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Merge pull request #11 from drpcorg/atomic-counters
Atomic counters
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,100 @@ | ||
| package chotki | ||
|
|
||
| import ( | ||
| "context" | ||
| "fmt" | ||
| "sync" | ||
| "sync/atomic" | ||
| "time" | ||
|
|
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| "github.com/drpcorg/chotki/protocol" | ||
| "github.com/drpcorg/chotki/rdx" | ||
| ) | ||
|
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||
| var ErrNotCounter error = fmt.Errorf("not a counter") | ||
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| type AtomicCounter struct { | ||
| db *Chotki | ||
| rid rdx.ID | ||
| offset uint64 | ||
| localValue atomic.Int64 | ||
| tlv atomic.Value | ||
| rdt atomic.Value | ||
| loaded atomic.Bool | ||
| lock sync.Mutex | ||
| expiration time.Time | ||
| updatePeriod time.Duration | ||
| } | ||
|
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||
| // creates counter that has two properties | ||
| // - its atomic as long as you use single instance to do all increments, creating multiple instances will break this guarantee | ||
| // - it can ease CPU load if updatePeiod > 0, in that case it will not read from db backend | ||
| // current value of the counter | ||
| // | ||
| // Because we use LSM backend writes are cheap, reads are expensive. You can trade off up to date value of counter | ||
| // for less CPU cycles | ||
| func NewAtomicCounter(db *Chotki, rid rdx.ID, offset uint64, updatePeriod time.Duration) *AtomicCounter { | ||
| return &AtomicCounter{ | ||
| db: db, | ||
| rid: rid, | ||
| offset: offset, | ||
| updatePeriod: updatePeriod, | ||
| } | ||
| } | ||
|
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| func (a *AtomicCounter) load() error { | ||
| a.lock.Lock() | ||
| defer a.lock.Unlock() | ||
| now := time.Now() | ||
| if a.loaded.Load() && now.Sub(a.expiration) < 0 { | ||
| return nil | ||
| } | ||
| rdt, tlv, err := a.db.ObjectFieldTLV(a.rid.ToOff(a.offset)) | ||
| if err != nil { | ||
| return err | ||
| } | ||
| a.rdt.Store(rdt) | ||
| a.loaded.Store(true) | ||
| a.tlv.Store(tlv) | ||
| switch rdt { | ||
| case rdx.ZCounter: | ||
| a.localValue.Store(rdx.Znative(tlv)) | ||
| case rdx.Natural: | ||
| a.localValue.Store(int64(rdx.Nnative(tlv))) | ||
| default: | ||
| return ErrNotCounter | ||
| } | ||
| a.expiration = now.Add(a.updatePeriod) | ||
| return nil | ||
| } | ||
|
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| // Loads (if needed) and increments counter | ||
| func (a *AtomicCounter) Increment(ctx context.Context, val int64) (int64, error) { | ||
| err := a.load() | ||
| if err != nil { | ||
| return 0, err | ||
| } | ||
| if val == 2 { | ||
| fmt.Println(1) | ||
| } | ||
| rdt := a.rdt.Load().(byte) | ||
| a.localValue.Add(val) | ||
| var dtlv []byte | ||
| a.lock.Lock() | ||
| tlv := a.tlv.Load().([]byte) | ||
| switch rdt { | ||
| case rdx.Natural: | ||
| dtlv = rdx.Ndelta(tlv, uint64(a.localValue.Load()), a.db.Clock()) | ||
| case rdx.ZCounter: | ||
| dtlv = rdx.Zdelta(tlv, a.localValue.Load(), a.db.Clock()) | ||
| default: | ||
| return 0, ErrNotCounter | ||
| } | ||
| a.tlv.Store(dtlv) | ||
| a.lock.Unlock() | ||
| changes := make(protocol.Records, 0) | ||
| changes = append(changes, protocol.Record('F', rdx.ZipUint64(uint64(a.offset)))) | ||
| changes = append(changes, protocol.Record(rdt, dtlv)) | ||
| a.db.CommitPacket(ctx, 'E', a.rid, changes) | ||
| return a.localValue.Load(), nil | ||
| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,119 @@ | ||
| package chotki | ||
|
|
||
| import ( | ||
| "context" | ||
| "os" | ||
| "testing" | ||
| "time" | ||
|
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| "github.com/cockroachdb/pebble" | ||
| "github.com/drpcorg/chotki/protocol" | ||
| "github.com/drpcorg/chotki/rdx" | ||
| "github.com/stretchr/testify/assert" | ||
| ) | ||
|
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| func TestAtomicCounter(t *testing.T) { | ||
| dir, err := os.MkdirTemp("", "*") | ||
| assert.NoError(t, err) | ||
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| a, err := Open(dir, Options{ | ||
| Src: 0x1a, | ||
| Name: "test replica", | ||
| Options: pebble.Options{ErrorIfExists: true}, | ||
| }) | ||
| assert.NoError(t, err) | ||
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| cid, err := a.NewClass(context.Background(), rdx.ID0, Field{Name: "test", RdxType: rdx.Natural}) | ||
| assert.NoError(t, err) | ||
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| rid, err := a.NewObjectTLV(context.Background(), cid, protocol.Records{protocol.Record('N', rdx.Ntlv(0))}) | ||
| assert.NoError(t, err) | ||
|
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| counterA := NewAtomicCounter(a, rid, 1, 0) | ||
| counterB := NewAtomicCounter(a, rid, 1, 0) | ||
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| res, err := counterA.Increment(context.Background(), 1) | ||
| assert.NoError(t, err) | ||
| assert.EqualValues(t, 1, res) | ||
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| res, err = counterB.Increment(context.Background(), 1) | ||
| assert.NoError(t, err) | ||
| assert.EqualValues(t, 2, res) | ||
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| res, err = counterA.Increment(context.Background(), 1) | ||
| assert.NoError(t, err) | ||
| assert.EqualValues(t, 3, res) | ||
| } | ||
|
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| func TestAtomicCounterWithPeriodicUpdate(t *testing.T) { | ||
| dira, err := os.MkdirTemp("", "*") | ||
| assert.NoError(t, err) | ||
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| a, err := Open(dira, Options{ | ||
| Src: 0x1a, | ||
| Name: "test replica", | ||
| Options: pebble.Options{ErrorIfExists: true}, | ||
| }) | ||
| assert.NoError(t, err) | ||
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| dirb, err := os.MkdirTemp("", "*") | ||
| assert.NoError(t, err) | ||
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| b, err := Open(dirb, Options{ | ||
| Src: 0x1b, | ||
| Name: "test replica2", | ||
| Options: pebble.Options{ErrorIfExists: true}, | ||
| }) | ||
| assert.NoError(t, err) | ||
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| cid, err := a.NewClass( | ||
| context.Background(), rdx.ID0, | ||
| Field{Name: "test", RdxType: rdx.Natural}, | ||
| Field{Name: "test2", RdxType: rdx.ZCounter}, | ||
| ) | ||
| assert.NoError(t, err) | ||
|
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| rid, err := a.NewObjectTLV( | ||
| context.Background(), cid, | ||
| protocol.Records{ | ||
| protocol.Record('N', rdx.Ntlv(0)), | ||
| protocol.Record('Z', rdx.Ztlv(0)), | ||
| }, | ||
| ) | ||
| assert.NoError(t, err) | ||
|
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| ctx, cancel := context.WithCancel(context.Background()) | ||
| defer cancel() | ||
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| for i := 1; i <= 2; i++ { | ||
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| counterA := NewAtomicCounter(a, rid, uint64(i), 100*time.Millisecond) | ||
| counterB := NewAtomicCounter(b, rid, uint64(i), 0) | ||
|
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| // first increment | ||
| res, err := counterA.Increment(ctx, 1) | ||
| assert.NoError(t, err) | ||
| assert.EqualValues(t, 1, res) | ||
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| syncData(a, b) | ||
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| // increment from another replica | ||
| res, err = counterB.Increment(ctx, 1) | ||
| assert.NoError(t, err) | ||
| assert.EqualValues(t, 2, res) | ||
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| syncData(a, b) | ||
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| // this increment does not account data from other replica because current value is cached | ||
| res, err = counterA.Increment(ctx, 1) | ||
| assert.NoError(t, err) | ||
| assert.EqualValues(t, 2, res) | ||
|
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| time.Sleep(100 * time.Millisecond) | ||
|
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| // after wait we increment, and we get actual value | ||
| res, err = counterA.Increment(ctx, 1) | ||
| assert.NoError(t, err) | ||
| assert.EqualValues(t, 4, res) | ||
| } | ||
| } |
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