From d8541a9f99c58d97ba4908c3a768e518f28d2441 Mon Sep 17 00:00:00 2001
From: Péter Szilágyi <peterke@gmail.com>
Date: Wed, 15 Aug 2018 13:50:16 +0300
Subject: consensus/ethash: use DAGs for remote mining, generate async

---
 consensus/ethash/consensus.go | 50 ++++++++++++++++++++++++++++++++++---------
 1 file changed, 40 insertions(+), 10 deletions(-)

(limited to 'consensus/ethash/consensus.go')

diff --git a/consensus/ethash/consensus.go b/consensus/ethash/consensus.go
index e18a06d52..86fd997ae 100644
--- a/consensus/ethash/consensus.go
+++ b/consensus/ethash/consensus.go
@@ -461,6 +461,13 @@ func calcDifficultyFrontier(time uint64, parent *types.Header) *big.Int {
 // VerifySeal implements consensus.Engine, checking whether the given block satisfies
 // the PoW difficulty requirements.
 func (ethash *Ethash) VerifySeal(chain consensus.ChainReader, header *types.Header) error {
+	return ethash.verifySeal(chain, header, false)
+}
+
+// verifySeal checks whether a block satisfies the PoW difficulty requirements,
+// either using the usual ethash cache for it, or alternatively using a full DAG
+// to make remote mining fast.
+func (ethash *Ethash) verifySeal(chain consensus.ChainReader, header *types.Header, fulldag bool) error {
 	// If we're running a fake PoW, accept any seal as valid
 	if ethash.config.PowMode == ModeFake || ethash.config.PowMode == ModeFullFake {
 		time.Sleep(ethash.fakeDelay)
@@ -471,25 +478,48 @@ func (ethash *Ethash) VerifySeal(chain consensus.ChainReader, header *types.Head
 	}
 	// If we're running a shared PoW, delegate verification to it
 	if ethash.shared != nil {
-		return ethash.shared.VerifySeal(chain, header)
+		return ethash.shared.verifySeal(chain, header, fulldag)
 	}
 	// Ensure that we have a valid difficulty for the block
 	if header.Difficulty.Sign() <= 0 {
 		return errInvalidDifficulty
 	}
-	// Recompute the digest and PoW value and verify against the header
+	// Recompute the digest and PoW values
 	number := header.Number.Uint64()
 
-	cache := ethash.cache(number)
-	size := datasetSize(number)
-	if ethash.config.PowMode == ModeTest {
-		size = 32 * 1024
+	var (
+		digest []byte
+		result []byte
+	)
+	// If fast-but-heavy PoW verification was requested, use an ethash dataset
+	if fulldag {
+		dataset := ethash.dataset(number, true)
+		if dataset.generated() {
+			digest, result = hashimotoFull(dataset.dataset, header.HashNoNonce().Bytes(), header.Nonce.Uint64())
+
+			// Datasets are unmapped in a finalizer. Ensure that the dataset stays alive
+			// until after the call to hashimotoFull so it's not unmapped while being used.
+			runtime.KeepAlive(dataset)
+		} else {
+			// Dataset not yet generated, don't hang, use a cache instead
+			fulldag = false
+		}
 	}
-	digest, result := hashimotoLight(size, cache.cache, header.HashNoNonce().Bytes(), header.Nonce.Uint64())
-	// Caches are unmapped in a finalizer. Ensure that the cache stays live
-	// until after the call to hashimotoLight so it's not unmapped while being used.
-	runtime.KeepAlive(cache)
+	// If slow-but-light PoW verification was requested (or DAG not yet ready), use an ethash cache
+	if !fulldag {
+		cache := ethash.cache(number)
+
+		size := datasetSize(number)
+		if ethash.config.PowMode == ModeTest {
+			size = 32 * 1024
+		}
+		digest, result = hashimotoLight(size, cache.cache, header.HashNoNonce().Bytes(), header.Nonce.Uint64())
 
+		// Caches are unmapped in a finalizer. Ensure that the cache stays alive
+		// until after the call to hashimotoLight so it's not unmapped while being used.
+		runtime.KeepAlive(cache)
+	}
+	// Verify the calculated values against the ones provided in the header
 	if !bytes.Equal(header.MixDigest[:], digest) {
 		return errInvalidMixDigest
 	}
-- 
cgit