Merge bitcoin/bitcoin#30884: streams: cache file position within AutoFile

a240e15 streams: remove AutoFile::Get() entirely (Pieter Wuille)
e624a9b streams: cache file position within AutoFile (Pieter Wuille)

Pull request description:

  Fixes #30833.

  Instead of relying on frequent `ftell` calls (which appear to cause a significant slowdown on some systems) in XOR-enabled `AutoFile`s, cache the file position within `AutoFile` itself.

ACKs for top commit:
  achow101:
    ACK a240e15
  davidgumberg:
    untested reACK bitcoin/bitcoin@a240e15
  theStack:
    Code-review ACK a240e15

Tree-SHA512: fd3681edc018afaf955dc7a41a0c953ca80d46c1129e3c5b306c87c95aae93b2fe7b900794eb8b6f10491f9211645e7939918a28838295e6873eb226fca7006f

Author: achow101

src/addrdb.cpp

@@ -73,7 +73,7 @@ bool SerializeFileDB(const std::string& prefix, const fs::path& path, const Data
         remove(pathTmp);
         return false;
     }
-    if (!FileCommit(fileout.Get())) {
+    if (!fileout.Commit()) {
         fileout.fclose();
         remove(pathTmp);
         LogError("%s: Failed to flush file %s\n", __func__, fs::PathToString(pathTmp));

src/bench/streams_findbyte.cpp

@@ -19,7 +19,7 @@ static void FindByte(benchmark::Bench& bench)
     uint8_t data[file_size] = {0};
     data[file_size-1] = 1;
     file << data;
-    std::rewind(file.Get());
+    file.seek(0, SEEK_SET);
     BufferedFile bf{file, /*nBufSize=*/file_size + 1, /*nRewindIn=*/file_size};
 
     bench.run([&] {

src/index/blockfilterindex.cpp

@@ -151,7 +151,7 @@ bool BlockFilterIndex::CustomCommit(CDBBatch& batch)
         LogError("%s: Failed to open filter file %d\n", __func__, pos.nFile);
         return false;
     }
-    if (!FileCommit(file.Get())) {
+    if (!file.Commit()) {
         LogError("%s: Failed to commit filter file %d\n", __func__, pos.nFile);
         return false;
     }
@@ -201,11 +201,11 @@ size_t BlockFilterIndex::WriteFilterToDisk(FlatFilePos& pos, const BlockFilter&
             LogPrintf("%s: Failed to open filter file %d\n", __func__, pos.nFile);
             return 0;
         }
-        if (!TruncateFile(last_file.Get(), pos.nPos)) {
+        if (!last_file.Truncate(pos.nPos)) {
             LogPrintf("%s: Failed to truncate filter file %d\n", __func__, pos.nFile);
             return 0;
         }
-        if (!FileCommit(last_file.Get())) {
+        if (!last_file.Commit()) {
             LogPrintf("%s: Failed to commit filter file %d\n", __func__, pos.nFile);
             return 0;
         }

src/index/txindex.cpp

@@ -87,10 +87,7 @@ bool TxIndex::FindTx(const uint256& tx_hash, uint256& block_hash, CTransactionRe
     CBlockHeader header;
     try {
         file >> header;
-        if (fseek(file.Get(), postx.nTxOffset, SEEK_CUR)) {
-            LogError("%s: fseek(...) failed\n", __func__);
-            return false;
-        }
+        file.seek(postx.nTxOffset, SEEK_CUR);
         file >> TX_WITH_WITNESS(tx);
     } catch (const std::exception& e) {
         LogError("%s: Deserialize or I/O error - %s\n", __func__, e.what());

src/node/blockstorage.cpp

@@ -683,7 +683,7 @@ bool BlockManager::UndoWriteToDisk(const CBlockUndo& blockundo, FlatFilePos& pos
     fileout << GetParams().MessageStart() << nSize;
 
     // Write undo data
-    long fileOutPos = ftell(fileout.Get());
+    long fileOutPos = fileout.tell();
     if (fileOutPos < 0) {
         LogError("%s: ftell failed\n", __func__);
         return false;
@@ -981,7 +981,7 @@ bool BlockManager::WriteBlockToDisk(const CBlock& block, FlatFilePos& pos) const
     fileout << GetParams().MessageStart() << nSize;
 
     // Write block
-    long fileOutPos = ftell(fileout.Get());
+    long fileOutPos = fileout.tell();
     if (fileOutPos < 0) {
         LogError("%s: ftell failed\n", __func__);
         return false;

src/node/mempool_persist.cpp

@@ -199,8 +199,8 @@ bool DumpMempool(const CTxMemPool& pool, const fs::path& dump_path, FopenFn mock
         LogInfo("Writing %d unbroadcast transactions to file.\n", unbroadcast_txids.size());
         file << unbroadcast_txids;
 
-        if (!skip_file_commit && !FileCommit(file.Get()))
-            throw std::runtime_error("FileCommit failed");
+        if (!skip_file_commit && !file.Commit())
+            throw std::runtime_error("Commit failed");
         file.fclose();
         if (!RenameOver(dump_path + ".new", dump_path)) {
             throw std::runtime_error("Rename failed");

src/node/utxo_snapshot.cpp

@@ -73,9 +73,11 @@ std::optional<uint256> ReadSnapshotBaseBlockhash(fs::path chaindir)
     }
     afile >> base_blockhash;
 
-    if (std::fgetc(afile.Get()) != EOF) {
+    int64_t position = afile.tell();
+    afile.seek(0, SEEK_END);
+    if (position != afile.tell()) {
         LogPrintf("[snapshot] warning: unexpected trailing data in %s\n", read_from_str);
-    } else if (std::ferror(afile.Get())) {
+    } else if (afile.IsError()) {
         LogPrintf("[snapshot] warning: i/o error reading %s\n", read_from_str);
     }
     return base_blockhash;

src/streams.cpp

@@ -4,21 +4,29 @@
 
 #include <span.h>
 #include <streams.h>
+#include <util/fs_helpers.h>
 
 #include <array>
 
+AutoFile::AutoFile(std::FILE* file, std::vector<std::byte> data_xor)
+    : m_file{file}, m_xor{std::move(data_xor)}
+{
+    if (!IsNull()) {
+        auto pos{std::ftell(m_file)};
+        if (pos >= 0) m_position = pos;
+    }
+}
+
 std::size_t AutoFile::detail_fread(Span<std::byte> dst)
 {
     if (!m_file) throw std::ios_base::failure("AutoFile::read: file handle is nullptr");
-    if (m_xor.empty()) {
-        return std::fread(dst.data(), 1, dst.size(), m_file);
-    } else {
-        const auto init_pos{std::ftell(m_file)};
-        if (init_pos < 0) throw std::ios_base::failure("AutoFile::read: ftell failed");
-        std::size_t ret{std::fread(dst.data(), 1, dst.size(), m_file)};
-        util::Xor(dst.subspan(0, ret), m_xor, init_pos);
-        return ret;
+    size_t ret = std::fread(dst.data(), 1, dst.size(), m_file);
+    if (!m_xor.empty()) {
+        if (!m_position.has_value()) throw std::ios_base::failure("AutoFile::read: position unknown");
+        util::Xor(dst.subspan(0, ret), m_xor, *m_position);
     }
+    if (m_position.has_value()) *m_position += ret;
+    return ret;
 }
 
 void AutoFile::seek(int64_t offset, int origin)
@@ -29,18 +37,23 @@ void AutoFile::seek(int64_t offset, int origin)
     if (std::fseek(m_file, offset, origin) != 0) {
         throw std::ios_base::failure(feof() ? "AutoFile::seek: end of file" : "AutoFile::seek: fseek failed");
     }
+    if (origin == SEEK_SET) {
+        m_position = offset;
+    } else if (origin == SEEK_CUR && m_position.has_value()) {
+        *m_position += offset;
+    } else {
+        int64_t r{std::ftell(m_file)};
+        if (r < 0) {
+            throw std::ios_base::failure("AutoFile::seek: ftell failed");
+        }
+        m_position = r;
+    }
 }
 
 int64_t AutoFile::tell()
 {
-    if (IsNull()) {
-        throw std::ios_base::failure("AutoFile::tell: file handle is nullptr");
-    }
-    int64_t r{std::ftell(m_file)};
-    if (r < 0) {
-        throw std::ios_base::failure("AutoFile::tell: ftell failed");
-    }
-    return r;
+    if (!m_position.has_value()) throw std::ios_base::failure("AutoFile::tell: position unknown");
+    return *m_position;
 }
 
 void AutoFile::read(Span<std::byte> dst)
@@ -60,6 +73,7 @@ void AutoFile::ignore(size_t nSize)
             throw std::ios_base::failure(feof() ? "AutoFile::ignore: end of file" : "AutoFile::ignore: fread failed");
         }
         nSize -= nNow;
+        if (m_position.has_value()) *m_position += nNow;
     }
 }
 
@@ -70,19 +84,34 @@ void AutoFile::write(Span<const std::byte> src)
         if (std::fwrite(src.data(), 1, src.size(), m_file) != src.size()) {
             throw std::ios_base::failure("AutoFile::write: write failed");
         }
+        if (m_position.has_value()) *m_position += src.size();
     } else {
-        auto current_pos{std::ftell(m_file)};
-        if (current_pos < 0) throw std::ios_base::failure("AutoFile::write: ftell failed");
+        if (!m_position.has_value()) throw std::ios_base::failure("AutoFile::write: position unknown");
         std::array<std::byte, 4096> buf;
         while (src.size() > 0) {
             auto buf_now{Span{buf}.first(std::min<size_t>(src.size(), buf.size()))};
             std::copy(src.begin(), src.begin() + buf_now.size(), buf_now.begin());
-            util::Xor(buf_now, m_xor, current_pos);
+            util::Xor(buf_now, m_xor, *m_position);
             if (std::fwrite(buf_now.data(), 1, buf_now.size(), m_file) != buf_now.size()) {
                 throw std::ios_base::failure{"XorFile::write: failed"};
             }
             src = src.subspan(buf_now.size());
-            current_pos += buf_now.size();
+            *m_position += buf_now.size();
         }
     }
 }
+
+bool AutoFile::Commit()
+{
+    return ::FileCommit(m_file);
+}
+
+bool AutoFile::IsError()
+{
+    return ferror(m_file);
+}
+
+bool AutoFile::Truncate(unsigned size)
+{
+    return ::TruncateFile(m_file, size);
+}

src/streams.h

@@ -390,9 +390,10 @@ class AutoFile
 protected:
     std::FILE* m_file;
     std::vector<std::byte> m_xor;
+    std::optional<int64_t> m_position;
 
 public:
-    explicit AutoFile(std::FILE* file, std::vector<std::byte> data_xor={}) : m_file{file}, m_xor{std::move(data_xor)} {}
+    explicit AutoFile(std::FILE* file, std::vector<std::byte> data_xor={});
 
     ~AutoFile() { fclose(); }
 
@@ -419,12 +420,6 @@ class AutoFile
         return ret;
     }
 
-    /** Get wrapped FILE* without transfer of ownership.
-     * @note Ownership of the FILE* will remain with this class. Use this only if the scope of the
-     * AutoFile outlives use of the passed pointer.
-     */
-    std::FILE* Get() const { return m_file; }
-
     /** Return true if the wrapped FILE* is nullptr, false otherwise.
      */
     bool IsNull() const { return m_file == nullptr; }
@@ -458,6 +453,10 @@ class AutoFile
         ::Unserialize(*this, obj);
         return *this;
     }
+
+    bool Commit();
+    bool IsError();
+    bool Truncate(unsigned size);
 };
 
 /** Wrapper around an AutoFile& that implements a ring buffer to

src/test/fuzz/autofile.cpp

@@ -56,7 +56,6 @@ FUZZ_TARGET(autofile)
                 WriteToStream(fuzzed_data_provider, auto_file);
             });
     }
-    (void)auto_file.Get();
     (void)auto_file.IsNull();
     if (fuzzed_data_provider.ConsumeBool()) {
         FILE* f = auto_file.release();