txdb: Add Cursor() method to CCoinsView to iterate over UTXO set

Add a method Cursor() to CCoinsView that returns a cursor which can be
used to iterate over the whole UTXO set.

- rpc: Change gettxoutsetinfo to use new Cursor method

- txdb: Remove GetStats method - Now that GetStats is implemented in
  terms of Cursor, remove it.

src/coins.cpp

@@ -45,7 +45,7 @@ bool CCoinsView::GetCoins(const uint256 &txid, CCoins &coins) const { return fal
 bool CCoinsView::HaveCoins(const uint256 &txid) const { return false; }
 uint256 CCoinsView::GetBestBlock() const { return uint256(); }
 bool CCoinsView::BatchWrite(CCoinsMap &mapCoins, const uint256 &hashBlock) { return false; }
-bool CCoinsView::GetStats(CCoinsStats &stats) const { return false; }
+CCoinsViewCursor *CCoinsView::Cursor() const { return 0; }
 
 
 CCoinsViewBacked::CCoinsViewBacked(CCoinsView *viewIn) : base(viewIn) { }
@@ -54,7 +54,7 @@ bool CCoinsViewBacked::HaveCoins(const uint256 &txid) const { return base->HaveC
 uint256 CCoinsViewBacked::GetBestBlock() const { return base->GetBestBlock(); }
 void CCoinsViewBacked::SetBackend(CCoinsView &viewIn) { base = &viewIn; }
 bool CCoinsViewBacked::BatchWrite(CCoinsMap &mapCoins, const uint256 &hashBlock) { return base->BatchWrite(mapCoins, hashBlock); }
-bool CCoinsViewBacked::GetStats(CCoinsStats &stats) const { return base->GetStats(stats); }
+CCoinsViewCursor *CCoinsViewBacked::Cursor() const { return base->Cursor(); }
 
 CCoinsKeyHasher::CCoinsKeyHasher() : salt(GetRandHash()) {}
 
@@ -300,3 +300,7 @@ CCoinsModifier::~CCoinsModifier()
         cache.cachedCoinsUsage += it->second.coins.DynamicMemoryUsage();
     }
 }
+
+CCoinsViewCursor::~CCoinsViewCursor()
+{
+}

src/coins.h

@@ -297,20 +297,27 @@ struct CCoinsCacheEntry
 
 typedef boost::unordered_map<uint256, CCoinsCacheEntry, CCoinsKeyHasher> CCoinsMap;
 
-struct CCoinsStats
+/** Cursor for iterating over CoinsView state */
+class CCoinsViewCursor
 {
-    int nHeight;
+public:
+    CCoinsViewCursor(const uint256 &hashBlockIn): hashBlock(hashBlockIn) {}
+    virtual ~CCoinsViewCursor();
+
+    virtual bool GetKey(uint256 &key) const = 0;
+    virtual bool GetValue(CCoins &coins) const = 0;
+    /* Don't care about GetKeySize here */
+    virtual unsigned int GetValueSize() const = 0;
+
+    virtual bool Valid() const = 0;
+    virtual void Next() = 0;
+
+    //! Get best block at the time this cursor was created
+    const uint256 &GetBestBlock() const { return hashBlock; }
+private:
     uint256 hashBlock;
-    uint64_t nTransactions;
-    uint64_t nTransactionOutputs;
-    uint64_t nSerializedSize;
-    uint256 hashSerialized;
-    CAmount nTotalAmount;
-
-    CCoinsStats() : nHeight(0), nTransactions(0), nTransactionOutputs(0), nSerializedSize(0), nTotalAmount(0) {}
 };
 
-
 /** Abstract view on the open txout dataset. */
 class CCoinsView
 {
@@ -329,8 +336,8 @@ public:
     //! The passed mapCoins can be modified.
     virtual bool BatchWrite(CCoinsMap &mapCoins, const uint256 &hashBlock);
 
-    //! Calculate statistics about the unspent transaction output set
-    virtual bool GetStats(CCoinsStats &stats) const;
+    //! Get a cursor to iterate over the whole state
+    virtual CCoinsViewCursor *Cursor() const;
 
     //! As we use CCoinsViews polymorphically, have a virtual destructor
     virtual ~CCoinsView() {}
@@ -350,7 +357,7 @@ public:
     uint256 GetBestBlock() const;
     void SetBackend(CCoinsView &viewIn);
     bool BatchWrite(CCoinsMap &mapCoins, const uint256 &hashBlock);
-    bool GetStats(CCoinsStats &stats) const;
+    CCoinsViewCursor *Cursor() const;
 };
 
 

src/rpc/blockchain.cpp

@@ -18,11 +18,14 @@
 #include "txmempool.h"
 #include "util.h"
 #include "utilstrencodings.h"
+#include "hash.h"
 
 #include <stdint.h>
 
 #include <univalue.h>
 
+#include <boost/thread/thread.hpp> // boost::thread::interrupt
+
 using namespace std;
 
 extern void TxToJSON(const CTransaction& tx, const uint256 hashBlock, UniValue& entry);
@@ -432,6 +435,59 @@ UniValue getblock(const UniValue& params, bool fHelp)
     return blockToJSON(block, pblockindex);
 }
 
+struct CCoinsStats
+{
+    int nHeight;
+    uint256 hashBlock;
+    uint64_t nTransactions;
+    uint64_t nTransactionOutputs;
+    uint64_t nSerializedSize;
+    uint256 hashSerialized;
+    CAmount nTotalAmount;
+
+    CCoinsStats() : nHeight(0), nTransactions(0), nTransactionOutputs(0), nSerializedSize(0), nTotalAmount(0) {}
+};
+
+//! Calculate statistics about the unspent transaction output set
+static bool GetUTXOStats(CCoinsView *view, CCoinsStats &stats)
+{
+    boost::scoped_ptr<CCoinsViewCursor> pcursor(view->Cursor());
+
+    CHashWriter ss(SER_GETHASH, PROTOCOL_VERSION);
+    stats.hashBlock = pcursor->GetBestBlock();
+    {
+        LOCK(cs_main);
+        stats.nHeight = mapBlockIndex.find(stats.hashBlock)->second->nHeight;
+    }
+    ss << stats.hashBlock;
+    CAmount nTotalAmount = 0;
+    while (pcursor->Valid()) {
+        boost::this_thread::interruption_point();
+        uint256 key;
+        CCoins coins;
+        if (pcursor->GetKey(key) && pcursor->GetValue(coins)) {
+            stats.nTransactions++;
+            for (unsigned int i=0; i<coins.vout.size(); i++) {
+                const CTxOut &out = coins.vout[i];
+                if (!out.IsNull()) {
+                    stats.nTransactionOutputs++;
+                    ss << VARINT(i+1);
+                    ss << out;
+                    nTotalAmount += out.nValue;
+                }
+            }
+            stats.nSerializedSize += 32 + pcursor->GetValueSize();
+            ss << VARINT(0);
+        } else {
+            return error("%s: unable to read value", __func__);
+        }
+        pcursor->Next();
+    }
+    stats.hashSerialized = ss.GetHash();
+    stats.nTotalAmount = nTotalAmount;
+    return true;
+}
+
 UniValue gettxoutsetinfo(const UniValue& params, bool fHelp)
 {
     if (fHelp || params.size() != 0)
@@ -458,7 +514,7 @@ UniValue gettxoutsetinfo(const UniValue& params, bool fHelp)
 
     CCoinsStats stats;
     FlushStateToDisk();
-    if (pcoinsTip->GetStats(stats)) {
+    if (GetUTXOStats(pcoinsTip, stats)) {
         ret.push_back(Pair("height", (int64_t)stats.nHeight));
         ret.push_back(Pair("bestblock", stats.hashBlock.GetHex()));
         ret.push_back(Pair("transactions", (int64_t)stats.nTransactions));

src/test/coins_tests.cpp

@@ -61,8 +61,6 @@ public:
             hashBestBlock_ = hashBlock;
         return true;
     }
-
-    bool GetStats(CCoinsStats& stats) const { return false; }
 };
 
 class CCoinsViewCacheTest : public CCoinsViewCache

src/txdb.cpp

@@ -94,51 +94,53 @@ bool CBlockTreeDB::ReadLastBlockFile(int &nFile) {
     return Read(DB_LAST_BLOCK, nFile);
 }
 
-bool CCoinsViewDB::GetStats(CCoinsStats &stats) const {
+CCoinsViewCursor *CCoinsViewDB::Cursor() const
+{
+    CCoinsViewDBCursor *i = new CCoinsViewDBCursor(const_cast<CDBWrapper*>(&db)->NewIterator(), GetBestBlock());
     /* It seems that there are no "const iterators" for LevelDB.  Since we
        only need read operations on it, use a const-cast to get around
        that restriction.  */
-    boost::scoped_ptr<CDBIterator> pcursor(const_cast<CDBWrapper*>(&db)->NewIterator());
-    pcursor->Seek(DB_COINS);
+    i->pcursor->Seek(DB_COINS);
+    // Cache key of first record
+    i->pcursor->GetKey(i->keyTmp);
+    return i;
+}
 
-    CHashWriter ss(SER_GETHASH, PROTOCOL_VERSION);
-    stats.hashBlock = GetBestBlock();
-    ss << stats.hashBlock;
-    CAmount nTotalAmount = 0;
-    while (pcursor->Valid()) {
-        boost::this_thread::interruption_point();
-        std::pair<char, uint256> key;
-        CCoins coins;
-        if (pcursor->GetKey(key) && key.first == DB_COINS) {
-            if (pcursor->GetValue(coins)) {
-                stats.nTransactions++;
-                for (unsigned int i=0; i<coins.vout.size(); i++) {
-                    const CTxOut &out = coins.vout[i];
-                    if (!out.IsNull()) {
-                        stats.nTransactionOutputs++;
-                        ss << VARINT(i+1);
-                        ss << out;
-                        nTotalAmount += out.nValue;
-                    }
-                }
-                stats.nSerializedSize += 32 + pcursor->GetValueSize();
-                ss << VARINT(0);
-            } else {
-                return error("CCoinsViewDB::GetStats() : unable to read value");
-            }
-        } else {
-            break;
-        }
-        pcursor->Next();
-    }
+bool CCoinsViewDBCursor::GetKey(uint256 &key) const
 {
-        LOCK(cs_main);
-        stats.nHeight = mapBlockIndex.find(stats.hashBlock)->second->nHeight;
-    }
-    stats.hashSerialized = ss.GetHash();
-    stats.nTotalAmount = nTotalAmount;
+    // Return cached key
+    if (keyTmp.first == DB_COINS) {
+        key = keyTmp.second;
         return true;
     }
+    return false;
+}
+
+bool CCoinsViewDBCursor::GetValue(CCoins &coins) const
+{
+    return pcursor->GetValue(coins);
+}
+
+unsigned int CCoinsViewDBCursor::GetValueSize() const
+{
+    return pcursor->GetValueSize();
+}
+
+bool CCoinsViewDBCursor::Valid() const
+{
+    return keyTmp.first == DB_COINS;
+}
+
+void CCoinsViewDBCursor::Next()
+{
+    pcursor->Next();
+    if (pcursor->Valid()) {
+        bool ok = pcursor->GetKey(keyTmp);
+        assert(ok); // If GetKey fails here something must be wrong with underlying database, we cannot handle that here
+    } else {
+        keyTmp.first = 0; // Invalidate cached key after last record so that Valid() and GetKey() return false
+    }
+}
 
 bool CBlockTreeDB::WriteBatchSync(const std::vector<std::pair<int, const CBlockFileInfo*> >& fileInfo, int nLastFile, const std::vector<const CBlockIndex*>& blockinfo) {
     CDBBatch batch(&GetObfuscateKey());

src/txdb.h

@@ -26,6 +26,8 @@ static const int64_t nMaxDbCache = sizeof(void*) > 4 ? 16384 : 1024;
 //! min. -dbcache in (MiB)
 static const int64_t nMinDbCache = 4;
 
+class CCoinsViewDBCursor;
+
 /** CCoinsView backed by the coin database (chainstate/) */
 class CCoinsViewDB : public CCoinsView
 {
@@ -38,7 +40,29 @@ public:
     bool HaveCoins(const uint256 &txid) const;
     uint256 GetBestBlock() const;
     bool BatchWrite(CCoinsMap &mapCoins, const uint256 &hashBlock);
-    bool GetStats(CCoinsStats &stats) const;
+    CCoinsViewCursor *Cursor() const;
+};
+
+/** Specialization of CCoinsViewCursor to iterate over a CCoinsViewDB */
+class CCoinsViewDBCursor: public CCoinsViewCursor
+{
+public:
+    ~CCoinsViewDBCursor() {}
+
+    bool GetKey(uint256 &key) const;
+    bool GetValue(CCoins &coins) const;
+    unsigned int GetValueSize() const;
+
+    bool Valid() const;
+    void Next();
+
+private:
+    CCoinsViewDBCursor(CDBIterator* pcursorIn, const uint256 &hashBlockIn):
+        CCoinsViewCursor(hashBlockIn), pcursor(pcursorIn) {}
+    boost::scoped_ptr<CDBIterator> pcursor;
+    std::pair<char, uint256> keyTmp;
+
+    friend class CCoinsViewDB;
 };
 
 /** Access to the block database (blocks/index/) */