diff options
Diffstat (limited to 'src')
-rw-r--r-- | src/rpc/mining.cpp | 3 | ||||
-rw-r--r-- | src/test/validation_block_tests.cpp | 152 | ||||
-rw-r--r-- | src/txmempool.cpp | 20 | ||||
-rw-r--r-- | src/txmempool.h | 36 | ||||
-rw-r--r-- | src/validation.cpp | 10 | ||||
-rw-r--r-- | src/validation.h | 7 |
6 files changed, 183 insertions, 45 deletions
diff --git a/src/rpc/mining.cpp b/src/rpc/mining.cpp index 477f05f46c..86b0845738 100644 --- a/src/rpc/mining.cpp +++ b/src/rpc/mining.cpp @@ -469,7 +469,7 @@ static UniValue getblocktemplate(const JSONRPCRequest& request) nTransactionsUpdatedLastLP = nTransactionsUpdatedLast; } - // Release the wallet and main lock while waiting + // Release lock while waiting LEAVE_CRITICAL_SECTION(cs_main); { checktxtime = std::chrono::steady_clock::now() + std::chrono::minutes(1); @@ -480,6 +480,7 @@ static UniValue getblocktemplate(const JSONRPCRequest& request) if (g_best_block_cv.wait_until(lock, checktxtime) == std::cv_status::timeout) { // Timeout: Check transactions for update + // without holding ::mempool.cs to avoid deadlocks if (mempool.GetTransactionsUpdated() != nTransactionsUpdatedLastLP) break; checktxtime += std::chrono::seconds(10); diff --git a/src/test/validation_block_tests.cpp b/src/test/validation_block_tests.cpp index 6a9813442b..b3368d44b6 100644 --- a/src/test/validation_block_tests.cpp +++ b/src/test/validation_block_tests.cpp @@ -10,6 +10,7 @@ #include <miner.h> #include <pow.h> #include <random.h> +#include <script/standard.h> #include <test/setup_common.h> #include <util/time.h> #include <validation.h> @@ -21,6 +22,8 @@ struct RegtestingSetup : public TestingSetup { RegtestingSetup() : TestingSetup(CBaseChainParams::REGTEST) {} }; +static const std::vector<unsigned char> V_OP_TRUE{OP_TRUE}; + BOOST_FIXTURE_TEST_SUITE(validation_block_tests, RegtestingSetup) struct TestSubscriber : public CValidationInterface { @@ -62,8 +65,21 @@ std::shared_ptr<CBlock> Block(const uint256& prev_hash) pblock->hashPrevBlock = prev_hash; pblock->nTime = ++time; + pubKey.clear(); + { + WitnessV0ScriptHash witness_program; + CSHA256().Write(&V_OP_TRUE[0], V_OP_TRUE.size()).Finalize(witness_program.begin()); + pubKey << OP_0 << ToByteVector(witness_program); + } + + // Make the coinbase transaction with two outputs: + // One zero-value one that has a unique pubkey to make sure that blocks at the same height can have a different hash + // Another one that has the coinbase reward in a P2WSH with OP_TRUE as witness program to make it easy to spend CMutableTransaction txCoinbase(*pblock->vtx[0]); - txCoinbase.vout.resize(1); + txCoinbase.vout.resize(2); + txCoinbase.vout[1].scriptPubKey = pubKey; + txCoinbase.vout[1].nValue = txCoinbase.vout[0].nValue; + txCoinbase.vout[0].nValue = 0; txCoinbase.vin[0].scriptWitness.SetNull(); pblock->vtx[0] = MakeTransactionRef(std::move(txCoinbase)); @@ -72,6 +88,9 @@ std::shared_ptr<CBlock> Block(const uint256& prev_hash) std::shared_ptr<CBlock> FinalizeBlock(std::shared_ptr<CBlock> pblock) { + LOCK(cs_main); // For LookupBlockIndex + GenerateCoinbaseCommitment(*pblock, LookupBlockIndex(pblock->hashPrevBlock), Params().GetConsensus()); + pblock->hashMerkleRoot = BlockMerkleRoot(*pblock); while (!CheckProofOfWork(pblock->GetHash(), pblock->nBits, Params().GetConsensus())) { @@ -82,13 +101,13 @@ std::shared_ptr<CBlock> FinalizeBlock(std::shared_ptr<CBlock> pblock) } // construct a valid block -const std::shared_ptr<const CBlock> GoodBlock(const uint256& prev_hash) +std::shared_ptr<const CBlock> GoodBlock(const uint256& prev_hash) { return FinalizeBlock(Block(prev_hash)); } // construct an invalid block (but with a valid header) -const std::shared_ptr<const CBlock> BadBlock(const uint256& prev_hash) +std::shared_ptr<const CBlock> BadBlock(const uint256& prev_hash) { auto pblock = Block(prev_hash); @@ -188,4 +207,131 @@ BOOST_AUTO_TEST_CASE(processnewblock_signals_ordering) BOOST_CHECK_EQUAL(sub.m_expected_tip, ::ChainActive().Tip()->GetBlockHash()); } +/** + * Test that mempool updates happen atomically with reorgs. + * + * This prevents RPC clients, among others, from retrieving immediately-out-of-date mempool data + * during large reorgs. + * + * The test verifies this by creating a chain of `num_txs` blocks, matures their coinbases, and then + * submits txns spending from their coinbase to the mempool. A fork chain is then processed, + * invalidating the txns and evicting them from the mempool. + * + * We verify that the mempool updates atomically by polling it continuously + * from another thread during the reorg and checking that its size only changes + * once. The size changing exactly once indicates that the polling thread's + * view of the mempool is either consistent with the chain state before reorg, + * or consistent with the chain state after the reorg, and not just consistent + * with some intermediate state during the reorg. + */ +BOOST_AUTO_TEST_CASE(mempool_locks_reorg) +{ + bool ignored; + auto ProcessBlock = [&ignored](std::shared_ptr<const CBlock> block) -> bool { + return ProcessNewBlock(Params(), block, /* fForceProcessing */ true, /* fNewBlock */ &ignored); + }; + + // Process all mined blocks + BOOST_REQUIRE(ProcessBlock(std::make_shared<CBlock>(Params().GenesisBlock()))); + auto last_mined = GoodBlock(Params().GenesisBlock().GetHash()); + BOOST_REQUIRE(ProcessBlock(last_mined)); + + // Run the test multiple times + for (int test_runs = 3; test_runs > 0; --test_runs) { + BOOST_CHECK_EQUAL(last_mined->GetHash(), ::ChainActive().Tip()->GetBlockHash()); + + // Later on split from here + const uint256 split_hash{last_mined->hashPrevBlock}; + + // Create a bunch of transactions to spend the miner rewards of the + // most recent blocks + std::vector<CTransactionRef> txs; + for (int num_txs = 22; num_txs > 0; --num_txs) { + CMutableTransaction mtx; + mtx.vin.push_back(CTxIn{COutPoint{last_mined->vtx[0]->GetHash(), 1}, CScript{}}); + mtx.vin[0].scriptWitness.stack.push_back(V_OP_TRUE); + mtx.vout.push_back(last_mined->vtx[0]->vout[1]); + mtx.vout[0].nValue -= 1000; + txs.push_back(MakeTransactionRef(mtx)); + + last_mined = GoodBlock(last_mined->GetHash()); + BOOST_REQUIRE(ProcessBlock(last_mined)); + } + + // Mature the inputs of the txs + for (int j = COINBASE_MATURITY; j > 0; --j) { + last_mined = GoodBlock(last_mined->GetHash()); + BOOST_REQUIRE(ProcessBlock(last_mined)); + } + + // Mine a reorg (and hold it back) before adding the txs to the mempool + const uint256 tip_init{last_mined->GetHash()}; + + std::vector<std::shared_ptr<const CBlock>> reorg; + last_mined = GoodBlock(split_hash); + reorg.push_back(last_mined); + for (size_t j = COINBASE_MATURITY + txs.size() + 1; j > 0; --j) { + last_mined = GoodBlock(last_mined->GetHash()); + reorg.push_back(last_mined); + } + + // Add the txs to the tx pool + { + LOCK(cs_main); + CValidationState state; + std::list<CTransactionRef> plTxnReplaced; + for (const auto& tx : txs) { + BOOST_REQUIRE(AcceptToMemoryPool( + ::mempool, + state, + tx, + /* pfMissingInputs */ &ignored, + &plTxnReplaced, + /* bypass_limits */ false, + /* nAbsurdFee */ 0)); + } + } + + // Check that all txs are in the pool + { + LOCK(::mempool.cs); + BOOST_CHECK_EQUAL(::mempool.mapTx.size(), txs.size()); + } + + // Run a thread that simulates an RPC caller that is polling while + // validation is doing a reorg + std::thread rpc_thread{[&]() { + // This thread is checking that the mempool either contains all of + // the transactions invalidated by the reorg, or none of them, and + // not some intermediate amount. + while (true) { + LOCK(::mempool.cs); + if (::mempool.mapTx.size() == 0) { + // We are done with the reorg + break; + } + // Internally, we might be in the middle of the reorg, but + // externally the reorg to the most-proof-of-work chain should + // be atomic. So the caller assumes that the returned mempool + // is consistent. That is, it has all txs that were there + // before the reorg. + assert(::mempool.mapTx.size() == txs.size()); + continue; + } + LOCK(cs_main); + // We are done with the reorg, so the tip must have changed + assert(tip_init != ::ChainActive().Tip()->GetBlockHash()); + }}; + + // Submit the reorg in this thread to invalidate and remove the txs from the tx pool + for (const auto& b : reorg) { + ProcessBlock(b); + } + // Check that the reorg was eventually successful + BOOST_CHECK_EQUAL(last_mined->GetHash(), ::ChainActive().Tip()->GetBlockHash()); + + // We can join the other thread, which returns when the reorg was successful + rpc_thread.join(); + } +} BOOST_AUTO_TEST_SUITE_END() diff --git a/src/txmempool.cpp b/src/txmempool.cpp index cac7beb6a1..9257cff718 100644 --- a/src/txmempool.cpp +++ b/src/txmempool.cpp @@ -104,7 +104,7 @@ void CTxMemPool::UpdateForDescendants(txiter updateIt, cacheMap &cachedDescendan // for each such descendant, also update the ancestor state to include the parent. void CTxMemPool::UpdateTransactionsFromBlock(const std::vector<uint256> &vHashesToUpdate) { - LOCK(cs); + AssertLockHeld(cs); // For each entry in vHashesToUpdate, store the set of in-mempool, but not // in-vHashesToUpdate transactions, so that we don't have to recalculate // descendants when we come across a previously seen entry. @@ -322,8 +322,8 @@ void CTxMemPoolEntry::UpdateAncestorState(int64_t modifySize, CAmount modifyFee, assert(int(nSigOpCostWithAncestors) >= 0); } -CTxMemPool::CTxMemPool(CBlockPolicyEstimator* estimator) : - nTransactionsUpdated(0), minerPolicyEstimator(estimator) +CTxMemPool::CTxMemPool(CBlockPolicyEstimator* estimator) + : nTransactionsUpdated(0), minerPolicyEstimator(estimator) { _clear(); //lock free clear @@ -341,13 +341,11 @@ bool CTxMemPool::isSpent(const COutPoint& outpoint) const unsigned int CTxMemPool::GetTransactionsUpdated() const { - LOCK(cs); return nTransactionsUpdated; } void CTxMemPool::AddTransactionsUpdated(unsigned int n) { - LOCK(cs); nTransactionsUpdated += n; } @@ -459,8 +457,7 @@ void CTxMemPool::CalculateDescendants(txiter entryit, setEntries& setDescendants void CTxMemPool::removeRecursive(const CTransaction &origTx, MemPoolRemovalReason reason) { // Remove transaction from memory pool - { - LOCK(cs); + AssertLockHeld(cs); setEntries txToRemove; txiter origit = mapTx.find(origTx.GetHash()); if (origit != mapTx.end()) { @@ -485,13 +482,12 @@ void CTxMemPool::removeRecursive(const CTransaction &origTx, MemPoolRemovalReaso } RemoveStaged(setAllRemoves, false, reason); - } } void CTxMemPool::removeForReorg(const CCoinsViewCache *pcoins, unsigned int nMemPoolHeight, int flags) { // Remove transactions spending a coinbase which are now immature and no-longer-final transactions - LOCK(cs); + AssertLockHeld(cs); setEntries txToRemove; for (indexed_transaction_set::const_iterator it = mapTx.begin(); it != mapTx.end(); it++) { const CTransaction& tx = it->GetTx(); @@ -547,7 +543,7 @@ void CTxMemPool::removeConflicts(const CTransaction &tx) */ void CTxMemPool::removeForBlock(const std::vector<CTransactionRef>& vtx, unsigned int nBlockHeight) { - LOCK(cs); + AssertLockHeld(cs); std::vector<const CTxMemPoolEntry*> entries; for (const auto& tx : vtx) { @@ -922,7 +918,7 @@ void CTxMemPool::RemoveStaged(setEntries &stage, bool updateDescendants, MemPool } int CTxMemPool::Expire(int64_t time) { - LOCK(cs); + AssertLockHeld(cs); indexed_transaction_set::index<entry_time>::type::iterator it = mapTx.get<entry_time>().begin(); setEntries toremove; while (it != mapTx.get<entry_time>().end() && it->GetTime() < time) { @@ -1015,7 +1011,7 @@ void CTxMemPool::trackPackageRemoved(const CFeeRate& rate) { } void CTxMemPool::TrimToSize(size_t sizelimit, std::vector<COutPoint>* pvNoSpendsRemaining) { - LOCK(cs); + AssertLockHeld(cs); unsigned nTxnRemoved = 0; CFeeRate maxFeeRateRemoved(0); diff --git a/src/txmempool.h b/src/txmempool.h index ce0b762336..565dd61f0f 100644 --- a/src/txmempool.h +++ b/src/txmempool.h @@ -6,12 +6,13 @@ #ifndef BITCOIN_TXMEMPOOL_H #define BITCOIN_TXMEMPOOL_H +#include <atomic> +#include <map> #include <memory> #include <set> -#include <map> -#include <vector> -#include <utility> #include <string> +#include <utility> +#include <vector> #include <amount.h> #include <coins.h> @@ -443,7 +444,7 @@ class CTxMemPool { private: uint32_t nCheckFrequency GUARDED_BY(cs); //!< Value n means that n times in 2^32 we check. - unsigned int nTransactionsUpdated; //!< Used by getblocktemplate to trigger CreateNewBlock() invocation + std::atomic<unsigned int> nTransactionsUpdated; //!< Used by getblocktemplate to trigger CreateNewBlock() invocation CBlockPolicyEstimator* minerPolicyEstimator; uint64_t totalTxSize; //!< sum of all mempool tx's virtual sizes. Differs from serialized tx size since witness data is discounted. Defined in BIP 141. @@ -513,21 +514,12 @@ public: * `mempool.cs` whenever adding transactions to the mempool and whenever * changing the chain tip. It's necessary to keep both mutexes locked until * the mempool is consistent with the new chain tip and fully populated. - * - * @par Consistency bug - * - * The second guarantee above is not currently enforced, but - * https://github.com/bitcoin/bitcoin/pull/14193 will fix it. No known code - * in bitcoin currently depends on second guarantee, but it is important to - * fix for third party code that needs be able to frequently poll the - * mempool without locking `cs_main` and without encountering missing - * transactions during reorgs. */ mutable RecursiveMutex cs; indexed_transaction_set mapTx GUARDED_BY(cs); using txiter = indexed_transaction_set::nth_index<0>::type::const_iterator; - std::vector<std::pair<uint256, txiter> > vTxHashes; //!< All tx witness hashes/entries in mapTx, in random order + std::vector<std::pair<uint256, txiter>> vTxHashes GUARDED_BY(cs); //!< All tx witness hashes/entries in mapTx, in random order struct CompareIteratorByHash { bool operator()(const txiter &a, const txiter &b) const { @@ -582,10 +574,10 @@ public: void addUnchecked(const CTxMemPoolEntry& entry, bool validFeeEstimate = true) EXCLUSIVE_LOCKS_REQUIRED(cs, cs_main); void addUnchecked(const CTxMemPoolEntry& entry, setEntries& setAncestors, bool validFeeEstimate = true) EXCLUSIVE_LOCKS_REQUIRED(cs, cs_main); - void removeRecursive(const CTransaction &tx, MemPoolRemovalReason reason = MemPoolRemovalReason::UNKNOWN); - void removeForReorg(const CCoinsViewCache *pcoins, unsigned int nMemPoolHeight, int flags) EXCLUSIVE_LOCKS_REQUIRED(cs_main); - void removeConflicts(const CTransaction &tx) EXCLUSIVE_LOCKS_REQUIRED(cs); - void removeForBlock(const std::vector<CTransactionRef>& vtx, unsigned int nBlockHeight); + void removeRecursive(const CTransaction& tx, MemPoolRemovalReason reason = MemPoolRemovalReason::UNKNOWN) EXCLUSIVE_LOCKS_REQUIRED(cs); + void removeForReorg(const CCoinsViewCache* pcoins, unsigned int nMemPoolHeight, int flags) EXCLUSIVE_LOCKS_REQUIRED(cs, cs_main); + void removeConflicts(const CTransaction& tx) EXCLUSIVE_LOCKS_REQUIRED(cs); + void removeForBlock(const std::vector<CTransactionRef>& vtx, unsigned int nBlockHeight) EXCLUSIVE_LOCKS_REQUIRED(cs); void clear(); void _clear() EXCLUSIVE_LOCKS_REQUIRED(cs); //lock free @@ -598,7 +590,7 @@ public: * Check that none of this transactions inputs are in the mempool, and thus * the tx is not dependent on other mempool transactions to be included in a block. */ - bool HasNoInputsOf(const CTransaction& tx) const; + bool HasNoInputsOf(const CTransaction& tx) const EXCLUSIVE_LOCKS_REQUIRED(cs); /** Affect CreateNewBlock prioritisation of transactions */ void PrioritiseTransaction(const uint256& hash, const CAmount& nFeeDelta); @@ -632,7 +624,7 @@ public: * for). Note: vHashesToUpdate should be the set of transactions from the * disconnected block that have been accepted back into the mempool. */ - void UpdateTransactionsFromBlock(const std::vector<uint256>& vHashesToUpdate) EXCLUSIVE_LOCKS_REQUIRED(cs_main); + void UpdateTransactionsFromBlock(const std::vector<uint256>& vHashesToUpdate) EXCLUSIVE_LOCKS_REQUIRED(cs, cs_main); /** Try to calculate all in-mempool ancestors of entry. * (these are all calculated including the tx itself) @@ -663,10 +655,10 @@ public: * pvNoSpendsRemaining, if set, will be populated with the list of outpoints * which are not in mempool which no longer have any spends in this mempool. */ - void TrimToSize(size_t sizelimit, std::vector<COutPoint>* pvNoSpendsRemaining=nullptr); + void TrimToSize(size_t sizelimit, std::vector<COutPoint>* pvNoSpendsRemaining = nullptr) EXCLUSIVE_LOCKS_REQUIRED(cs); /** Expire all transaction (and their dependencies) in the mempool older than time. Return the number of removed transactions. */ - int Expire(int64_t time); + int Expire(int64_t time) EXCLUSIVE_LOCKS_REQUIRED(cs); /** * Calculate the ancestor and descendant count for the given transaction. diff --git a/src/validation.cpp b/src/validation.cpp index d39b78614c..c6995ed24b 100644 --- a/src/validation.cpp +++ b/src/validation.cpp @@ -304,7 +304,8 @@ bool CheckSequenceLocks(const CTxMemPool& pool, const CTransaction& tx, int flag // Returns the script flags which should be checked for a given block static unsigned int GetBlockScriptFlags(const CBlockIndex* pindex, const Consensus::Params& chainparams); -static void LimitMempoolSize(CTxMemPool& pool, size_t limit, unsigned long age) { +static void LimitMempoolSize(CTxMemPool& pool, size_t limit, unsigned long age) EXCLUSIVE_LOCKS_REQUIRED(pool.cs) +{ int expired = pool.Expire(GetTime() - age); if (expired != 0) { LogPrint(BCLog::MEMPOOL, "Expired %i transactions from the memory pool\n", expired); @@ -341,7 +342,7 @@ static bool IsCurrentForFeeEstimation() EXCLUSIVE_LOCKS_REQUIRED(cs_main) * and instead just erase from the mempool as needed. */ -static void UpdateMempoolForReorg(DisconnectedBlockTransactions &disconnectpool, bool fAddToMempool) EXCLUSIVE_LOCKS_REQUIRED(cs_main) +static void UpdateMempoolForReorg(DisconnectedBlockTransactions& disconnectpool, bool fAddToMempool) EXCLUSIVE_LOCKS_REQUIRED(cs_main, ::mempool.cs) { AssertLockHeld(cs_main); std::vector<uint256> vHashUpdate; @@ -2547,7 +2548,7 @@ bool CChainState::ActivateBestChain(CValidationState &state, const CChainParams& LimitValidationInterfaceQueue(); { - LOCK(cs_main); + LOCK2(cs_main, ::mempool.cs); // Lock transaction pool for at least as long as it takes for connectTrace to be consumed CBlockIndex* starting_tip = m_chain.Tip(); bool blocks_connected = false; do { @@ -2667,6 +2668,7 @@ bool CChainState::InvalidateBlock(CValidationState& state, const CChainParams& c LimitValidationInterfaceQueue(); LOCK(cs_main); + LOCK(::mempool.cs); // Lock for as long as disconnectpool is in scope to make sure UpdateMempoolForReorg is called after DisconnectTip without unlocking in between if (!m_chain.Contains(pindex)) break; pindex_was_in_chain = true; CBlockIndex *invalid_walk_tip = m_chain.Tip(); @@ -4100,7 +4102,7 @@ bool CChainState::RewindBlockIndex(const CChainParams& params) // Loop until the tip is below nHeight, or we reach a pruned block. while (!ShutdownRequested()) { { - LOCK(cs_main); + LOCK2(cs_main, ::mempool.cs); // Make sure nothing changed from under us (this won't happen because RewindBlockIndex runs before importing/network are active) assert(tip == m_chain.Tip()); if (tip == nullptr || tip->nHeight < nHeight) break; diff --git a/src/validation.h b/src/validation.h index 638229952d..9573d62048 100644 --- a/src/validation.h +++ b/src/validation.h @@ -18,6 +18,7 @@ #include <protocol.h> // For CMessageHeader::MessageStartChars #include <script/script_error.h> #include <sync.h> +#include <txmempool.h> // For CTxMemPool::cs #include <versionbits.h> #include <algorithm> @@ -553,7 +554,7 @@ public: CCoinsViewCache& view, const CChainParams& chainparams, bool fJustCheck = false) EXCLUSIVE_LOCKS_REQUIRED(cs_main); // Block disconnection on our pcoinsTip: - bool DisconnectTip(CValidationState& state, const CChainParams& chainparams, DisconnectedBlockTransactions* disconnectpool) EXCLUSIVE_LOCKS_REQUIRED(cs_main); + bool DisconnectTip(CValidationState& state, const CChainParams& chainparams, DisconnectedBlockTransactions* disconnectpool) EXCLUSIVE_LOCKS_REQUIRED(cs_main, ::mempool.cs); // Manual block validity manipulation: bool PreciousBlock(CValidationState& state, const CChainParams& params, CBlockIndex* pindex) LOCKS_EXCLUDED(cs_main); @@ -572,8 +573,8 @@ public: bool IsInitialBlockDownload() const; private: - bool ActivateBestChainStep(CValidationState& state, const CChainParams& chainparams, CBlockIndex* pindexMostWork, const std::shared_ptr<const CBlock>& pblock, bool& fInvalidFound, ConnectTrace& connectTrace) EXCLUSIVE_LOCKS_REQUIRED(cs_main); - bool ConnectTip(CValidationState& state, const CChainParams& chainparams, CBlockIndex* pindexNew, const std::shared_ptr<const CBlock>& pblock, ConnectTrace& connectTrace, DisconnectedBlockTransactions &disconnectpool) EXCLUSIVE_LOCKS_REQUIRED(cs_main); + bool ActivateBestChainStep(CValidationState& state, const CChainParams& chainparams, CBlockIndex* pindexMostWork, const std::shared_ptr<const CBlock>& pblock, bool& fInvalidFound, ConnectTrace& connectTrace) EXCLUSIVE_LOCKS_REQUIRED(cs_main, ::mempool.cs); + bool ConnectTip(CValidationState& state, const CChainParams& chainparams, CBlockIndex* pindexNew, const std::shared_ptr<const CBlock>& pblock, ConnectTrace& connectTrace, DisconnectedBlockTransactions& disconnectpool) EXCLUSIVE_LOCKS_REQUIRED(cs_main, ::mempool.cs); CBlockIndex* AddToBlockIndex(const CBlockHeader& block) EXCLUSIVE_LOCKS_REQUIRED(cs_main); /** Create a new block index entry for a given block hash */ |