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simplify logic in queue's GetBroadcasts #301

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simplify logic in queue's GetBroadcasts #301

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102 changes: 24 additions & 78 deletions queue.go
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Original file line number Diff line number Diff line change
Expand Up @@ -268,24 +268,6 @@ func (q *TransmitLimitedQueue) addItem(cur *limitedBroadcast) {
}
}

// getTransmitRange returns a pair of min/max values for transmit values
// represented by the current queue contents. Both values represent actual
// transmit values on the interval [0, len). You must already hold the mutex.
func (q *TransmitLimitedQueue) getTransmitRange() (minTransmit, maxTransmit int) {
if q.lenLocked() == 0 {
return 0, 0
}
minItem, maxItem := q.tq.Min(), q.tq.Max()
if minItem == nil || maxItem == nil {
return 0, 0
}

min := minItem.(*limitedBroadcast).transmits
max := maxItem.(*limitedBroadcast).transmits

return min, max
}

// GetBroadcasts is used to get a number of broadcasts, up to a byte limit
// and applying a per-message overhead as provided.
func (q *TransmitLimitedQueue) GetBroadcasts(overhead, limit int) [][]byte {
Expand All @@ -302,76 +284,40 @@ func (q *TransmitLimitedQueue) GetBroadcasts(overhead, limit int) [][]byte {
var (
bytesUsed int
toSend [][]byte
reinsert []*limitedBroadcast
picked []*limitedBroadcast
)

// Visit fresher items first, but only look at stuff that will fit.
// We'll go tier by tier, grabbing the largest items first.
minTr, maxTr := q.getTransmitRange()
for transmits := minTr; transmits <= maxTr; /*do not advance automatically*/ {
free := int64(limit - bytesUsed - overhead)
var lb *limitedBroadcast
var free int64
q.tq.Ascend(func(item btree.Item) bool {
lb = item.(*limitedBroadcast)
free = int64(limit - bytesUsed - overhead)
if free <= 0 {
break // bail out early
}

// Search for the least element on a given tier (by transmit count) as
// defined in the limitedBroadcast.Less function that will fit into our
// remaining space.
greaterOrEqual := &limitedBroadcast{
transmits: transmits,
msgLen: free,
id: math.MaxInt64,
}
lessThan := &limitedBroadcast{
transmits: transmits + 1,
msgLen: math.MaxInt64,
id: math.MaxInt64,
return false // bail out early
}
var keep *limitedBroadcast
q.tq.AscendRange(greaterOrEqual, lessThan, func(item btree.Item) bool {
cur := item.(*limitedBroadcast)
// Check if this is within our limits
if int64(len(cur.b.Message())) > free {
// If this happens it's a bug in the datastructure or
// surrounding use doing something like having len(Message())
// change over time. There's enough going on here that it's
// probably sane to just skip it and move on for now.
return true
}
keep = cur
return false
})
if keep == nil {
// No more items of an appropriate size in the tier.
transmits++
continue
if int64(len(lb.b.Message())) > free {
return true // continue to next message
}

msg := keep.b.Message()

// Add to slice to send
bytesUsed += overhead + len(msg)
// msg ok to broadcast
msg := lb.b.Message()
toSend = append(toSend, msg)
bytesUsed += overhead + len(msg)
picked = append(picked, lb)
return true
})

// Check if we should stop transmission
q.deleteItem(keep)
if keep.transmits+1 >= transmitLimit {
keep.b.Finished()
// delete the picked message from queue.
// check the transmitted times
// to decide whether to finish or to continue transmission
for _, lb := range picked {
q.deleteItem(lb)
lb.transmits++
if lb.transmits >= transmitLimit {
lb.b.Finished()
} else {
// We need to bump this item down to another transmit tier, but
// because it would be in the same direction that we're walking the
// tiers, we will have to delay the reinsertion until we are
// finished our search. Otherwise we'll possibly re-add the message
// when we ascend to the next tier.
keep.transmits++
reinsert = append(reinsert, keep)
q.addItem(lb)
}
}

for _, cur := range reinsert {
q.addItem(cur)
}

return toSend
}

Expand Down
51 changes: 39 additions & 12 deletions queue_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -4,6 +4,7 @@
package memberlist

import (
"strings"
"testing"

"github.com/google/btree"
Expand Down Expand Up @@ -114,39 +115,65 @@ func TestTransmitLimited_GetBroadcasts(t *testing.T) {
}

func TestTransmitLimited_GetBroadcasts_Limit(t *testing.T) {
q := &TransmitLimitedQueue{RetransmitMult: 1, NumNodes: func() int { return 10 }}
q := &TransmitLimitedQueue{RetransmitMult: 1, NumNodes: func() int { return 100 }}

require.Equal(t, int64(0), q.idGen, "the id generator seed starts at zero")
require.Equal(t, 2, retransmitLimit(q.RetransmitMult, q.NumNodes()), "sanity check transmit limits")
require.Equal(t, 3, retransmitLimit(q.RetransmitMult, q.NumNodes()), "sanity check transmit limits")

// 18 bytes per message
q.QueueBroadcast(&memberlistBroadcast{"test", []byte("1. this is a test."), nil})
q.QueueBroadcast(&memberlistBroadcast{"foo", []byte("2. this is a test."), nil})
q.QueueBroadcast(&memberlistBroadcast{"bar", []byte("3. this is a test."), nil})
q.QueueBroadcast(&memberlistBroadcast{"baz", []byte("4. this is a test."), nil})
q.queueBroadcast(&memberlistBroadcast{"test", []byte("1. this is a test."), nil}, 1)
q.queueBroadcast(&memberlistBroadcast{"foo", []byte("2. this is a test."), nil}, 1)
// 54 bytes per message
q.queueBroadcast(&memberlistBroadcast{"bar", []byte(strings.Repeat("3. this is a test.", 3)), nil}, 0)
q.queueBroadcast(&memberlistBroadcast{"baz", []byte(strings.Repeat("4. this is a test.", 3)), nil}, 1)

require.Equal(t, int64(4), q.idGen, "we handed out 4 IDs")

dump := q.orderedView(false)
if dump[0].b.(*memberlistBroadcast).node != "bar" {
t.Fatalf("missing bar")
}
if dump[1].b.(*memberlistBroadcast).node != "baz" {
t.Fatalf("missing baz")
}
if dump[2].b.(*memberlistBroadcast).node != "foo" {
t.Fatalf("missing foo")
}
if dump[3].b.(*memberlistBroadcast).node != "test" {
t.Fatalf("missing test")
}

// 3 byte overhead, should only get 3 messages back
partial1 := q.GetBroadcasts(3, 80)
partial1 := q.GetBroadcasts(3, 99)
require.Equal(t, 3, len(partial1), "missing messages: %v", prettyPrintMessages(partial1))

require.Equal(t, int64(4), q.idGen, "id generator doesn't reset until empty")

partial2 := q.GetBroadcasts(3, 80)
partial2 := q.GetBroadcasts(3, 99)
require.Equal(t, 3, len(partial2), "missing messages: %v", prettyPrintMessages(partial2))

require.Equal(t, int64(4), q.idGen, "id generator doesn't reset until empty")

// Only two not expired
partial3 := q.GetBroadcasts(3, 80)
require.Equal(t, 2, len(partial3), "missing messages: %v", prettyPrintMessages(partial3))
partial3 := q.GetBroadcasts(3, 99)
require.Equal(t, 1, len(partial3), "missing messages: %v", prettyPrintMessages(partial3))

require.Equal(t, int64(4), q.idGen, "id generator doesn't reset until empty")
// Only two not expired
partial4 := q.GetBroadcasts(3, 99)
require.Equal(t, 1, len(partial4), "missing messages: %v", prettyPrintMessages(partial3))

require.Equal(t, int64(4), q.idGen, "id generator doesn't reset until empty")

// Only one not expired
partial5 := q.GetBroadcasts(3, 99)
require.Equal(t, 1, len(partial5), "missing messages: %v", prettyPrintMessages(partial5))

require.Equal(t, int64(0), q.idGen, "id generator resets on empty")

// Should get nothing
partial5 := q.GetBroadcasts(3, 80)
require.Equal(t, 0, len(partial5), "missing messages: %v", prettyPrintMessages(partial5))
partial6 := q.GetBroadcasts(3, 99)
require.Equal(t, 0, len(partial6), "missing messages: %v", prettyPrintMessages(partial6))

require.Equal(t, int64(0), q.idGen, "id generator resets on empty")
}
Expand Down