Merge bitcoin/bitcoin#33866: refactor: Let CCoinsViewCache::BatchWrite return void

6da6f503a6 refactor: Let CCoinsViewCache::BatchWrite return void (TheCharlatan)

Pull request description:

  CCoinsViewCache::BatchWrite always returns true if called from a backed cache, so just return void instead. Also return void from ::Sync and ::Flush.

  This allows for dropping a FatalError condition and simplifying some dead error handling code a bit.

  Since we now no longer exercise the "error path" when returning from `CCoinsView::BatchWrite`, make the method clear the cache instead. This should only be exercised by tests and not change production behaviour. This might slightly improve the coins_view fuzz test's ability to generate better coverage.

ACKs for top commit:
  l0rinc:
    ACK 6da6f503a6
  andrewtoth:
    re-ACK 6da6f503a6
  achow101:
    ACK 6da6f503a6
  w0xlt:
    ACK 6da6f503a6

Tree-SHA512: dfaa325b0cf8108910aebf1b27434aaddb639d10d860e96797c77ea42eca9035a54a7dc1d6a5d4eae2b75fcc9356206d3d5672243d2c906e80d19024c8b95408

src/coins.cpp

@@ -16,7 +16,11 @@ TRACEPOINT_SEMAPHORE(utxocache, uncache);
 std::optional<Coin> CCoinsView::GetCoin(const COutPoint& outpoint) const { return std::nullopt; }
 uint256 CCoinsView::GetBestBlock() const { return uint256(); }
 std::vector<uint256> CCoinsView::GetHeadBlocks() const { return std::vector<uint256>(); }
-bool CCoinsView::BatchWrite(CoinsViewCacheCursor& cursor, const uint256 &hashBlock) { return false; }
+void CCoinsView::BatchWrite(CoinsViewCacheCursor& cursor, const uint256& hashBlock)
+{
+    for (auto it{cursor.Begin()}; it != cursor.End(); it = cursor.NextAndMaybeErase(*it)) { }
+}
+
 std::unique_ptr<CCoinsViewCursor> CCoinsView::Cursor() const { return nullptr; }
 
 bool CCoinsView::HaveCoin(const COutPoint &outpoint) const
@@ -30,7 +34,7 @@ bool CCoinsViewBacked::HaveCoin(const COutPoint &outpoint) const { return base->
 uint256 CCoinsViewBacked::GetBestBlock() const { return base->GetBestBlock(); }
 std::vector<uint256> CCoinsViewBacked::GetHeadBlocks() const { return base->GetHeadBlocks(); }
 void CCoinsViewBacked::SetBackend(CCoinsView &viewIn) { base = &viewIn; }
-bool CCoinsViewBacked::BatchWrite(CoinsViewCacheCursor& cursor, const uint256 &hashBlock) { return base->BatchWrite(cursor, hashBlock); }
+void CCoinsViewBacked::BatchWrite(CoinsViewCacheCursor& cursor, const uint256& hashBlock) { base->BatchWrite(cursor, hashBlock); }
 std::unique_ptr<CCoinsViewCursor> CCoinsViewBacked::Cursor() const { return base->Cursor(); }
 size_t CCoinsViewBacked::EstimateSize() const { return base->EstimateSize(); }
 
@@ -183,7 +187,8 @@ void CCoinsViewCache::SetBestBlock(const uint256 &hashBlockIn) {
     hashBlock = hashBlockIn;
 }
 
-bool CCoinsViewCache::BatchWrite(CoinsViewCacheCursor& cursor, const uint256 &hashBlockIn) {
+void CCoinsViewCache::BatchWrite(CoinsViewCacheCursor& cursor, const uint256& hashBlockIn)
+{
     for (auto it{cursor.Begin()}; it != cursor.End(); it = cursor.NextAndMaybeErase(*it)) {
         if (!it->second.IsDirty()) { // TODO a cursor can only contain dirty entries
             continue;
@@ -246,33 +251,27 @@ bool CCoinsViewCache::BatchWrite(CoinsViewCacheCursor& cursor, const uint256 &ha
         }
     }
     hashBlock = hashBlockIn;
-    return true;
 }
 
-bool CCoinsViewCache::Flush(bool will_reuse_cache) {
+void CCoinsViewCache::Flush(bool will_reuse_cache)
+{
     auto cursor{CoinsViewCacheCursor(m_sentinel, cacheCoins, /*will_erase=*/true)};
-    bool fOk = base->BatchWrite(cursor, hashBlock);
+    base->BatchWrite(cursor, hashBlock);
-    if (fOk) {
+    cacheCoins.clear();
-        cacheCoins.clear();
+    if (will_reuse_cache) {
-        if (will_reuse_cache) {
+        ReallocateCache();
-            ReallocateCache();
-        }
-        cachedCoinsUsage = 0;
     }
-    return fOk;
+    cachedCoinsUsage = 0;
 }
 
-bool CCoinsViewCache::Sync()
+void CCoinsViewCache::Sync()
 {
     auto cursor{CoinsViewCacheCursor(m_sentinel, cacheCoins, /*will_erase=*/false)};
-    bool fOk = base->BatchWrite(cursor, hashBlock);
+    base->BatchWrite(cursor, hashBlock);
-    if (fOk) {
+    if (m_sentinel.second.Next() != &m_sentinel) {
-        if (m_sentinel.second.Next() != &m_sentinel) {
+        /* BatchWrite must clear flags of all entries */
-            /* BatchWrite must clear flags of all entries */
+        throw std::logic_error("Not all unspent flagged entries were cleared");
-            throw std::logic_error("Not all unspent flagged entries were cleared");
-        }
     }
-    return fOk;
 }
 
 void CCoinsViewCache::Uncache(const COutPoint& hash)

src/coins.h

@@ -324,7 +324,7 @@ public:
 
     //! Do a bulk modification (multiple Coin changes + BestBlock change).
     //! The passed cursor is used to iterate through the coins.
-    virtual bool BatchWrite(CoinsViewCacheCursor& cursor, const uint256& hashBlock);
+    virtual void BatchWrite(CoinsViewCacheCursor& cursor, const uint256& hashBlock);
 
     //! Get a cursor to iterate over the whole state
     virtual std::unique_ptr<CCoinsViewCursor> Cursor() const;
@@ -350,7 +350,7 @@ public:
     uint256 GetBestBlock() const override;
     std::vector<uint256> GetHeadBlocks() const override;
     void SetBackend(CCoinsView &viewIn);
-    bool BatchWrite(CoinsViewCacheCursor& cursor, const uint256 &hashBlock) override;
+    void BatchWrite(CoinsViewCacheCursor& cursor, const uint256& hashBlock) override;
     std::unique_ptr<CCoinsViewCursor> Cursor() const override;
     size_t EstimateSize() const override;
 };
@@ -389,7 +389,7 @@ public:
     bool HaveCoin(const COutPoint &outpoint) const override;
     uint256 GetBestBlock() const override;
     void SetBestBlock(const uint256 &hashBlock);
-    bool BatchWrite(CoinsViewCacheCursor& cursor, const uint256 &hashBlock) override;
+    void BatchWrite(CoinsViewCacheCursor& cursor, const uint256& hashBlock) override;
     std::unique_ptr<CCoinsViewCursor> Cursor() const override {
         throw std::logic_error("CCoinsViewCache cursor iteration not supported.");
     }
@@ -441,18 +441,16 @@ public:
      * to be forgotten.
      * If will_reuse_cache is false, the cache will retain the same memory footprint
      * after flushing and should be destroyed to deallocate.
-     * If false is returned, the state of this cache (and its backing view) will be undefined.
      */
-    bool Flush(bool will_reuse_cache = true);
+    void Flush(bool will_reuse_cache = true);
 
     /**
      * Push the modifications applied to this cache to its base while retaining
      * the contents of this cache (except for spent coins, which we erase).
      * Failure to call this method or Flush() before destruction will cause the changes
      * to be forgotten.
-     * If false is returned, the state of this cache (and its backing view) will be undefined.
      */
-    bool Sync();
+    void Sync();
 
     /**
      * Removes the UTXO with the given outpoint from the cache, if it is

src/test/coins_tests.cpp

@@ -58,7 +58,7 @@ public:
 
     uint256 GetBestBlock() const override { return hashBestBlock_; }
 
-    bool BatchWrite(CoinsViewCacheCursor& cursor, const uint256& hashBlock) override
+    void BatchWrite(CoinsViewCacheCursor& cursor, const uint256& hashBlock) override
     {
         for (auto it{cursor.Begin()}; it != cursor.End(); it = cursor.NextAndMaybeErase(*it)){
             if (it->second.IsDirty()) {
@@ -72,7 +72,6 @@ public:
         }
         if (!hashBlock.IsNull())
             hashBestBlock_ = hashBlock;
-        return true;
     }
 };
 
@@ -237,7 +236,7 @@ void SimulationTest(CCoinsView* base, bool fake_best_block)
                 unsigned int flushIndex = m_rng.randrange(stack.size() - 1);
                 if (fake_best_block) stack[flushIndex]->SetBestBlock(m_rng.rand256());
                 bool should_erase = m_rng.randrange(4) < 3;
-                BOOST_CHECK(should_erase ? stack[flushIndex]->Flush() : stack[flushIndex]->Sync());
+                should_erase ? stack[flushIndex]->Flush() : stack[flushIndex]->Sync();
                 flushed_without_erase |= !should_erase;
             }
         }
@@ -247,7 +246,7 @@ void SimulationTest(CCoinsView* base, bool fake_best_block)
                 //Remove the top cache
                 if (fake_best_block) stack.back()->SetBestBlock(m_rng.rand256());
                 bool should_erase = m_rng.randrange(4) < 3;
-                BOOST_CHECK(should_erase ? stack.back()->Flush() : stack.back()->Sync());
+                should_erase ? stack.back()->Flush() : stack.back()->Sync();
                 flushed_without_erase |= !should_erase;
                 stack.pop_back();
             }
@@ -496,13 +495,13 @@ BOOST_FIXTURE_TEST_CASE(updatecoins_simulation_test, UpdateTest)
             // Every 100 iterations, flush an intermediate cache
             if (stack.size() > 1 && m_rng.randbool() == 0) {
                 unsigned int flushIndex = m_rng.randrange(stack.size() - 1);
-                BOOST_CHECK(stack[flushIndex]->Flush());
+                stack[flushIndex]->Flush();
             }
         }
         if (m_rng.randrange(100) == 0) {
             // Every 100 iterations, change the cache stack.
             if (stack.size() > 0 && m_rng.randbool() == 0) {
-                BOOST_CHECK(stack.back()->Flush());
+                stack.back()->Flush();
                 stack.pop_back();
             }
             if (stack.size() == 0 || (stack.size() < 4 && m_rng.randbool())) {
@@ -664,7 +663,7 @@ static void WriteCoinsViewEntry(CCoinsView& view, const MaybeCoin& cache_coin)
     CCoinsMap map{0, CCoinsMap::hasher{}, CCoinsMap::key_equal{}, &resource};
     if (cache_coin) InsertCoinsMapEntry(map, sentinel, *cache_coin);
     auto cursor{CoinsViewCacheCursor(sentinel, map, /*will_erase=*/true)};
-    BOOST_CHECK(view.BatchWrite(cursor, {}));
+    view.BatchWrite(cursor, {});
 }
 
 class SingleEntryCacheTest

src/test/fuzz/coins_view.cpp

@@ -74,10 +74,10 @@ void TestCoinsView(FuzzedDataProvider& fuzzed_data_provider, CCoinsView& backend
                 }
             },
             [&] {
-                (void)coins_view_cache.Flush(/*will_reuse_cache=*/fuzzed_data_provider.ConsumeBool());
+                coins_view_cache.Flush(/*will_reuse_cache=*/fuzzed_data_provider.ConsumeBool());
             },
             [&] {
-                (void)coins_view_cache.Sync();
+                coins_view_cache.Sync();
             },
             [&] {
                 uint256 best_block{ConsumeUInt256(fuzzed_data_provider)};

src/test/fuzz/coinscache_sim.cpp

@@ -163,7 +163,7 @@ public:
     std::unique_ptr<CCoinsViewCursor> Cursor() const final { return {}; }
     size_t EstimateSize() const final { return m_data.size(); }
 
-    bool BatchWrite(CoinsViewCacheCursor& cursor, const uint256&) final
+    void BatchWrite(CoinsViewCacheCursor& cursor, const uint256&) final
     {
         for (auto it{cursor.Begin()}; it != cursor.End(); it = cursor.NextAndMaybeErase(*it)) {
             if (it->second.IsDirty()) {
@@ -187,7 +187,6 @@ public:
                 }
             }
         }
-        return true;
     }
 };
 

src/test/validation_flush_tests.cpp

@@ -60,7 +60,7 @@ BOOST_AUTO_TEST_CASE(getcoinscachesizestate)
     // CRITICAL → OK via Flush
     BOOST_CHECK_EQUAL(chainstate.GetCoinsCacheSizeState(MAX_COINS_BYTES, /*max_mempool_size_bytes=*/0), CoinsCacheSizeState::CRITICAL);
     view.SetBestBlock(m_rng.rand256());
-    BOOST_REQUIRE(view.Flush());
+    view.Flush();
     BOOST_CHECK_EQUAL(chainstate.GetCoinsCacheSizeState(MAX_COINS_BYTES, /*max_mempool_size_bytes=*/0), CoinsCacheSizeState::OK);
 }
 

src/txdb.cpp

@@ -90,7 +90,8 @@ std::vector<uint256> CCoinsViewDB::GetHeadBlocks() const {
     return vhashHeadBlocks;
 }
 
-bool CCoinsViewDB::BatchWrite(CoinsViewCacheCursor& cursor, const uint256 &hashBlock) {
+void CCoinsViewDB::BatchWrite(CoinsViewCacheCursor& cursor, const uint256& hashBlock)
+{
     CDBBatch batch(*m_db);
     size_t count = 0;
     size_t changed = 0;
@@ -151,7 +152,6 @@ bool CCoinsViewDB::BatchWrite(CoinsViewCacheCursor& cursor, const uint256 &hashB
     LogDebug(BCLog::COINDB, "Writing final batch of %.2f MiB\n", batch.ApproximateSize() * (1.0 / 1048576.0));
     m_db->WriteBatch(batch);
     LogDebug(BCLog::COINDB, "Committed %u changed transaction outputs (out of %u) to coin database...\n", (unsigned int)changed, (unsigned int)count);
-    return true;
 }
 
 size_t CCoinsViewDB::EstimateSize() const

src/txdb.h

@@ -44,7 +44,7 @@ public:
     bool HaveCoin(const COutPoint &outpoint) const override;
     uint256 GetBestBlock() const override;
     std::vector<uint256> GetHeadBlocks() const override;
-    bool BatchWrite(CoinsViewCacheCursor& cursor, const uint256 &hashBlock) override;
+    void BatchWrite(CoinsViewCacheCursor& cursor, const uint256& hashBlock) override;
     std::unique_ptr<CCoinsViewCursor> Cursor() const override;
 
     //! Whether an unsupported database format is used.

src/validation.cpp

@@ -2845,9 +2845,7 @@ bool Chainstate::FlushStateToDisk(
                 }
                 // Flush the chainstate (which may refer to block index entries).
                 const auto empty_cache{(mode == FlushStateMode::ALWAYS) || fCacheLarge || fCacheCritical};
-                if (empty_cache ? !CoinsTip().Flush() : !CoinsTip().Sync()) {
+                empty_cache ? CoinsTip().Flush() : CoinsTip().Sync();
-                    return FatalError(m_chainman.GetNotifications(), state, _("Failed to write to coin database."));
-                }
                 full_flush_completed = true;
                 TRACEPOINT(utxocache, flush,
                     int64_t{Ticks<std::chrono::microseconds>(NodeClock::now() - nNow)},
@@ -2984,8 +2982,7 @@ bool Chainstate::DisconnectTip(BlockValidationState& state, DisconnectedBlockTra
             LogError("DisconnectTip(): DisconnectBlock %s failed\n", pindexDelete->GetBlockHash().ToString());
             return false;
         }
-        bool flushed = view.Flush(/*will_reuse_cache=*/false); // local CCoinsViewCache goes out of scope
+        view.Flush(/*will_reuse_cache=*/false); // local CCoinsViewCache goes out of scope
-        assert(flushed);
     }
     LogDebug(BCLog::BENCH, "- Disconnect block: %.2fms\n",
              Ticks<MillisecondsDouble>(SteadyClock::now() - time_start));
@@ -3119,8 +3116,7 @@ bool Chainstate::ConnectTip(
                  Ticks<MillisecondsDouble>(time_3 - time_2),
                  Ticks<SecondsDouble>(m_chainman.time_connect_total),
                  Ticks<MillisecondsDouble>(m_chainman.time_connect_total) / m_chainman.num_blocks_total);
-        bool flushed = view.Flush(/*will_reuse_cache=*/false); // local CCoinsViewCache goes out of scope
+        view.Flush(/*will_reuse_cache=*/false); // local CCoinsViewCache goes out of scope
-        assert(flushed);
     }
     const auto time_4{SteadyClock::now()};
     m_chainman.time_flush += time_4 - time_3;