From 798dd5ab3c8f07e671e20fb5151d22d3773584b6 Mon Sep 17 00:00:00 2001
From: Maxim Ivanov <maxim@heroiclabs.com>
Date: Thu, 13 Oct 2022 12:47:52 +0100
Subject: [PATCH] Account party only once when finding candidates to remove to
 round down to CountMultiple. (#929)

---
 server/matchmaker.go | 32 ++++++++++++++++++++++----------
 1 file changed, 22 insertions(+), 10 deletions(-)

diff --git a/server/matchmaker.go b/server/matchmaker.go
index 636249189..208f7ac38 100644
--- a/server/matchmaker.go
+++ b/server/matchmaker.go
@@ -201,13 +201,19 @@ type LocalMatchmaker struct {
 	matchedEntriesFn func([][]*MatchmakerEntry)
 	batch            *index.Batch
 	indexWriter      *bluge.Writer
-	sessionTickets   map[string]map[string]struct{}
-	partyTickets     map[string]map[string]struct{}
-	entries          map[string][]*MatchmakerEntry
-	indexes          map[string]*MatchmakerIndex
-	activeIndexes    map[string]*MatchmakerIndex
-	revCache         map[string]map[string]bool
-	revThresholdFn   func() *time.Timer
+	// All tickets for a session ID.
+	sessionTickets map[string]map[string]struct{}
+	// All tickets for a party ID.
+	partyTickets map[string]map[string]struct{}
+	// All entries for a given ticket.
+	entries map[string][]*MatchmakerEntry
+	// Index for each ticket.
+	indexes map[string]*MatchmakerIndex
+	// Indexes that have not yet reached their max interval count.
+	activeIndexes map[string]*MatchmakerIndex
+	// Reverse lookup cache for mutual matching.
+	revCache       map[string]map[string]bool
+	revThresholdFn func() *time.Timer
 }
 
 func NewLocalMatchmaker(logger, startupLogger *zap.Logger, config Config, router MessageRouter, metrics Metrics, runtime *Runtime) Matchmaker {
@@ -486,6 +492,7 @@ func (m *LocalMatchmaker) Process() {
 					break
 				}
 			}
+			// Either processing first hit, or current hit entries combined with previous hits may tip over index.MaxCount.
 			if foundCombo == nil {
 				entryCombo := make([]*MatchmakerEntry, len(entries))
 				copy(entryCombo, entries)
@@ -505,15 +512,20 @@ func (m *LocalMatchmaker) Process() {
 					// The size of the combination being considered does not satisfy the count multiple.
 					// Attempt to adjust the combo by removing the smallest possible number of entries.
 					// Prefer keeping entries that have been in the matchmaker the longest, if possible.
-					eligibleIndexes := make([]*MatchmakerIndex, 0, len(foundCombo))
+					eligibleIndexesUniq := make(map[*MatchmakerIndex]struct{}, len(foundCombo))
 					for _, e := range foundCombo {
 						// Only tickets individually less <= the removable size are considered.
 						// For example removing a party of 3 when we're only looking to remove 2 is not allowed.
 						if foundIndex, ok := m.indexes[e.Ticket]; ok && foundIndex.Count <= rem {
-							eligibleIndexes = append(eligibleIndexes, foundIndex)
+							eligibleIndexesUniq[foundIndex] = struct{}{}
 						}
 					}
 
+					eligibleIndexes := make([]*MatchmakerIndex, 0, len(eligibleIndexesUniq))
+					for _, egi := range eligibleIndexes {
+						eligibleIndexes = append(eligibleIndexes, egi)
+					}
+
 					eligibleGroups := groupIndexes(eligibleIndexes, rem)
 					if len(eligibleGroups) <= 0 {
 						// No possible combination to remove, unlikely but guard.
@@ -530,7 +542,7 @@ func (m *LocalMatchmaker) Process() {
 								foundCombo[i] = foundCombo[len(foundCombo)-1]
 								foundCombo[len(foundCombo)-1] = nil
 								foundCombo = foundCombo[:len(foundCombo)-1]
-								break
+								i--
 							}
 						}
 					}
-- 
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