Merge pull request #2870 from weaveworks/sliced-maps

Re-implement LatestMap as a sorted slice for better performance

extras/generate_latest_map

@@ -19,11 +19,12 @@ function generate_header() {
     package report
 
     import (
+		"bytes"
         "fmt"
+		"sort"
         "time"
 
         "github.com/ugorji/go/codec"
-        "github.com/weaveworks/ps"
     )
 EOF
 }
@@ -35,7 +36,6 @@ function generate_latest_map() {
     local lowercase_data_type="${data_type,}"
     local entry_type="${lowercase_data_type}LatestEntry"
     local latest_map_type="${uppercase_data_type}LatestMap"
-    local empty_latest_map_variable="empty${latest_map_type}"
     local make_function="Make${latest_map_type}"
 
     # shellcheck disable=SC2016
@@ -45,6 +45,7 @@ function generate_latest_map() {
 
     cat <<EOF >>"${out_file}"
     type ${entry_type} struct {
+        key       string
         Timestamp time.Time    ${json_timestamp}
         Value     ${data_type} ${json_value}
         dummySelfer
@@ -60,31 +61,51 @@ function generate_latest_map() {
         return e.Timestamp.Equal(e2.Timestamp) && e.Value == e2.Value
     }
 
-    // ${latest_map_type} holds latest ${data_type} instances.
-    type ${latest_map_type} struct { ps.Map }
-
-    var ${empty_latest_map_variable} = ${latest_map_type}{ps.NewMap()}
+    // ${latest_map_type} holds latest ${data_type} instances, as a slice sorted by key.
+    type ${latest_map_type} struct { entries []${entry_type} }
 
     // ${make_function} makes an empty ${latest_map_type}.
     func ${make_function}() ${latest_map_type} {
-        return ${empty_latest_map_variable}
+        return ${latest_map_type}{}
     }
 
     // Size returns the number of elements.
     func (m ${latest_map_type}) Size() int {
-        if m.Map == nil {
-	        return 0
-        }
-        return m.Map.Size()
+        return len(m.entries)
     }
 
     // Merge produces a fresh ${latest_map_type} containing the keys from both inputs.
     // When both inputs contain the same key, the newer value is used.
-    func (m ${latest_map_type}) Merge(other ${latest_map_type}) ${latest_map_type} {
-        output := mergeMaps(m.Map, other.Map, func(a, b interface{}) bool {
-	        return a.(*${entry_type}).Timestamp.Before(b.(*${entry_type}).Timestamp)
-        })
-        return ${latest_map_type}{output}
+    func (m ${latest_map_type}) Merge(n ${latest_map_type}) ${latest_map_type} {
+        switch {
+        case m.entries == nil:
+            return n
+        case n.entries == nil:
+            return m
+        }
+        out := make([]${entry_type}, 0, len(m.entries)+len(n.entries))
+
+        i, j := 0, 0
+        for i < len(m.entries) {
+            switch {
+            case j >= len(n.entries) || m.entries[i].key < n.entries[j].key:
+                out = append(out, m.entries[i])
+                i++
+            case m.entries[i].key == n.entries[j].key:
+                if m.entries[i].Timestamp.Before(n.entries[j].Timestamp) {
+                    out = append(out, n.entries[j])
+                } else {
+                    out = append(out, m.entries[i])
+                }
+                i++
+                j++
+            default:
+                out = append(out, n.entries[j])
+                j++
+            }
+        }
+        out = append(out, n.entries[j:]...)
+        return ${latest_map_type}{out}
     }
 
     // Lookup the value for the given key.
@@ -99,65 +120,135 @@ function generate_latest_map() {
 
     // LookupEntry returns the raw entry for the given key.
     func (m ${latest_map_type}) LookupEntry(key string) (${data_type}, time.Time, bool) {
-        if m.Map == nil {
-	        var zero ${data_type}
-	        return zero, time.Time{}, false
+        i := sort.Search(len(m.entries), func(i int) bool {
+            return m.entries[i].key >= key
+        })
+        if i < len(m.entries) && m.entries[i].key == key {
+            return m.entries[i].Value, m.entries[i].Timestamp, true
         }
-        value, ok := m.Map.Lookup(key)
-        if !ok {
-	        var zero ${data_type}
-	        return zero, time.Time{}, false
+        var zero ${data_type}
+        return zero, time.Time{}, false
+    }
+
+    // locate the position where key should go, and make room for it if not there already
+    func (m *${latest_map_type}) locate(key string) int {
+        i := sort.Search(len(m.entries), func(i int) bool {
+            return m.entries[i].key >= key
+        })
+        // i is now the position where key should go, either at the end or in the middle
+        if i == len(m.entries) || m.entries[i].key != key {
+            m.entries = append(m.entries, ${entry_type}{})
+            copy(m.entries[i+1:], m.entries[i:])
         }
-        e := value.(*${entry_type})
-        return e.Value, e.Timestamp, true
+        return i
     }
 
     // Set the value for the given key.
     func (m ${latest_map_type}) Set(key string, timestamp time.Time, value ${data_type}) ${latest_map_type} {
-        if m.Map == nil {
-	        m.Map = ps.NewMap()
+        i := sort.Search(len(m.entries), func(i int) bool {
+            return m.entries[i].key >= key
+        })
+        // i is now the position where key should go, either at the end or in the middle
+        oldEntries := m.entries
+        if i == len(m.entries) {
+            m.entries = make([]${entry_type}, len(oldEntries)+1)
+            copy(m.entries, oldEntries)
+        } else if m.entries[i].key == key {
+            m.entries = make([]${entry_type}, len(oldEntries))
+            copy(m.entries, oldEntries)
+        } else {
+            m.entries = make([]${entry_type}, len(oldEntries)+1)
+            copy(m.entries, oldEntries[:i])
+            copy(m.entries[i+1:], oldEntries[i:])
         }
-        return ${latest_map_type}{m.Map.Set(key, &${entry_type}{Timestamp: timestamp, Value: value})}
+        m.entries[i] = ${entry_type}{key: key, Timestamp: timestamp, Value: value}
+        return m
     }
 
     // ForEach executes fn on each key value pair in the map.
     func (m ${latest_map_type}) ForEach(fn func(k string, timestamp time.Time, v ${data_type})) {
-        if m.Map != nil {
-	        m.Map.ForEach(func(key string, value interface{}) {
-		        fn(key, value.(*${entry_type}).Timestamp, value.(*${entry_type}).Value)
-	        })
+        for _, value := range m.entries {
+            fn(value.key, value.Timestamp, value.Value)
         }
     }
 
     // String returns the ${latest_map_type}'s string representation.
     func (m ${latest_map_type}) String() string {
-        return mapToString(m.Map)
+        buf := bytes.NewBufferString("{")
+        for _, val := range m.entries {
+            fmt.Fprintf(buf, "%s: %s,\n", val.key, val)
+        }
+        fmt.Fprintf(buf, "}")
+        return buf.String()
     }
 
     // DeepEqual tests equality with other ${latest_map_type}.
     func (m ${latest_map_type}) DeepEqual(n ${latest_map_type}) bool {
-        return mapEqual(m.Map, n.Map, func(val, otherValue interface{}) bool {
-	        return val.(*${entry_type}).Equal(otherValue.(*${entry_type}))
-        })
+        if m.Size() != n.Size() {
+            return false
+        }
+        for i := range m.entries {
+            if m.entries[i].key != n.entries[i].key || !m.entries[i].Equal(&n.entries[i]) {
+                return false
+            }
+        }
+        return true
     }
 
     // CodecEncodeSelf implements codec.Selfer.
+    // Duplicates the output for a built-in map without generating an
+    // intermediate copy of the data structure, to save time.  Note this
+    // means we are using undocumented, internal APIs, which could break
+    // in the future.  See https://github.com/weaveworks/scope/pull/1709
+    // for more information.
     func (m *${latest_map_type}) CodecEncodeSelf(encoder *codec.Encoder) {
-        mapWrite(m.Map, encoder, func(encoder *codec.Encoder, val interface{}) {
-            val.(*${entry_type}).CodecEncodeSelf(encoder)
-        })
+        z, r := codec.GenHelperEncoder(encoder)
+        if m.entries == nil {
+            r.EncodeNil()
+            return
+        }
+        r.EncodeMapStart(m.Size())
+        for _, val := range m.entries {
+            z.EncSendContainerState(containerMapKey)
+            r.EncodeString(cUTF8, val.key)
+            z.EncSendContainerState(containerMapValue)
+            val.CodecEncodeSelf(encoder)
+        }
+        z.EncSendContainerState(containerMapEnd)
     }
 
     // CodecDecodeSelf implements codec.Selfer.
+    // Decodes the input as for a built-in map, without creating an
+    // intermediate copy of the data structure to save time. Uses
+    // undocumented, internal APIs as for CodecEncodeSelf.
     func (m *${latest_map_type}) CodecDecodeSelf(decoder *codec.Decoder) {
-        out := mapRead(decoder, func(isNil bool) interface{} {
-	        value := &${entry_type}{}
-	        if !isNil {
-		        value.CodecDecodeSelf(decoder)
-	        }
-	        return value
-        })
-        *m = ${latest_map_type}{out}
+        m.entries = nil
+        z, r := codec.GenHelperDecoder(decoder)
+        if r.TryDecodeAsNil() {
+            return
+        }
+
+        length := r.ReadMapStart()
+        if length > 0 {
+            m.entries = make([]${entry_type}, 0, length)
+        }
+        for i := 0; length < 0 || i < length; i++ {
+            if length < 0 && r.CheckBreak() {
+                break
+            }
+            z.DecSendContainerState(containerMapKey)
+            var key string
+            if !r.TryDecodeAsNil() {
+                key = r.DecodeString()
+            }
+            i := m.locate(key)
+            m.entries[i].key = key
+            z.DecSendContainerState(containerMapValue)
+            if !r.TryDecodeAsNil() {
+                m.entries[i].CodecDecodeSelf(decoder)
+            }
+        }
+        z.DecSendContainerState(containerMapEnd)
     }
 
     // MarshalJSON shouldn't be used, use CodecEncodeSelf instead.

report/latest_map_generated.go

@@ -4,14 +4,16 @@
 package report
 
 import (
+	"bytes"
 	"fmt"
+	"sort"
 	"time"
 
 	"github.com/ugorji/go/codec"
-	"github.com/weaveworks/ps"
 )
 
 type stringLatestEntry struct {
+	key       string
 	Timestamp time.Time `json:"timestamp"`
 	Value     string    `json:"value"`
 	dummySelfer
@@ -27,31 +29,51 @@ func (e *stringLatestEntry) Equal(e2 *stringLatestEntry) bool {
 	return e.Timestamp.Equal(e2.Timestamp) && e.Value == e2.Value
 }
 
-// StringLatestMap holds latest string instances.
-type StringLatestMap struct{ ps.Map }
-
-var emptyStringLatestMap = StringLatestMap{ps.NewMap()}
+// StringLatestMap holds latest string instances, as a slice sorted by key.
+type StringLatestMap struct{ entries []stringLatestEntry }
 
 // MakeStringLatestMap makes an empty StringLatestMap.
 func MakeStringLatestMap() StringLatestMap {
-	return emptyStringLatestMap
+	return StringLatestMap{}
 }
 
 // Size returns the number of elements.
 func (m StringLatestMap) Size() int {
-	if m.Map == nil {
-		return 0
-	}
-	return m.Map.Size()
+	return len(m.entries)
 }
 
 // Merge produces a fresh StringLatestMap containing the keys from both inputs.
 // When both inputs contain the same key, the newer value is used.
-func (m StringLatestMap) Merge(other StringLatestMap) StringLatestMap {
-	output := mergeMaps(m.Map, other.Map, func(a, b interface{}) bool {
-		return a.(*stringLatestEntry).Timestamp.Before(b.(*stringLatestEntry).Timestamp)
-	})
-	return StringLatestMap{output}
+func (m StringLatestMap) Merge(n StringLatestMap) StringLatestMap {
+	switch {
+	case m.entries == nil:
+		return n
+	case n.entries == nil:
+		return m
+	}
+	out := make([]stringLatestEntry, 0, len(m.entries)+len(n.entries))
+
+	i, j := 0, 0
+	for i < len(m.entries) {
+		switch {
+		case j >= len(n.entries) || m.entries[i].key < n.entries[j].key:
+			out = append(out, m.entries[i])
+			i++
+		case m.entries[i].key == n.entries[j].key:
+			if m.entries[i].Timestamp.Before(n.entries[j].Timestamp) {
+				out = append(out, n.entries[j])
+			} else {
+				out = append(out, m.entries[i])
+			}
+			i++
+			j++
+		default:
+			out = append(out, n.entries[j])
+			j++
+		}
+	}
+	out = append(out, n.entries[j:]...)
+	return StringLatestMap{out}
 }
 
 // Lookup the value for the given key.
@@ -66,65 +88,135 @@ func (m StringLatestMap) Lookup(key string) (string, bool) {
 
 // LookupEntry returns the raw entry for the given key.
 func (m StringLatestMap) LookupEntry(key string) (string, time.Time, bool) {
-	if m.Map == nil {
-		var zero string
-		return zero, time.Time{}, false
+	i := sort.Search(len(m.entries), func(i int) bool {
+		return m.entries[i].key >= key
+	})
+	if i < len(m.entries) && m.entries[i].key == key {
+		return m.entries[i].Value, m.entries[i].Timestamp, true
 	}
-	value, ok := m.Map.Lookup(key)
-	if !ok {
-		var zero string
-		return zero, time.Time{}, false
+	var zero string
+	return zero, time.Time{}, false
+}
+
+// locate the position where key should go, and make room for it if not there already
+func (m *StringLatestMap) locate(key string) int {
+	i := sort.Search(len(m.entries), func(i int) bool {
+		return m.entries[i].key >= key
+	})
+	// i is now the position where key should go, either at the end or in the middle
+	if i == len(m.entries) || m.entries[i].key != key {
+		m.entries = append(m.entries, stringLatestEntry{})
+		copy(m.entries[i+1:], m.entries[i:])
 	}
-	e := value.(*stringLatestEntry)
-	return e.Value, e.Timestamp, true
+	return i
 }
 
 // Set the value for the given key.
 func (m StringLatestMap) Set(key string, timestamp time.Time, value string) StringLatestMap {
-	if m.Map == nil {
-		m.Map = ps.NewMap()
+	i := sort.Search(len(m.entries), func(i int) bool {
+		return m.entries[i].key >= key
+	})
+	// i is now the position where key should go, either at the end or in the middle
+	oldEntries := m.entries
+	if i == len(m.entries) {
+		m.entries = make([]stringLatestEntry, len(oldEntries)+1)
+		copy(m.entries, oldEntries)
+	} else if m.entries[i].key == key {
+		m.entries = make([]stringLatestEntry, len(oldEntries))
+		copy(m.entries, oldEntries)
+	} else {
+		m.entries = make([]stringLatestEntry, len(oldEntries)+1)
+		copy(m.entries, oldEntries[:i])
+		copy(m.entries[i+1:], oldEntries[i:])
 	}
-	return StringLatestMap{m.Map.Set(key, &stringLatestEntry{Timestamp: timestamp, Value: value})}
+	m.entries[i] = stringLatestEntry{key: key, Timestamp: timestamp, Value: value}
+	return m
 }
 
 // ForEach executes fn on each key value pair in the map.
 func (m StringLatestMap) ForEach(fn func(k string, timestamp time.Time, v string)) {
-	if m.Map != nil {
-		m.Map.ForEach(func(key string, value interface{}) {
-			fn(key, value.(*stringLatestEntry).Timestamp, value.(*stringLatestEntry).Value)
-		})
+	for _, value := range m.entries {
+		fn(value.key, value.Timestamp, value.Value)
 	}
 }
 
 // String returns the StringLatestMap's string representation.
 func (m StringLatestMap) String() string {
-	return mapToString(m.Map)
+	buf := bytes.NewBufferString("{")
+	for _, val := range m.entries {
+		fmt.Fprintf(buf, "%s: %s,\n", val.key, val)
+	}
+	fmt.Fprintf(buf, "}")
+	return buf.String()
 }
 
 // DeepEqual tests equality with other StringLatestMap.
 func (m StringLatestMap) DeepEqual(n StringLatestMap) bool {
-	return mapEqual(m.Map, n.Map, func(val, otherValue interface{}) bool {
-		return val.(*stringLatestEntry).Equal(otherValue.(*stringLatestEntry))
-	})
+	if m.Size() != n.Size() {
+		return false
+	}
+	for i := range m.entries {
+		if m.entries[i].key != n.entries[i].key || !m.entries[i].Equal(&n.entries[i]) {
+			return false
+		}
+	}
+	return true
 }
 
 // CodecEncodeSelf implements codec.Selfer.
+// Duplicates the output for a built-in map without generating an
+// intermediate copy of the data structure, to save time.  Note this
+// means we are using undocumented, internal APIs, which could break
+// in the future.  See https://github.com/weaveworks/scope/pull/1709
+// for more information.
 func (m *StringLatestMap) CodecEncodeSelf(encoder *codec.Encoder) {
-	mapWrite(m.Map, encoder, func(encoder *codec.Encoder, val interface{}) {
-		val.(*stringLatestEntry).CodecEncodeSelf(encoder)
-	})
+	z, r := codec.GenHelperEncoder(encoder)
+	if m.entries == nil {
+		r.EncodeNil()
+		return
+	}
+	r.EncodeMapStart(m.Size())
+	for _, val := range m.entries {
+		z.EncSendContainerState(containerMapKey)
+		r.EncodeString(cUTF8, val.key)
+		z.EncSendContainerState(containerMapValue)
+		val.CodecEncodeSelf(encoder)
+	}
+	z.EncSendContainerState(containerMapEnd)
 }
 
 // CodecDecodeSelf implements codec.Selfer.
+// Decodes the input as for a built-in map, without creating an
+// intermediate copy of the data structure to save time. Uses
+// undocumented, internal APIs as for CodecEncodeSelf.
 func (m *StringLatestMap) CodecDecodeSelf(decoder *codec.Decoder) {
-	out := mapRead(decoder, func(isNil bool) interface{} {
-		value := &stringLatestEntry{}
-		if !isNil {
-			value.CodecDecodeSelf(decoder)
+	m.entries = nil
+	z, r := codec.GenHelperDecoder(decoder)
+	if r.TryDecodeAsNil() {
+		return
+	}
+
+	length := r.ReadMapStart()
+	if length > 0 {
+		m.entries = make([]stringLatestEntry, 0, length)
+	}
+	for i := 0; length < 0 || i < length; i++ {
+		if length < 0 && r.CheckBreak() {
+			break
 		}
-		return value
-	})
-	*m = StringLatestMap{out}
+		z.DecSendContainerState(containerMapKey)
+		var key string
+		if !r.TryDecodeAsNil() {
+			key = r.DecodeString()
+		}
+		i := m.locate(key)
+		m.entries[i].key = key
+		z.DecSendContainerState(containerMapValue)
+		if !r.TryDecodeAsNil() {
+			m.entries[i].CodecDecodeSelf(decoder)
+		}
+	}
+	z.DecSendContainerState(containerMapEnd)
 }
 
 // MarshalJSON shouldn't be used, use CodecEncodeSelf instead.
@@ -138,6 +230,7 @@ func (*StringLatestMap) UnmarshalJSON(b []byte) error {
 }
 
 type nodeControlDataLatestEntry struct {
+	key       string
 	Timestamp time.Time       `json:"timestamp"`
 	Value     NodeControlData `json:"value"`
 	dummySelfer
@@ -153,31 +246,51 @@ func (e *nodeControlDataLatestEntry) Equal(e2 *nodeControlDataLatestEntry) bool
 	return e.Timestamp.Equal(e2.Timestamp) && e.Value == e2.Value
 }
 
-// NodeControlDataLatestMap holds latest NodeControlData instances.
-type NodeControlDataLatestMap struct{ ps.Map }
-
-var emptyNodeControlDataLatestMap = NodeControlDataLatestMap{ps.NewMap()}
+// NodeControlDataLatestMap holds latest NodeControlData instances, as a slice sorted by key.
+type NodeControlDataLatestMap struct{ entries []nodeControlDataLatestEntry }
 
 // MakeNodeControlDataLatestMap makes an empty NodeControlDataLatestMap.
 func MakeNodeControlDataLatestMap() NodeControlDataLatestMap {
-	return emptyNodeControlDataLatestMap
+	return NodeControlDataLatestMap{}
 }
 
 // Size returns the number of elements.
 func (m NodeControlDataLatestMap) Size() int {
-	if m.Map == nil {
-		return 0
-	}
-	return m.Map.Size()
+	return len(m.entries)
 }
 
 // Merge produces a fresh NodeControlDataLatestMap containing the keys from both inputs.
 // When both inputs contain the same key, the newer value is used.
-func (m NodeControlDataLatestMap) Merge(other NodeControlDataLatestMap) NodeControlDataLatestMap {
-	output := mergeMaps(m.Map, other.Map, func(a, b interface{}) bool {
-		return a.(*nodeControlDataLatestEntry).Timestamp.Before(b.(*nodeControlDataLatestEntry).Timestamp)
-	})
-	return NodeControlDataLatestMap{output}
+func (m NodeControlDataLatestMap) Merge(n NodeControlDataLatestMap) NodeControlDataLatestMap {
+	switch {
+	case m.entries == nil:
+		return n
+	case n.entries == nil:
+		return m
+	}
+	out := make([]nodeControlDataLatestEntry, 0, len(m.entries)+len(n.entries))
+
+	i, j := 0, 0
+	for i < len(m.entries) {
+		switch {
+		case j >= len(n.entries) || m.entries[i].key < n.entries[j].key:
+			out = append(out, m.entries[i])
+			i++
+		case m.entries[i].key == n.entries[j].key:
+			if m.entries[i].Timestamp.Before(n.entries[j].Timestamp) {
+				out = append(out, n.entries[j])
+			} else {
+				out = append(out, m.entries[i])
+			}
+			i++
+			j++
+		default:
+			out = append(out, n.entries[j])
+			j++
+		}
+	}
+	out = append(out, n.entries[j:]...)
+	return NodeControlDataLatestMap{out}
 }
 
 // Lookup the value for the given key.
@@ -192,65 +305,135 @@ func (m NodeControlDataLatestMap) Lookup(key string) (NodeControlData, bool) {
 
 // LookupEntry returns the raw entry for the given key.
 func (m NodeControlDataLatestMap) LookupEntry(key string) (NodeControlData, time.Time, bool) {
-	if m.Map == nil {
-		var zero NodeControlData
-		return zero, time.Time{}, false
+	i := sort.Search(len(m.entries), func(i int) bool {
+		return m.entries[i].key >= key
+	})
+	if i < len(m.entries) && m.entries[i].key == key {
+		return m.entries[i].Value, m.entries[i].Timestamp, true
 	}
-	value, ok := m.Map.Lookup(key)
-	if !ok {
-		var zero NodeControlData
-		return zero, time.Time{}, false
+	var zero NodeControlData
+	return zero, time.Time{}, false
+}
+
+// locate the position where key should go, and make room for it if not there already
+func (m *NodeControlDataLatestMap) locate(key string) int {
+	i := sort.Search(len(m.entries), func(i int) bool {
+		return m.entries[i].key >= key
+	})
+	// i is now the position where key should go, either at the end or in the middle
+	if i == len(m.entries) || m.entries[i].key != key {
+		m.entries = append(m.entries, nodeControlDataLatestEntry{})
+		copy(m.entries[i+1:], m.entries[i:])
 	}
-	e := value.(*nodeControlDataLatestEntry)
-	return e.Value, e.Timestamp, true
+	return i
 }
 
 // Set the value for the given key.
 func (m NodeControlDataLatestMap) Set(key string, timestamp time.Time, value NodeControlData) NodeControlDataLatestMap {
-	if m.Map == nil {
-		m.Map = ps.NewMap()
+	i := sort.Search(len(m.entries), func(i int) bool {
+		return m.entries[i].key >= key
+	})
+	// i is now the position where key should go, either at the end or in the middle
+	oldEntries := m.entries
+	if i == len(m.entries) {
+		m.entries = make([]nodeControlDataLatestEntry, len(oldEntries)+1)
+		copy(m.entries, oldEntries)
+	} else if m.entries[i].key == key {
+		m.entries = make([]nodeControlDataLatestEntry, len(oldEntries))
+		copy(m.entries, oldEntries)
+	} else {
+		m.entries = make([]nodeControlDataLatestEntry, len(oldEntries)+1)
+		copy(m.entries, oldEntries[:i])
+		copy(m.entries[i+1:], oldEntries[i:])
 	}
-	return NodeControlDataLatestMap{m.Map.Set(key, &nodeControlDataLatestEntry{Timestamp: timestamp, Value: value})}
+	m.entries[i] = nodeControlDataLatestEntry{key: key, Timestamp: timestamp, Value: value}
+	return m
 }
 
 // ForEach executes fn on each key value pair in the map.
 func (m NodeControlDataLatestMap) ForEach(fn func(k string, timestamp time.Time, v NodeControlData)) {
-	if m.Map != nil {
-		m.Map.ForEach(func(key string, value interface{}) {
-			fn(key, value.(*nodeControlDataLatestEntry).Timestamp, value.(*nodeControlDataLatestEntry).Value)
-		})
+	for _, value := range m.entries {
+		fn(value.key, value.Timestamp, value.Value)
 	}
 }
 
 // String returns the NodeControlDataLatestMap's string representation.
 func (m NodeControlDataLatestMap) String() string {
-	return mapToString(m.Map)
+	buf := bytes.NewBufferString("{")
+	for _, val := range m.entries {
+		fmt.Fprintf(buf, "%s: %s,\n", val.key, val)
+	}
+	fmt.Fprintf(buf, "}")
+	return buf.String()
 }
 
 // DeepEqual tests equality with other NodeControlDataLatestMap.
 func (m NodeControlDataLatestMap) DeepEqual(n NodeControlDataLatestMap) bool {
-	return mapEqual(m.Map, n.Map, func(val, otherValue interface{}) bool {
-		return val.(*nodeControlDataLatestEntry).Equal(otherValue.(*nodeControlDataLatestEntry))
-	})
+	if m.Size() != n.Size() {
+		return false
+	}
+	for i := range m.entries {
+		if m.entries[i].key != n.entries[i].key || !m.entries[i].Equal(&n.entries[i]) {
+			return false
+		}
+	}
+	return true
 }
 
 // CodecEncodeSelf implements codec.Selfer.
+// Duplicates the output for a built-in map without generating an
+// intermediate copy of the data structure, to save time.  Note this
+// means we are using undocumented, internal APIs, which could break
+// in the future.  See https://github.com/weaveworks/scope/pull/1709
+// for more information.
 func (m *NodeControlDataLatestMap) CodecEncodeSelf(encoder *codec.Encoder) {
-	mapWrite(m.Map, encoder, func(encoder *codec.Encoder, val interface{}) {
-		val.(*nodeControlDataLatestEntry).CodecEncodeSelf(encoder)
-	})
+	z, r := codec.GenHelperEncoder(encoder)
+	if m.entries == nil {
+		r.EncodeNil()
+		return
+	}
+	r.EncodeMapStart(m.Size())
+	for _, val := range m.entries {
+		z.EncSendContainerState(containerMapKey)
+		r.EncodeString(cUTF8, val.key)
+		z.EncSendContainerState(containerMapValue)
+		val.CodecEncodeSelf(encoder)
+	}
+	z.EncSendContainerState(containerMapEnd)
 }
 
 // CodecDecodeSelf implements codec.Selfer.
+// Decodes the input as for a built-in map, without creating an
+// intermediate copy of the data structure to save time. Uses
+// undocumented, internal APIs as for CodecEncodeSelf.
 func (m *NodeControlDataLatestMap) CodecDecodeSelf(decoder *codec.Decoder) {
-	out := mapRead(decoder, func(isNil bool) interface{} {
-		value := &nodeControlDataLatestEntry{}
-		if !isNil {
-			value.CodecDecodeSelf(decoder)
+	m.entries = nil
+	z, r := codec.GenHelperDecoder(decoder)
+	if r.TryDecodeAsNil() {
+		return
+	}
+
+	length := r.ReadMapStart()
+	if length > 0 {
+		m.entries = make([]nodeControlDataLatestEntry, 0, length)
+	}
+	for i := 0; length < 0 || i < length; i++ {
+		if length < 0 && r.CheckBreak() {
+			break
 		}
-		return value
-	})
-	*m = NodeControlDataLatestMap{out}
+		z.DecSendContainerState(containerMapKey)
+		var key string
+		if !r.TryDecodeAsNil() {
+			key = r.DecodeString()
+		}
+		i := m.locate(key)
+		m.entries[i].key = key
+		z.DecSendContainerState(containerMapValue)
+		if !r.TryDecodeAsNil() {
+			m.entries[i].CodecDecodeSelf(decoder)
+		}
+	}
+	z.DecSendContainerState(containerMapEnd)
 }
 
 // MarshalJSON shouldn't be used, use CodecEncodeSelf instead.

report/latest_map_internal_test.go

@@ -72,7 +72,7 @@ func TestLatestMapDeepEquals(t *testing.T) {
 
 func nilStringLatestMap() StringLatestMap {
 	m := MakeStringLatestMap()
-	m.Map = nil
+	m.entries = nil
 	return m
 }
 
@@ -126,21 +126,18 @@ func TestLatestMapMerge(t *testing.T) {
 	}
 }
 
+func makeBenchmarkMap(start, finish int, timestamp time.Time) StringLatestMap {
+	ret := MakeStringLatestMap()
+	for i := start; i < finish; i++ {
+		ret = ret.Set(fmt.Sprint(i), timestamp, "1")
+	}
+	return ret
+}
+
 func BenchmarkLatestMapMerge(b *testing.B) {
-	var (
-		left  = MakeStringLatestMap()
-		right = MakeStringLatestMap()
-		now   = time.Now()
-	)
-
 	// two large maps with some overlap
-	for i := 0; i < 1000; i++ {
-		left = left.Set(fmt.Sprint(i), now, "1")
-	}
-	for i := 700; i < 1700; i++ {
-		right = right.Set(fmt.Sprint(i), now.Add(1*time.Minute), "1")
-	}
-
+	left := makeBenchmarkMap(0, 1000, time.Now())
+	right := makeBenchmarkMap(700, 1700, time.Now().Add(1*time.Minute))
 	b.ReportAllocs()
 	b.ResetTimer()
 	for i := 0; i < b.N; i++ {
@@ -148,6 +145,28 @@ func BenchmarkLatestMapMerge(b *testing.B) {
 	}
 }
 
+func BenchmarkLatestMapEncode(b *testing.B) {
+	map1 := makeBenchmarkMap(0, 1000, time.Now())
+	b.ReportAllocs()
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		buf := &bytes.Buffer{}
+		codec.NewEncoder(buf, &codec.MsgpackHandle{}).Encode(&map1)
+	}
+}
+
+func BenchmarkLatestMapDecode(b *testing.B) {
+	map1 := makeBenchmarkMap(0, 1000, time.Now())
+	buf := &bytes.Buffer{}
+	codec.NewEncoder(buf, &codec.MsgpackHandle{}).Encode(&map1)
+	b.ReportAllocs()
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		var map1 StringLatestMap
+		codec.NewDecoderBytes(buf.Bytes(), &codec.MsgpackHandle{}).Decode(&map1)
+	}
+}
+
 func TestLatestMapEncoding(t *testing.T) {
 	now := time.Now()
 	want := MakeStringLatestMap().