From 1e80e3ae654f5debfc3cad3fbd7dad3b30767852 Mon Sep 17 00:00:00 2001
From: vyzo <vyzo@hackzen.org>
Date: Thu, 6 Aug 2020 18:37:28 +0300
Subject: [PATCH] create maximal chains

Merge chains when gasPerf is non-descreasing (instead of increasing) to create maximal chains.
This also obviates the need for stable sort, as the chains are guaranteed to be in decreasing
order for the same actor.
---
 chain/messagepool/pruning.go        |  2 +-
 chain/messagepool/selection.go      |  4 ++--
 chain/messagepool/selection_test.go | 37 ++++++++++++++++++++++++++---
 3 files changed, 37 insertions(+), 6 deletions(-)

diff --git a/chain/messagepool/pruning.go b/chain/messagepool/pruning.go
index a4dce3e6d..11719049d 100644
--- a/chain/messagepool/pruning.go
+++ b/chain/messagepool/pruning.go
@@ -44,7 +44,7 @@ func (mp *MessagePool) pruneMessages(ctx context.Context, ts *types.TipSet) erro
 	}
 
 	// Sort the chains
-	sort.SliceStable(chains, func(i, j int) bool {
+	sort.Slice(chains, func(i, j int) bool {
 		return chains[i].Before(chains[j])
 	})
 
diff --git a/chain/messagepool/selection.go b/chain/messagepool/selection.go
index e14efe8d1..38f9477f4 100644
--- a/chain/messagepool/selection.go
+++ b/chain/messagepool/selection.go
@@ -60,7 +60,7 @@ func (mp *MessagePool) selectMessages(curTs, ts *types.TipSet) ([]*types.SignedM
 	}
 
 	// 2. Sort the chains
-	sort.SliceStable(chains, func(i, j int) bool {
+	sort.Slice(chains, func(i, j int) bool {
 		return chains[i].Before(chains[j])
 	})
 
@@ -373,7 +373,7 @@ func (mp *MessagePool) createMessageChains(actor address.Address, mset map[uint6
 		merged := 0
 
 		for i := len(chains) - 1; i > 0; i-- {
-			if chains[i].gasPerf > chains[i-1].gasPerf {
+			if chains[i].gasPerf >= chains[i-1].gasPerf {
 				chains[i-1].msgs = append(chains[i-1].msgs, chains[i].msgs...)
 				chains[i-1].gasReward = new(big.Int).Add(chains[i-1].gasReward, chains[i].gasReward)
 				chains[i-1].gasLimit += chains[i].gasLimit
diff --git a/chain/messagepool/selection_test.go b/chain/messagepool/selection_test.go
index 0bef30d00..bc382bb43 100644
--- a/chain/messagepool/selection_test.go
+++ b/chain/messagepool/selection_test.go
@@ -127,14 +127,45 @@ func TestMessageChains(t *testing.T) {
 		}
 	}
 
-	// test3: 10 messages from a1 to a2, with gasPerf increasing in groups of 3; it should
-	//        make 4 chains, the first 3 with 3 messages and the last with a single message
+	// test3a: 10 messages from a1 to a2, with gasPerf increasing in groups of 3; it should
+	//         merge them in two chains, one with 9 messages and one with the last message
 	mset = make(map[uint64]*types.SignedMessage)
 	for i := 0; i < 10; i++ {
 		m := makeTestMessage(w1, a1, a2, uint64(i), gasLimit, uint64(1+i%3))
 		mset[uint64(i)] = m
 	}
 
+	chains = mp.createMessageChains(a1, mset, ts)
+	if len(chains) != 2 {
+		t.Fatal("expected 1 chain")
+	}
+
+	if len(chains[0].msgs) != 9 {
+		t.Fatalf("expected 9 messages in the chain but got %d", len(chains[0].msgs))
+	}
+	if len(chains[1].msgs) != 1 {
+		t.Fatalf("expected 1 messages in the chain but got %d", len(chains[1].msgs))
+	}
+	nextNonce := 0
+	for _, chain := range chains {
+		for _, m := range chain.msgs {
+			if m.Message.Nonce != uint64(nextNonce) {
+				t.Fatalf("expected nonce %d but got %d", nextNonce, m.Message.Nonce)
+			}
+			nextNonce++
+		}
+	}
+
+	// test3b: 10 messages from a1 to a2, with gasPerf decreasing in groups of 3 with a bias for the
+	//        earlier chains; it should make 4 chains, the first 3 with 3 messages and the last with
+	//        a single message
+	mset = make(map[uint64]*types.SignedMessage)
+	for i := 0; i < 10; i++ {
+		bias := (12 - i) / 3
+		m := makeTestMessage(w1, a1, a2, uint64(i), gasLimit, uint64(1+i%3+bias))
+		mset[uint64(i)] = m
+	}
+
 	chains = mp.createMessageChains(a1, mset, ts)
 	if len(chains) != 4 {
 		t.Fatal("expected 4 chains")
@@ -148,7 +179,7 @@ func TestMessageChains(t *testing.T) {
 			t.Fatalf("expected %d message in chain %d but got %d", expectedLen, i, len(chain.msgs))
 		}
 	}
-	nextNonce := 0
+	nextNonce = 0
 	for _, chain := range chains {
 		for _, m := range chain.msgs {
 			if m.Message.Nonce != uint64(nextNonce) {