Remove the Flush method from Exemplar (#4873)

Co-authored-by: Robert Pająk <pellared@hotmail.com>

sdk/metric/internal/exemplar/drop.go

@@ -34,8 +34,3 @@ func (r *dropRes[N]) Offer(context.Context, time.Time, N, []attribute.KeyValue)
 func (r *dropRes[N]) Collect(dest *[]metricdata.Exemplar[N]) {
 	*dest = (*dest)[:0]
 }
-
-// Flush resets dest. No exemplars will ever be returned.
-func (r *dropRes[N]) Flush(dest *[]metricdata.Exemplar[N]) {
-	*dest = (*dest)[:0]
-}

sdk/metric/internal/exemplar/filter_test.go

@@ -44,9 +44,6 @@ func testSampledFiltered[N int64 | float64](t *testing.T) {
 
 	r.Collect(nil)
 	assert.True(t, under.CollectCalled, "underlying Reservoir Collect not called")
-
-	r.Flush(nil)
-	assert.True(t, under.FlushCalled, "underlying Reservoir Flush not called")
 }
 
 func sample(parent context.Context) context.Context {
@@ -61,7 +58,6 @@ func sample(parent context.Context) context.Context {
 type res[N int64 | float64] struct {
 	OfferCalled   bool
 	CollectCalled bool
-	FlushCalled   bool
 }
 
 func (r *res[N]) Offer(context.Context, time.Time, N, []attribute.KeyValue) {
@@ -71,7 +67,3 @@ func (r *res[N]) Offer(context.Context, time.Time, N, []attribute.KeyValue) {
 func (r *res[N]) Collect(*[]metricdata.Exemplar[N]) {
 	r.CollectCalled = true
 }
-
-func (r *res[N]) Flush(*[]metricdata.Exemplar[N]) {
-	r.FlushCalled = true
-}

sdk/metric/internal/exemplar/rand.go

@@ -193,8 +193,3 @@ func (r *randRes[N]) Collect(dest *[]metricdata.Exemplar[N]) {
 	// measurements that are made over the older collection cycle ones.
 	r.reset()
 }
-
-func (r *randRes[N]) Flush(dest *[]metricdata.Exemplar[N]) {
-	r.storage.Flush(dest)
-	r.reset()
-}

sdk/metric/internal/exemplar/reservoir.go

@@ -39,13 +39,6 @@ type Reservoir[N int64 | float64] interface {
 
 	// Collect returns all the held exemplars.
 	//
-	// The Reservoir state is preserved after this call. See Flush to
-	// copy-and-clear instead.
+	// The Reservoir state is preserved after this call.
 	Collect(dest *[]metricdata.Exemplar[N])
-
-	// Flush returns all the held exemplars.
-	//
-	// The Reservoir state is reset after this call. See Collect to preserve
-	// the state instead.
-	Flush(dest *[]metricdata.Exemplar[N])
 }

sdk/metric/internal/exemplar/reservoir_test.go

@@ -92,25 +92,6 @@ func ReservoirTest[N int64 | float64](f factory[N]) func(*testing.T) {
 			assert.Equal(t, want, dest[0])
 		})
 
-		t.Run("CollectDoesNotFlush", func(t *testing.T) {
-			t.Helper()
-
-			r, n := f(1)
-			if n < 1 {
-				t.Skip("skipping, reservoir capacity less than 1:", n)
-			}
-
-			r.Offer(ctx, staticTime, 10, nil)
-
-			var dest []metricdata.Exemplar[N]
-			r.Collect(&dest)
-			require.Len(t, dest, 1, "number of collected exemplars")
-
-			dest = dest[:0]
-			r.Collect(&dest)
-			assert.Len(t, dest, 1, "Collect flushed reservoir")
-		})
-
 		t.Run("CollectLessThanN", func(t *testing.T) {
 			t.Helper()
 
@@ -127,24 +108,6 @@ func ReservoirTest[N int64 | float64](f factory[N]) func(*testing.T) {
 			require.Len(t, dest, 1, "number of collected exemplars")
 		})
 
-		t.Run("FlushFlushes", func(t *testing.T) {
-			t.Helper()
-
-			r, n := f(1)
-			if n < 1 {
-				t.Skip("skipping, reservoir capacity less than 1:", n)
-			}
-
-			r.Offer(ctx, staticTime, 10, nil)
-
-			var dest []metricdata.Exemplar[N]
-			r.Flush(&dest)
-			require.Len(t, dest, 1, "number of flushed exemplars")
-
-			r.Flush(&dest)
-			assert.Len(t, dest, 0, "Flush did not flush reservoir")
-		})
-
 		t.Run("MultipleOffers", func(t *testing.T) {
 			t.Helper()
 
@@ -159,17 +122,17 @@ func ReservoirTest[N int64 | float64](f factory[N]) func(*testing.T) {
 			}
 
 			var dest []metricdata.Exemplar[N]
-			r.Flush(&dest)
+			r.Collect(&dest)
 			assert.Len(t, dest, n, "multiple offers did not fill reservoir")
 
-			// Ensure the flush reset also resets any couting state.
+			// Ensure the collect reset also resets any couting state.
 			for i := 0; i < n+1; i++ {
-				v := N(2 * i)
+				v := N(i)
 				r.Offer(ctx, staticTime, v, nil)
 			}
 
 			dest = dest[:0]
-			r.Flush(&dest)
+			r.Collect(&dest)
 			assert.Len(t, dest, n, "internal count state not reset")
 		})
 
@@ -186,11 +149,6 @@ func ReservoirTest[N int64 | float64](f factory[N]) func(*testing.T) {
 			dest := []metricdata.Exemplar[N]{{}} // Should be reset to empty.
 			r.Collect(&dest)
 			assert.Len(t, dest, 0, "no exemplars should be collected")
-
-			r.Offer(context.Background(), staticTime, 10, nil)
-			dest = []metricdata.Exemplar[N]{{}} // Should be reset to empty.
-			r.Flush(&dest)
-			assert.Len(t, dest, 0, "no exemplars should be flushed")
 		})
 	}
 }

sdk/metric/internal/exemplar/storage.go

@@ -38,8 +38,7 @@ func newStorage[N int64 | float64](n int) *storage[N] {
 
 // Collect returns all the held exemplars.
 //
-// The Reservoir state is preserved after this call. See Flush to
-// copy-and-clear instead.
+// The Reservoir state is preserved after this call.
 func (r *storage[N]) Collect(dest *[]metricdata.Exemplar[N]) {
 	*dest = reset(*dest, len(r.store), len(r.store))
 	var n int
@@ -54,27 +53,6 @@ func (r *storage[N]) Collect(dest *[]metricdata.Exemplar[N]) {
 	*dest = (*dest)[:n]
 }
 
-// Flush returns all the held exemplars.
-//
-// The Reservoir state is reset after this call. See Collect to preserve the
-// state instead.
-func (r *storage[N]) Flush(dest *[]metricdata.Exemplar[N]) {
-	*dest = reset(*dest, len(r.store), len(r.store))
-	var n int
-	for i, m := range r.store {
-		if !m.valid {
-			continue
-		}
-
-		m.Exemplar(&(*dest)[n])
-		n++
-
-		// Reset.
-		r.store[i] = measurement[N]{}
-	}
-	*dest = (*dest)[:n]
-}
-
 // measurement is a measurement made by a telemetry system.
 type measurement[N int64 | float64] struct {
 	// FilteredAttributes are the attributes dropped during the measurement.