[GitHub] [yunikorn-core] craigcondit commented on a diff in pull request #562: [YUNIKORN-1799] Create basic ringbuffer implementation

["craigcondit (via GitHub)" <gi...@apache.org>]

craigcondit commented on code in PR #562:
URL: https://github.com/apache/yunikorn-core/pull/562#discussion_r1227076850


##########
pkg/events/event_ringbuffer.go:
##########
@@ -0,0 +1,167 @@
+/*
+ Licensed to the Apache Software Foundation (ASF) under one
+ or more contributor license agreements.  See the NOTICE file
+ distributed with this work for additional information
+ regarding copyright ownership.  The ASF licenses this file
+ to you under the Apache License, Version 2.0 (the
+ "License"); you may not use this file except in compliance
+ with the License.  You may obtain a copy of the License at
+
+     http://www.apache.org/licenses/LICENSE-2.0
+
+ Unless required by applicable law or agreed to in writing, software
+ distributed under the License is distributed on an "AS IS" BASIS,
+ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ See the License for the specific language governing permissions and
+ limitations under the License.
+*/
+
+package events
+
+import (
+	"math"
+	"sync"
+	"time"
+
+	"github.com/apache/yunikorn-scheduler-interface/lib/go/si"
+)
+
+// default value of "latest" if there are no elements, helps in GetLatestEntries()
+const latestUnset int64 = math.MinInt64
+
+var now = time.Now
+
+// eventRingBuffer A specialized circular buffer to store event objects.
+//
+// Unlike to regular circular buffers, existing entries are never directly removed and new entries can be added if the buffer is full.
+// In this case, the oldest entry is overwritten and can be collected by the GC.
+//
+// Retrieving the records can be achieved with GetLatestEntriesCount, GetLatestEntries and GetEventsFromPosition.
+type eventRingBuffer struct {
+	events   []*si.EventRecord
+	capacity int
+	idx      int
+	latest   int64
+	full     bool
+	sync.RWMutex
+}
+
+// Add adds an event to the ring buffer. If the buffer is full, the oldest element is overwritten.
+// This method never fails.
+func (e *eventRingBuffer) Add(event *si.EventRecord) {
+	e.Lock()
+	defer e.Unlock()
+
+	e.events[e.idx] = event
+	e.idx = e.next(e.idx)
+	if e.idx == 0 {
+		// wrapped
+		e.full = true
+	}
+	e.latest = event.TimestampNano
+}
+
+// GetLatestEntriesCount returns most recent items. The amount is defined by "count".
+func (e *eventRingBuffer) GetLatestEntriesCount(count int) []*si.EventRecord {
+	e.RLock()
+	defer e.RUnlock()
+
+	if !e.full && e.idx == 0 {
+		return nil
+	}
+
+	records := make([]*si.EventRecord, 0, count)
+	var stop int
+	if e.full {
+		stop = e.idx
+	} else {
+		stop = 0
+	}
+	for i := e.prev(e.idx); ; {
+		records = append(records, e.events[i])
+		if len(records) == count || i == stop {
+			reverse(records)
+			return records
+		}
+
+		i = e.prev(i)
+	}
+}
+
+// GetLatestEntries returns the most recent items whose age is younger than the current time minus interval.
+func (e *eventRingBuffer) GetLatestEntries(interval time.Duration) []*si.EventRecord {

Review Comment:
   I think we should remove this method entirely.



##########
pkg/events/event_ringbuffer.go:
##########
@@ -0,0 +1,167 @@
+/*
+ Licensed to the Apache Software Foundation (ASF) under one
+ or more contributor license agreements.  See the NOTICE file
+ distributed with this work for additional information
+ regarding copyright ownership.  The ASF licenses this file
+ to you under the Apache License, Version 2.0 (the
+ "License"); you may not use this file except in compliance
+ with the License.  You may obtain a copy of the License at
+
+     http://www.apache.org/licenses/LICENSE-2.0
+
+ Unless required by applicable law or agreed to in writing, software
+ distributed under the License is distributed on an "AS IS" BASIS,
+ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ See the License for the specific language governing permissions and
+ limitations under the License.
+*/
+
+package events
+
+import (
+	"math"
+	"sync"
+	"time"
+
+	"github.com/apache/yunikorn-scheduler-interface/lib/go/si"
+)
+
+// default value of "latest" if there are no elements, helps in GetLatestEntries()
+const latestUnset int64 = math.MinInt64
+
+var now = time.Now
+
+// eventRingBuffer A specialized circular buffer to store event objects.
+//
+// Unlike to regular circular buffers, existing entries are never directly removed and new entries can be added if the buffer is full.
+// In this case, the oldest entry is overwritten and can be collected by the GC.
+//
+// Retrieving the records can be achieved with GetLatestEntriesCount, GetLatestEntries and GetEventsFromPosition.
+type eventRingBuffer struct {
+	events   []*si.EventRecord
+	capacity int
+	idx      int
+	latest   int64
+	full     bool
+	sync.RWMutex
+}
+
+// Add adds an event to the ring buffer. If the buffer is full, the oldest element is overwritten.
+// This method never fails.
+func (e *eventRingBuffer) Add(event *si.EventRecord) {
+	e.Lock()
+	defer e.Unlock()
+
+	e.events[e.idx] = event
+	e.idx = e.next(e.idx)
+	if e.idx == 0 {
+		// wrapped
+		e.full = true
+	}
+	e.latest = event.TimestampNano
+}
+
+// GetLatestEntriesCount returns most recent items. The amount is defined by "count".
+func (e *eventRingBuffer) GetLatestEntriesCount(count int) []*si.EventRecord {
+	e.RLock()
+	defer e.RUnlock()
+
+	if !e.full && e.idx == 0 {
+		return nil
+	}
+
+	records := make([]*si.EventRecord, 0, count)
+	var stop int
+	if e.full {
+		stop = e.idx
+	} else {
+		stop = 0
+	}
+	for i := e.prev(e.idx); ; {

Review Comment:
   This can be optimized a lot. We know the number of elements we are returning, so we can pre-size the slice. We can avoid the reverse() call if we change the semantics to return them in the original order (let the client handle reverse if it wants). Finally, we can avoid the iterative copying by copying the portion (if any) of the slice that is before the head pointer in the buffer separately from the portion after the head pointer. This allows more-efficient copy primitives to be used by the system.



##########
pkg/events/event_ringbuffer.go:
##########
@@ -0,0 +1,167 @@
+/*
+ Licensed to the Apache Software Foundation (ASF) under one
+ or more contributor license agreements.  See the NOTICE file
+ distributed with this work for additional information
+ regarding copyright ownership.  The ASF licenses this file
+ to you under the Apache License, Version 2.0 (the
+ "License"); you may not use this file except in compliance
+ with the License.  You may obtain a copy of the License at
+
+     http://www.apache.org/licenses/LICENSE-2.0
+
+ Unless required by applicable law or agreed to in writing, software
+ distributed under the License is distributed on an "AS IS" BASIS,
+ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ See the License for the specific language governing permissions and
+ limitations under the License.
+*/
+
+package events
+
+import (
+	"math"
+	"sync"
+	"time"
+
+	"github.com/apache/yunikorn-scheduler-interface/lib/go/si"
+)
+
+// default value of "latest" if there are no elements, helps in GetLatestEntries()
+const latestUnset int64 = math.MinInt64
+
+var now = time.Now
+
+// eventRingBuffer A specialized circular buffer to store event objects.
+//
+// Unlike to regular circular buffers, existing entries are never directly removed and new entries can be added if the buffer is full.
+// In this case, the oldest entry is overwritten and can be collected by the GC.
+//
+// Retrieving the records can be achieved with GetLatestEntriesCount, GetLatestEntries and GetEventsFromPosition.
+type eventRingBuffer struct {
+	events   []*si.EventRecord
+	capacity int
+	idx      int
+	latest   int64
+	full     bool
+	sync.RWMutex
+}
+
+// Add adds an event to the ring buffer. If the buffer is full, the oldest element is overwritten.
+// This method never fails.
+func (e *eventRingBuffer) Add(event *si.EventRecord) {
+	e.Lock()
+	defer e.Unlock()
+
+	e.events[e.idx] = event
+	e.idx = e.next(e.idx)
+	if e.idx == 0 {
+		// wrapped
+		e.full = true
+	}
+	e.latest = event.TimestampNano
+}
+
+// GetLatestEntriesCount returns most recent items. The amount is defined by "count".
+func (e *eventRingBuffer) GetLatestEntriesCount(count int) []*si.EventRecord {
+	e.RLock()
+	defer e.RUnlock()
+
+	if !e.full && e.idx == 0 {
+		return nil
+	}
+
+	records := make([]*si.EventRecord, 0, count)
+	var stop int
+	if e.full {
+		stop = e.idx
+	} else {
+		stop = 0
+	}
+	for i := e.prev(e.idx); ; {
+		records = append(records, e.events[i])
+		if len(records) == count || i == stop {
+			reverse(records)
+			return records
+		}
+
+		i = e.prev(i)
+	}
+}
+
+// GetLatestEntries returns the most recent items whose age is younger than the current time minus interval.
+func (e *eventRingBuffer) GetLatestEntries(interval time.Duration) []*si.EventRecord {
+	e.RLock()
+	defer e.RUnlock()
+
+	unixNow := now().UnixNano()
+	startTime := unixNow - interval.Nanoseconds()
+
+	if (!e.full && e.idx == 0) || (startTime > e.latest) {
+		return nil
+	}
+
+	var start, count int
+	if e.full {
+		count = e.capacity
+		start = e.idx
+	} else {
+		count = e.idx
+		start = 0
+	}
+
+	records := make([]*si.EventRecord, 0)
+	for i, c := start, 0; c != count; c++ {
+		if e.events[i].TimestampNano >= startTime {
+			records = append(records, e.events[i])
+		}
+
+		next := e.next(i)
+		i = next
+	}
+
+	return records
+}
+
+func (e *eventRingBuffer) GetEventsFromPosition(pos int) []*si.EventRecord {

Review Comment:
   Also, we should probably just combine this with GetLatestEntriesCount() (i.e. GetLatestEntries(pos, count)). Pos == 0 could be used if all values are requested. Also, if we return ([]*si.EventRecord, bool ok) we can mark if the requested data overflowed (i.e. pos was not within the result set). 



##########
pkg/events/event_ringbuffer.go:
##########
@@ -0,0 +1,167 @@
+/*
+ Licensed to the Apache Software Foundation (ASF) under one
+ or more contributor license agreements.  See the NOTICE file
+ distributed with this work for additional information
+ regarding copyright ownership.  The ASF licenses this file
+ to you under the Apache License, Version 2.0 (the
+ "License"); you may not use this file except in compliance
+ with the License.  You may obtain a copy of the License at
+
+     http://www.apache.org/licenses/LICENSE-2.0
+
+ Unless required by applicable law or agreed to in writing, software
+ distributed under the License is distributed on an "AS IS" BASIS,
+ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ See the License for the specific language governing permissions and
+ limitations under the License.
+*/
+
+package events
+
+import (
+	"math"
+	"sync"
+	"time"
+
+	"github.com/apache/yunikorn-scheduler-interface/lib/go/si"
+)
+
+// default value of "latest" if there are no elements, helps in GetLatestEntries()
+const latestUnset int64 = math.MinInt64
+
+var now = time.Now
+
+// eventRingBuffer A specialized circular buffer to store event objects.
+//
+// Unlike to regular circular buffers, existing entries are never directly removed and new entries can be added if the buffer is full.
+// In this case, the oldest entry is overwritten and can be collected by the GC.
+//
+// Retrieving the records can be achieved with GetLatestEntriesCount, GetLatestEntries and GetEventsFromPosition.
+type eventRingBuffer struct {
+	events   []*si.EventRecord
+	capacity int
+	idx      int
+	latest   int64
+	full     bool
+	sync.RWMutex
+}
+
+// Add adds an event to the ring buffer. If the buffer is full, the oldest element is overwritten.
+// This method never fails.
+func (e *eventRingBuffer) Add(event *si.EventRecord) {
+	e.Lock()
+	defer e.Unlock()
+
+	e.events[e.idx] = event
+	e.idx = e.next(e.idx)
+	if e.idx == 0 {
+		// wrapped
+		e.full = true
+	}
+	e.latest = event.TimestampNano
+}
+
+// GetLatestEntriesCount returns most recent items. The amount is defined by "count".
+func (e *eventRingBuffer) GetLatestEntriesCount(count int) []*si.EventRecord {
+	e.RLock()
+	defer e.RUnlock()
+
+	if !e.full && e.idx == 0 {
+		return nil
+	}
+
+	records := make([]*si.EventRecord, 0, count)
+	var stop int
+	if e.full {
+		stop = e.idx
+	} else {
+		stop = 0
+	}
+	for i := e.prev(e.idx); ; {
+		records = append(records, e.events[i])
+		if len(records) == count || i == stop {
+			reverse(records)
+			return records
+		}
+
+		i = e.prev(i)
+	}
+}
+
+// GetLatestEntries returns the most recent items whose age is younger than the current time minus interval.
+func (e *eventRingBuffer) GetLatestEntries(interval time.Duration) []*si.EventRecord {
+	e.RLock()
+	defer e.RUnlock()
+
+	unixNow := now().UnixNano()
+	startTime := unixNow - interval.Nanoseconds()
+
+	if (!e.full && e.idx == 0) || (startTime > e.latest) {
+		return nil
+	}
+
+	var start, count int
+	if e.full {
+		count = e.capacity
+		start = e.idx
+	} else {
+		count = e.idx
+		start = 0
+	}
+
+	records := make([]*si.EventRecord, 0)
+	for i, c := start, 0; c != count; c++ {
+		if e.events[i].TimestampNano >= startTime {
+			records = append(records, e.events[i])
+		}
+
+		next := e.next(i)
+		i = next
+	}
+
+	return records
+}
+
+func (e *eventRingBuffer) GetEventsFromPosition(pos int) []*si.EventRecord {

Review Comment:
   pos should probably be uint64 to avoid overflow. 



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