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func WallTime(v int64) time.Time {
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return time.UnixMilli(v >> wallShift).UTC()
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}
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