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Merge pull request #6932

1cf3dd8 Add unit test for UpdateCoins (Alex Morcos)
03c8282 Make CCoinsViewTest behave like CCoinsViewDB (Alex Morcos)
14470f9 ModifyNewCoins saves database lookups (Alex Morcos)
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laanwj committed Nov 18, 2015
2 parents 03403d8 + 1cf3dd8 commit 73fa5e604356ab4182971376fd758b4680737b5a
Showing with 170 additions and 9 deletions.
  1. +9 −0 src/coins.cpp
  2. +11 −0 src/coins.h
  3. +10 −3 src/main.cpp
  4. +140 −6 src/test/coins_tests.cpp
@@ -117,6 +117,15 @@ CCoinsModifier CCoinsViewCache::ModifyCoins(const uint256 &txid) {
return CCoinsModifier(*this, ret.first, cachedCoinUsage);
}

CCoinsModifier CCoinsViewCache::ModifyNewCoins(const uint256 &txid) {
assert(!hasModifier);
std::pair<CCoinsMap::iterator, bool> ret = cacheCoins.insert(std::make_pair(txid, CCoinsCacheEntry()));
ret.first->second.coins.Clear();
ret.first->second.flags = CCoinsCacheEntry::FRESH;
ret.first->second.flags |= CCoinsCacheEntry::DIRTY;
return CCoinsModifier(*this, ret.first, 0);
}

const CCoins* CCoinsViewCache::AccessCoins(const uint256 &txid) const {
CCoinsMap::const_iterator it = FetchCoins(txid);
if (it == cacheCoins.end()) {
@@ -419,6 +419,17 @@ class CCoinsViewCache : public CCoinsViewBacked
*/
CCoinsModifier ModifyCoins(const uint256 &txid);

/**
* Return a modifiable reference to a CCoins. Assumes that no entry with the given
* txid exists and creates a new one. This saves a database access in the case where
* the coins were to be wiped out by FromTx anyway. This should not be called with
* the 2 historical coinbase duplicate pairs because the new coins are marked fresh, and
* in the event the duplicate coinbase was spent before a flush, the now pruned coins
* would not properly overwrite the first coinbase of the pair. Simultaneous modifications
* are not allowed.
*/
CCoinsModifier ModifyNewCoins(const uint256 &txid);

/**
* Push the modifications applied to this cache to its base.
* Failure to call this method before destruction will cause the changes to be forgotten.
@@ -1310,10 +1310,17 @@ void UpdateCoins(const CTransaction& tx, CValidationState &state, CCoinsViewCach
undo.nVersion = coins->nVersion;
}
}
// add outputs
inputs.ModifyNewCoins(tx.GetHash())->FromTx(tx, nHeight);
}
else {
// add outputs for coinbase tx
// In this case call the full ModifyCoins which will do a database
// lookup to be sure the coins do not already exist otherwise we do not
// know whether to mark them fresh or not. We want the duplicate coinbases
// before BIP30 to still be properly overwritten.
inputs.ModifyCoins(tx.GetHash())->FromTx(tx, nHeight);
}

// add outputs
inputs.ModifyCoins(tx.GetHash())->FromTx(tx, nHeight);
}

void UpdateCoins(const CTransaction& tx, CValidationState &state, CCoinsViewCache &inputs, int nHeight)
@@ -6,6 +6,8 @@
#include "random.h"
#include "uint256.h"
#include "test/test_bitcoin.h"
#include "main.h"
#include "consensus/validation.h"

#include <vector>
#include <map>
@@ -45,15 +47,18 @@ class CCoinsViewTest : public CCoinsView
bool BatchWrite(CCoinsMap& mapCoins, const uint256& hashBlock)
{
for (CCoinsMap::iterator it = mapCoins.begin(); it != mapCoins.end(); ) {
map_[it->first] = it->second.coins;
if (it->second.coins.IsPruned() && insecure_rand() % 3 == 0) {
// Randomly delete empty entries on write.
map_.erase(it->first);
if (it->second.flags & CCoinsCacheEntry::DIRTY) {
// Same optimization used in CCoinsViewDB is to only write dirty entries.
map_[it->first] = it->second.coins;
if (it->second.coins.IsPruned() && insecure_rand() % 3 == 0) {
// Randomly delete empty entries on write.
map_.erase(it->first);
}
}
mapCoins.erase(it++);
}
mapCoins.clear();
hashBestBlock_ = hashBlock;
if (!hashBlock.IsNull())
hashBestBlock_ = hashBlock;
return true;
}

@@ -197,4 +202,133 @@ BOOST_AUTO_TEST_CASE(coins_cache_simulation_test)
BOOST_CHECK(missed_an_entry);
}

// This test is similar to the previous test
// except the emphasis is on testing the functionality of UpdateCoins
// random txs are created and UpdateCoins is used to update the cache stack
// In particular it is tested that spending a duplicate coinbase tx
// has the expected effect (the other duplicate is overwitten at all cache levels)
BOOST_AUTO_TEST_CASE(updatecoins_simulation_test)
{
bool spent_a_duplicate_coinbase = false;
// A simple map to track what we expect the cache stack to represent.
std::map<uint256, CCoins> result;

// The cache stack.
CCoinsViewTest base; // A CCoinsViewTest at the bottom.
std::vector<CCoinsViewCacheTest*> stack; // A stack of CCoinsViewCaches on top.
stack.push_back(new CCoinsViewCacheTest(&base)); // Start with one cache.

// Track the txids we've used and whether they have been spent or not
std::map<uint256, CAmount> coinbaseids;
std::set<uint256> alltxids;
std::set<uint256> duplicateids;

for (unsigned int i = 0; i < NUM_SIMULATION_ITERATIONS; i++) {
{
CMutableTransaction tx;
tx.vin.resize(1);
tx.vout.resize(1);
tx.vout[0].nValue = i; //Keep txs unique unless intended to duplicate
unsigned int height = insecure_rand();

// 1/10 times create a coinbase
if (insecure_rand() % 10 == 0 || coinbaseids.size() < 10) {
// 1/100 times create a duplicate coinbase
if (insecure_rand() % 10 == 0 && coinbaseids.size()) {
std::map<uint256, CAmount>::iterator coinbaseIt = coinbaseids.lower_bound(GetRandHash());
if (coinbaseIt == coinbaseids.end()) {
coinbaseIt = coinbaseids.begin();
}
//Use same random value to have same hash and be a true duplicate
tx.vout[0].nValue = coinbaseIt->second;
assert(tx.GetHash() == coinbaseIt->first);
duplicateids.insert(coinbaseIt->first);
}
else {
coinbaseids[tx.GetHash()] = tx.vout[0].nValue;
}
assert(CTransaction(tx).IsCoinBase());
}
// 9/10 times create a regular tx
else {
uint256 prevouthash;
// equally likely to spend coinbase or non coinbase
std::set<uint256>::iterator txIt = alltxids.lower_bound(GetRandHash());
if (txIt == alltxids.end()) {
txIt = alltxids.begin();
}
prevouthash = *txIt;

// Construct the tx to spend the coins of prevouthash
tx.vin[0].prevout.hash = prevouthash;
tx.vin[0].prevout.n = 0;

// Update the expected result of prevouthash to know these coins are spent
CCoins& oldcoins = result[prevouthash];
oldcoins.Clear();

// It is of particular importance here that once we spend a coinbase tx hash
// it is no longer available to be duplicated (or spent again)
// BIP 34 in conjunction with enforcing BIP 30 (at least until BIP 34 was active)
// results in the fact that no coinbases were duplicated after they were already spent
alltxids.erase(prevouthash);
coinbaseids.erase(prevouthash);

// The test is designed to ensure spending a duplicate coinbase will work properly
// if that ever happens and not resurrect the previously overwritten coinbase
if (duplicateids.count(prevouthash))
spent_a_duplicate_coinbase = true;

assert(!CTransaction(tx).IsCoinBase());
}
// Track this tx to possibly spend later
alltxids.insert(tx.GetHash());

// Update the expected result to know about the new output coins
CCoins &coins = result[tx.GetHash()];
coins.FromTx(tx, height);

CValidationState dummy;
UpdateCoins(tx, dummy, *(stack.back()), height);
}

// Once every 1000 iterations and at the end, verify the full cache.
if (insecure_rand() % 1000 == 1 || i == NUM_SIMULATION_ITERATIONS - 1) {
for (std::map<uint256, CCoins>::iterator it = result.begin(); it != result.end(); it++) {
const CCoins* coins = stack.back()->AccessCoins(it->first);
if (coins) {
BOOST_CHECK(*coins == it->second);
} else {
BOOST_CHECK(it->second.IsPruned());
}
}
}

if (insecure_rand() % 100 == 0) {
// Every 100 iterations, change the cache stack.
if (stack.size() > 0 && insecure_rand() % 2 == 0) {
stack.back()->Flush();
delete stack.back();
stack.pop_back();
}
if (stack.size() == 0 || (stack.size() < 4 && insecure_rand() % 2)) {
CCoinsView* tip = &base;
if (stack.size() > 0) {
tip = stack.back();
}
stack.push_back(new CCoinsViewCacheTest(tip));
}
}
}

// Clean up the stack.
while (stack.size() > 0) {
delete stack.back();
stack.pop_back();
}

// Verify coverage.
BOOST_CHECK(spent_a_duplicate_coinbase);
}

BOOST_AUTO_TEST_SUITE_END()

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