pdf of design

render-2023-10-11/cmd/cache-service/oplog.go

@@ -1,12 +1,15 @@
 package main
 
 import (
+	"fmt"
 	"render231011/internal/thestore"
 	"slices"
+	"sync"
 	"time"
 )
 
 type Oplog struct {
+	mutex         *sync.RWMutex
 	events        []timestampedEvent
 	idx           int // todo
 	lastTruncated time.Time
@@ -17,10 +20,15 @@ type timestampedEvent struct {
 	e thestore.Event
 }
 
+func (timestampedEvent timestampedEvent) String() string {
+	return fmt.Sprintf("@%v: %+v", timestampedEvent.t.Unix(), timestampedEvent.e)
+}
+
 // gotcha duration? bigger N? whatever
 func NewOplog() *Oplog {
 	return &Oplog{
-		events: make([]timestampedEvent, 0, 1024),
+		events: make([]timestampedEvent, 2),
+		mutex:  &sync.RWMutex{},
 	}
 }
 
@@ -30,23 +38,39 @@ func (oplog *Oplog) Push(event thestore.Event) {
 }
 
 func (oplog *Oplog) push(t time.Time, event thestore.Event) {
-	oplog.events = append(oplog.events, timestampedEvent{
+	oplog.mutex.Lock()
+	defer oplog.mutex.Unlock()
+	oplog.lastTruncated = oplog.events[oplog.idx].t
+	oplog.events[oplog.idx] = timestampedEvent{
 		t: t,
 		e: event,
-	})
+	}
+	oplog.idx++
+	if oplog.idx >= len(oplog.events) {
+		oplog.idx = 0
+	}
 }
 
 func (oplog *Oplog) Since(t time.Time) ([]thestore.Event, bool) {
+	oplog.mutex.RLock()
+	defer oplog.mutex.RUnlock()
+
 	if !t.After(oplog.lastTruncated) {
 		return nil, false
 	}
 
 	result := make([]thestore.Event, 0, 5)
-	for i := len(oplog.events) - 1; i >= 0; i-- {
+	i := (oplog.idx + len(oplog.events) - 1) % len(oplog.events)
+	for i != oplog.idx {
 		if !oplog.events[i].t.After(t) {
 			break
 		}
 		result = append(result, oplog.events[i].e)
+
+		i--
+		if i < 0 {
+			i = len(oplog.events)
+		}
 	}
 	slices.Reverse(result)
 	return result, len(result) > 0

render-2023-10-11/cmd/cache-service/oplog_test.go

@@ -13,6 +13,8 @@ func TestOplog(t *testing.T) {
 	oplog.push(time.Unix(3, 0), thestore.Event{ID: "3"})
 	oplog.push(time.Unix(4, 0), thestore.Event{ID: "4"})
 
+	t.Logf("%+v, %s", oplog, oplog.lastTruncated.UTC())
+
 	got, _ := oplog.Since(time.Unix(2, 0))
 	if len(got) != 2 {
 		t.Error(got)