diff options
Diffstat (limited to 'src')
| -rw-r--r-- | src/txmempool.h | 38 | ||||
| -rw-r--r-- | src/validation.cpp | 14 |
2 files changed, 48 insertions, 4 deletions
diff --git a/src/txmempool.h b/src/txmempool.h index fadb554723..9416885125 100644 --- a/src/txmempool.h +++ b/src/txmempool.h @@ -485,7 +485,43 @@ public: > > indexed_transaction_set; - mutable CCriticalSection cs; + /** + * This mutex needs to be locked when accessing `mapTx` or other members + * that are guarded by it. + * + * @par Consistency guarantees + * + * By design, it is guaranteed that: + * + * 1. Locking both `cs_main` and `mempool.cs` will give a view of mempool + * that is consistent with current chain tip (`chainActive` and + * `pcoinsTip`) and is fully populated. Fully populated means that if the + * current active chain is missing transactions that were present in a + * previously active chain, all the missing transactions will have been + * re-added to the mempool and should be present if they meet size and + * consistency constraints. + * + * 2. Locking `mempool.cs` without `cs_main` will give a view of a mempool + * consistent with some chain that was active since `cs_main` was last + * locked, and that is fully populated as described above. It is ok for + * code that only needs to query or remove transactions from the mempool + * to lock just `mempool.cs` without `cs_main`. + * + * To provide these guarantees, it is necessary to lock both `cs_main` and + * `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; diff --git a/src/validation.cpp b/src/validation.cpp index 5696684ed6..25818e496d 100644 --- a/src/validation.cpp +++ b/src/validation.cpp @@ -210,9 +210,17 @@ private: bool RollforwardBlock(const CBlockIndex* pindex, CCoinsViewCache& inputs, const CChainParams& params) EXCLUSIVE_LOCKS_REQUIRED(cs_main); } g_chainstate; - - -CCriticalSection cs_main; +/** + * Mutex to guard access to validation specific variables, such as reading + * or changing the chainstate. + * + * This may also need to be locked when updating the transaction pool, e.g. on + * AcceptToMemoryPool. See CTxMemPool::cs comment for details. + * + * The transaction pool has a separate lock to allow reading from it and the + * chainstate at the same time. + */ +RecursiveMutex cs_main; BlockMap& mapBlockIndex = g_chainstate.mapBlockIndex; CChain& chainActive = g_chainstate.chainActive; |