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

@@ -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])
 	})
 

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

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
+	// test3a: 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
+	//         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) {