Use ModifyCoins instead of mutable GetCoins.

Replace the mutable non-copying GetCoins method with a ModifyCoins, which
returns an encapsulated iterator, so we can keep track of concurrent
modifications (as iterators can be invalidated by those) and run cleanup
code after a modification is finished.

This also removes the overloading of the 'GetCoins' name.

src/bitcoin-tx.cpp

@@ -384,21 +384,19 @@ static void MutateTxSign(CMutableTransaction& tx, const string& flagStr)
             vector<unsigned char> pkData(ParseHexUV(prevOut, "scriptPubKey"));
             CScript scriptPubKey(pkData.begin(), pkData.end());
 
-            CCoins coins;
-            if (view.GetCoins(txid, coins)) {
-                if (coins.IsAvailable(nOut) && coins.vout[nOut].scriptPubKey != scriptPubKey) {
+            {
+                CCoinsModifier coins = view.ModifyCoins(txid);
+                if (coins->IsAvailable(nOut) && coins->vout[nOut].scriptPubKey != scriptPubKey) {
                     string err("Previous output scriptPubKey mismatch:\n");
-                    err = err + coins.vout[nOut].scriptPubKey.ToString() + "\nvs:\n"+
+                    err = err + coins->vout[nOut].scriptPubKey.ToString() + "\nvs:\n"+
                         scriptPubKey.ToString();
                     throw runtime_error(err);
                 }
-                // what todo if txid is known, but the actual output isn't?
+                if ((unsigned int)nOut >= coins->vout.size())
+                    coins->vout.resize(nOut+1);
+                coins->vout[nOut].scriptPubKey = scriptPubKey;
+                coins->vout[nOut].nValue = 0; // we don't know the actual output value
             }
-            if ((unsigned int)nOut >= coins.vout.size())
-                coins.vout.resize(nOut+1);
-            coins.vout[nOut].scriptPubKey = scriptPubKey;
-            coins.vout[nOut].nValue = 0; // we don't know the actual output value
-            view.SetCoins(txid, coins);
 
             // if redeemScript given and private keys given,
             // add redeemScript to the tempKeystore so it can be signed:

src/coins.cpp

@@ -73,7 +73,7 @@ bool CCoinsViewBacked::GetStats(CCoinsStats &stats) const { return base->GetStat
 
 CCoinsKeyHasher::CCoinsKeyHasher() : salt(GetRandHash()) {}
 
-CCoinsViewCache::CCoinsViewCache(CCoinsView &baseIn, bool fDummy) : CCoinsViewBacked(baseIn), hashBlock(0) { }
+CCoinsViewCache::CCoinsViewCache(CCoinsView &baseIn, bool fDummy) : CCoinsViewBacked(baseIn), hasModifier(false), hashBlock(0) { }
 
 bool CCoinsViewCache::GetCoins(const uint256 &txid, CCoins &coins) const {
     if (cacheCoins.count(txid)) {
@@ -87,7 +87,12 @@ bool CCoinsViewCache::GetCoins(const uint256 &txid, CCoins &coins) const {
     return false;
 }
 
-CCoinsMap::iterator CCoinsViewCache::FetchCoins(const uint256 &txid) {
+CCoinsViewCache::~CCoinsViewCache()
+{
+    assert(!hasModifier);
+}
+
+CCoinsMap::const_iterator CCoinsViewCache::FetchCoins(const uint256 &txid) const {
     CCoinsMap::iterator it = cacheCoins.find(txid);
     if (it != cacheCoins.end())
         return it;
@@ -99,15 +104,15 @@ CCoinsMap::iterator CCoinsViewCache::FetchCoins(const uint256 &txid) {
     return ret;
 }
 
-CCoinsMap::const_iterator CCoinsViewCache::FetchCoins(const uint256 &txid) const {
-    /* Avoid redundant implementation with the const-cast.  */
-    return const_cast<CCoinsViewCache*>(this)->FetchCoins(txid);
-}
-
-CCoins &CCoinsViewCache::GetCoins(const uint256 &txid) {
-    CCoinsMap::iterator it = FetchCoins(txid);
-    assert(it != cacheCoins.end());
-    return it->second;
+CCoinsModifier CCoinsViewCache::ModifyCoins(const uint256 &txid) {
+    assert(!hasModifier);
+    hasModifier = true;
+    std::pair<CCoinsMap::iterator, bool> ret = cacheCoins.insert(std::make_pair(txid, CCoins()));
+    if (ret.second) {
+        if (!base->GetCoins(txid, ret.first->second))
+            ret.first->second.Clear();
+    }
+    return CCoinsModifier(*this, ret.first);
 }
 
 const CCoins* CCoinsViewCache::AccessCoins(const uint256 &txid) const {
@@ -145,6 +150,7 @@ bool CCoinsViewCache::SetBestBlock(const uint256 &hashBlockIn) {
 }
 
 bool CCoinsViewCache::BatchWrite(CCoinsMap &mapCoins, const uint256 &hashBlockIn) {
+    assert(!hasModifier);
     for (CCoinsMap::iterator it = mapCoins.begin(); it != mapCoins.end();) {
         cacheCoins[it->first].swap(it->second);
         CCoinsMap::iterator itOld = it++;
@@ -213,3 +219,11 @@ double CCoinsViewCache::GetPriority(const CTransaction &tx, int nHeight) const
     }
     return tx.ComputePriority(dResult);
 }
+
+CCoinsModifier::CCoinsModifier(CCoinsViewCache& cache_, CCoinsMap::iterator it_) : cache(cache_), it(it_) {}
+
+CCoinsModifier::~CCoinsModifier() {
+    assert(cache.hasModifier);
+    cache.hasModifier = false;
+    it->second.Cleanup();
+}

src/coins.h

@@ -83,11 +83,26 @@ public:
     // as new tx version will probably only be introduced at certain heights
     int nVersion;
 
-    // construct a CCoins from a CTransaction, at a given height
-    CCoins(const CTransaction &tx, int nHeightIn) : fCoinBase(tx.IsCoinBase()), vout(tx.vout), nHeight(nHeightIn), nVersion(tx.nVersion) {
+    void FromTx(const CTransaction &tx, int nHeightIn) {
+        fCoinBase = tx.IsCoinBase();
+        vout = tx.vout;
+        nHeight = nHeightIn;
+        nVersion = tx.nVersion;
         ClearUnspendable();
     }
 
+    // construct a CCoins from a CTransaction, at a given height
+    CCoins(const CTransaction &tx, int nHeightIn) {
+        FromTx(tx, nHeightIn);
+    }
+
+    void Clear() {
+        fCoinBase = false;
+        std::vector<CTxOut>().swap(vout);
+        nHeight = 0;
+        nVersion = 0;
+    }
+
     // empty constructor
     CCoins() : fCoinBase(false), vout(0), nHeight(0), nVersion(0) { }
 
@@ -323,10 +338,31 @@ public:
 };
 
 
+class CCoinsViewCache;
+
+/** A reference to a mutable cache entry. Encapsulating it allows us to run
+ *  cleanup code after the modification is finished, and keeping track of
+ *  concurrent modifications. */
+class CCoinsModifier
+{
+private:
+    CCoinsViewCache& cache;
+    CCoinsMap::iterator it;
+    CCoinsModifier(CCoinsViewCache& cache_, CCoinsMap::iterator it_);
+
+public:
+    CCoins* operator->() { return &it->second; }
+    CCoins& operator*() { return it->second; }
+    ~CCoinsModifier();
+    friend class CCoinsViewCache;
+};
+
 /** CCoinsView that adds a memory cache for transactions to another CCoinsView */
 class CCoinsViewCache : public CCoinsViewBacked
 {
 protected:
+    /* Whether this cache has an active modifier. */
+    bool hasModifier;
 
     /* Make mutable so that we can "fill the cache" even from Get-methods
        declared as "const".  */
@@ -335,6 +371,7 @@ protected:
 
 public:
     CCoinsViewCache(CCoinsView &baseIn, bool fDummy = false);
+    ~CCoinsViewCache();
 
     // Standard CCoinsView methods
     bool GetCoins(const uint256 &txid, CCoins &coins) const;
@@ -349,8 +386,10 @@ public:
     // allowed while accessing the returned pointer.
     const CCoins* AccessCoins(const uint256 &txid) const;
 
-    // Return a modifiable reference to a CCoins. Check HaveCoins first.
-    CCoins &GetCoins(const uint256 &txid);
+    // Return a modifiable reference to a CCoins. If no entry with the given
+    // txid exists, a new one is created. Simultaneous modifications are not
+    // allowed.
+    CCoinsModifier ModifyCoins(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.
@@ -377,6 +416,8 @@ public:
 
     const CTxOut &GetOutputFor(const CTxIn& input) const;
 
+    friend class CCoinsModifier;
+
 private:
     CCoinsMap::iterator FetchCoins(const uint256 &txid);
     CCoinsMap::const_iterator FetchCoins(const uint256 &txid) const;

src/main.cpp

@@ -1348,22 +1348,18 @@ void static InvalidBlockFound(CBlockIndex *pindex, const CValidationState &state
 
 void UpdateCoins(const CTransaction& tx, CValidationState &state, CCoinsViewCache &inputs, CTxUndo &txundo, int nHeight)
 {
-    bool ret;
     // mark inputs spent
     if (!tx.IsCoinBase()) {
         txundo.vprevout.reserve(tx.vin.size());
-        for (unsigned int i = 0; i < tx.vin.size(); i++) {
-            const CTxIn &txin = tx.vin[i];
-            CCoins &coins = inputs.GetCoins(txin.prevout.hash);
+        BOOST_FOREACH(const CTxIn &txin, tx.vin) {
             txundo.vprevout.push_back(CTxInUndo());
-            ret = coins.Spend(txin.prevout, txundo.vprevout.back());
+            bool ret = inputs.ModifyCoins(txin.prevout.hash)->Spend(txin.prevout, txundo.vprevout.back());
             assert(ret);
         }
     }
 
     // add outputs
-    ret = inputs.SetCoins(tx.GetHash(), CCoins(tx, nHeight));
-    assert(ret);
+    inputs.ModifyCoins(tx.GetHash())->FromTx(tx, nHeight);
 }
 
 bool CScriptCheck::operator()() const {
@@ -1504,21 +1500,23 @@ bool DisconnectBlock(CBlock& block, CValidationState& state, CBlockIndex* pindex
         // exactly. Note that transactions with only provably unspendable outputs won't
         // have outputs available even in the block itself, so we handle that case
         // specially with outsEmpty.
+        {
         CCoins outsEmpty;
-        CCoins &outs = view.HaveCoins(hash) ? view.GetCoins(hash) : outsEmpty;
-        outs.ClearUnspendable();
+        CCoinsModifier outs = view.ModifyCoins(hash);
+        outs->ClearUnspendable();
 
-        CCoins outsBlock = CCoins(tx, pindex->nHeight);
+        CCoins outsBlock(tx, pindex->nHeight);
         // The CCoins serialization does not serialize negative numbers.
         // No network rules currently depend on the version here, so an inconsistency is harmless
         // but it must be corrected before txout nversion ever influences a network rule.
         if (outsBlock.nVersion < 0)
-            outs.nVersion = outsBlock.nVersion;
-        if (outs != outsBlock)
+            outs->nVersion = outsBlock.nVersion;
+        if (*outs != outsBlock)
             fClean = fClean && error("DisconnectBlock() : added transaction mismatch? database corrupted");
 
         // remove outputs
-        outs = CCoins();
+        outs->Clear();
+        }
 
         // restore inputs
         if (i > 0) { // not coinbases
@@ -1528,27 +1526,24 @@ bool DisconnectBlock(CBlock& block, CValidationState& state, CBlockIndex* pindex
             for (unsigned int j = tx.vin.size(); j-- > 0;) {
                 const COutPoint &out = tx.vin[j].prevout;
                 const CTxInUndo &undo = txundo.vprevout[j];
-                CCoins coins;
-                view.GetCoins(out.hash, coins); // this can fail if the prevout was already entirely spent
+                CCoinsModifier coins = view.ModifyCoins(out.hash);
                 if (undo.nHeight != 0) {
                     // undo data contains height: this is the last output of the prevout tx being spent
-                    if (!coins.IsPruned())
+                    if (!coins->IsPruned())
                         fClean = fClean && error("DisconnectBlock() : undo data overwriting existing transaction");
-                    coins = CCoins();
-                    coins.fCoinBase = undo.fCoinBase;
-                    coins.nHeight = undo.nHeight;
-                    coins.nVersion = undo.nVersion;
+                    coins->Clear();
+                    coins->fCoinBase = undo.fCoinBase;
+                    coins->nHeight = undo.nHeight;
+                    coins->nVersion = undo.nVersion;
                 } else {
-                    if (coins.IsPruned())
+                    if (coins->IsPruned())
                         fClean = fClean && error("DisconnectBlock() : undo data adding output to missing transaction");
                 }
-                if (coins.IsAvailable(out.n))
+                if (coins->IsAvailable(out.n))
                     fClean = fClean && error("DisconnectBlock() : undo data overwriting existing output");
-                if (coins.vout.size() < out.n+1)
-                    coins.vout.resize(out.n+1);
-                coins.vout[out.n] = undo.txout;
-                if (!view.SetCoins(out.hash, coins))
-                    return error("DisconnectBlock() : cannot restore coin inputs");
+                if (coins->vout.size() < out.n+1)
+                    coins->vout.resize(out.n+1);
+                coins->vout[out.n] = undo.txout;
             }
         }
     }

src/rpcrawtransaction.cpp

@@ -612,21 +612,19 @@ Value signrawtransaction(const Array& params, bool fHelp)
             vector<unsigned char> pkData(ParseHexO(prevOut, "scriptPubKey"));
             CScript scriptPubKey(pkData.begin(), pkData.end());
 
-            CCoins coins;
-            if (view.GetCoins(txid, coins)) {
-                if (coins.IsAvailable(nOut) && coins.vout[nOut].scriptPubKey != scriptPubKey) {
+            {
+                CCoinsModifier coins = view.ModifyCoins(txid);
+                if (coins->IsAvailable(nOut) && coins->vout[nOut].scriptPubKey != scriptPubKey) {
                     string err("Previous output scriptPubKey mismatch:\n");
-                    err = err + coins.vout[nOut].scriptPubKey.ToString() + "\nvs:\n"+
+                    err = err + coins->vout[nOut].scriptPubKey.ToString() + "\nvs:\n"+
                         scriptPubKey.ToString();
                     throw JSONRPCError(RPC_DESERIALIZATION_ERROR, err);
                 }
-                // what todo if txid is known, but the actual output isn't?
+                if ((unsigned int)nOut >= coins->vout.size())
+                    coins->vout.resize(nOut+1);
+                coins->vout[nOut].scriptPubKey = scriptPubKey;
+                coins->vout[nOut].nValue = 0; // we don't know the actual output value
             }
-            if ((unsigned int)nOut >= coins.vout.size())
-                coins.vout.resize(nOut+1);
-            coins.vout[nOut].scriptPubKey = scriptPubKey;
-            coins.vout[nOut].nValue = 0; // we don't know the actual output value
-            view.SetCoins(txid, coins);
 
             // if redeemScript given and not using the local wallet (private keys
             // given), add redeemScript to the tempKeystore so it can be signed: