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Merge #15267: doc: explain AcceptToMemoryPoolWorker's coins_to_uncache

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5d26205272 doc: explain AcceptToMemoryPoolWorker's coins_to_uncache (James O'Beirne)

Pull request description:

  I found ATMPW's `coins_to_uncache` a little hard to understand (see #15264). This adds some doc for posterity.

ACKs for commit 5d2620:
  jnewbery:
    ACK 5d26205272

Tree-SHA512: 088508fa78012fab8680663c4e30f5cee29768416c2ca8b8b2abc29b6ac7067c5a589674f0254474a7ccc95477889d41719760f5796792bf492f51b3dd499c6c
This commit is contained in:
MarcoFalke 2019-04-26 13:09:25 -04:00
commit d76b72a454
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2 changed files with 20 additions and 0 deletions
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4
src/coins.h
View file

@ -294,6 +294,10 @@ public:
bool HaveInputs(const CTransaction& tx) const;
private:
/**
* @note this is marked const, but may actually append to `cacheCoins`, increasing
* memory usage.
*/
CCoinsMap::iterator FetchCoin(const COutPoint &outpoint) const;
};

16
src/validation.cpp
View file

@ -562,6 +562,13 @@ static bool CheckInputsFromMempoolAndCache(const CTransaction& tx, CValidationSt
return CheckInputs(tx, state, view, true, flags, cacheSigStore, true, txdata);
}
/**
* @param[out] coins_to_uncache Return any outpoints which were not previously present in the
* coins cache, but were added as a result of validating the tx
* for mempool acceptance. This allows the caller to optionally
* remove the cache additions if the associated transaction ends
* up being rejected by the mempool.
*/
static bool AcceptToMemoryPoolWorker(const CChainParams& chainparams, CTxMemPool& pool, CValidationState& state, const CTransactionRef& ptx,
bool* pfMissingInputs, int64_t nAcceptTime, std::list<CTransactionRef>* plTxnReplaced,
bool bypass_limits, const CAmount& nAbsurdFee, std::vector<COutPoint>& coins_to_uncache, bool test_accept) EXCLUSIVE_LOCKS_REQUIRED(cs_main)
@ -657,6 +664,10 @@ static bool AcceptToMemoryPoolWorker(const CChainParams& chainparams, CTxMemPool
if (!pcoinsTip->HaveCoinInCache(txin.prevout)) {
coins_to_uncache.push_back(txin.prevout);
}
// Note: this call may add txin.prevout to the coins cache
// (pcoinsTip.cacheCoins) by way of FetchCoin(). It should be removed
// later (via coins_to_uncache) if this tx turns out to be invalid.
if (!view.HaveCoin(txin.prevout)) {
// Are inputs missing because we already have the tx?
for (size_t out = 0; out < tx.vout.size(); out++) {
@ -978,6 +989,11 @@ static bool AcceptToMemoryPoolWithTime(const CChainParams& chainparams, CTxMemPo
std::vector<COutPoint> coins_to_uncache;
bool res = AcceptToMemoryPoolWorker(chainparams, pool, state, tx, pfMissingInputs, nAcceptTime, plTxnReplaced, bypass_limits, nAbsurdFee, coins_to_uncache, test_accept);
if (!res) {
// Remove coins that were not present in the coins cache before calling ATMPW;
// this is to prevent memory DoS in case we receive a large number of
// invalid transactions that attempt to overrun the in-memory coins cache
// (`CCoinsViewCache::cacheCoins`).
for (const COutPoint& hashTx : coins_to_uncache)
pcoinsTip->Uncache(hashTx);
}