Return 0 instead of -1 from hash_table getBytes()

The hash_table implementation cannot accurately track memory usage and was
returning -1 from ConflictSet::getBytes() and ConflictSet_getBytes(). That
violates the API contract that getBytes() returns a non-negative byte count.

Change both entry points to return 0 and document in ConflictSet.h that
implementations which do not track memory usage may return 0.

Add a regression test in test_conflict_set.py that loads the hash_table
implementation and verifies getBytes() is non-negative.

Closes #62

.gitea/workflows/ci.yml

@@ -2,62 +2,44 @@ name: CI
 
 on: [push, pull_request]
 
+env:
+  CC: clang
+  CXX: clang++
+
 jobs:
-  build-image:
-    strategy:
-      fail-fast: false
-      matrix:
-        include:
-          - runner: ubuntu-latest-amd64
-            arch: amd64
-          - runner: ubuntu-latest-arm64
-            arch: arm64
-    runs-on: ${{ matrix.runner }}
-    steps:
-      - uses: actions/checkout@v4
-
-      - name: Log in to registry
-        env:
-          REGISTRY_USER: ${{ secrets.REGISTRY_USER }}
-          REGISTRY_TOKEN: ${{ secrets.REGISTRY_TOKEN }}
-        run: |
-          echo "$REGISTRY_TOKEN" \
-            | docker login -u "$REGISTRY_USER" --password-stdin git.weaselab.dev
-
-      - name: Build and push image if changed
-        run: |
-          image=git.weaselab.dev/weaselab/conflict-set-ci
-          hash="$(sha256sum Dockerfile .pre-commit-config.yaml | sha256sum | cut -c 1-16)"
-          latest="$image:latest-${{ matrix.arch }}"
-          current="$(docker buildx imagetools inspect "$latest" \
-            --format '{{index .Image.Config.Labels "dev.weaselab.ci-hash"}}' 2> /dev/null || true)"
-          if [ "$current" = "$hash" ]; then
-            echo "$latest is up to date"
-          else
-            docker build --push --label "dev.weaselab.ci-hash=$hash" -t "$latest" .
-          fi
-
   pre-commit:
-    needs: build-image
     runs-on: ubuntu-latest-amd64
-    container:
-      image: git.weaselab.dev/weaselab/conflict-set-ci:latest-amd64
-      credentials:
-        username: ${{ secrets.REGISTRY_USER }}
-        password: ${{ secrets.REGISTRY_TOKEN }}
     steps:
       - uses: actions/checkout@v4
 
+      - uses: actions/cache@v4
+        with:
+          path: /var/cache/apt/archives
+          key: apt-amd64-${{ hashFiles('.gitea/workflows/ci.yml') }}
+
+      - name: Install dependencies
+        run: |
+          . /etc/os-release
+          wget -qO- https://apt.llvm.org/llvm-snapshot.gpg.key | sudo tee /etc/apt/trusted.gpg.d/apt.llvm.org.asc
+          echo "deb http://apt.llvm.org/${VERSION_CODENAME}/ llvm-toolchain-${VERSION_CODENAME}-21 main" | sudo tee /etc/apt/sources.list.d/llvm.list
+          sudo apt-get update -qq
+          sudo apt-get install -y \
+            clang-21 git nodejs pre-commit
+          for tool in clang clang++; do
+            sudo update-alternatives --install /usr/bin/${tool} ${tool} /usr/bin/${tool}-21 100
+          done
+
+      - uses: actions/cache@v4
+        with:
+          path: ~/.cache/pre-commit
+          key: pre-commit-${{ hashFiles('.pre-commit-config.yaml') }}
+
       - name: Run pre-commit
-        env:
-          # use the hooks pre-installed in the image
-          HOME: /tmp
         run: |
           git config --global --add safe.directory "$PWD"
           pre-commit run --all-files --show-diff-on-failure
 
   test:
-    needs: build-image
     strategy:
       fail-fast: false
       matrix:
@@ -71,14 +53,29 @@ jobs:
           - name: gcc
             cmake_args: -DCMAKE_C_COMPILER=gcc -DCMAKE_CXX_COMPILER=g++
     runs-on: ubuntu-latest-amd64
-    container:
-      image: git.weaselab.dev/weaselab/conflict-set-ci:latest-amd64
-      credentials:
-        username: ${{ secrets.REGISTRY_USER }}
-        password: ${{ secrets.REGISTRY_TOKEN }}
     steps:
       - uses: actions/checkout@v4
 
+      - uses: actions/cache@v4
+        with:
+          path: /var/cache/apt/archives
+          key: apt-amd64-${{ hashFiles('.gitea/workflows/ci.yml') }}
+
+      - name: Install dependencies
+        run: |
+          . /etc/os-release
+          wget -qO- https://apt.llvm.org/llvm-snapshot.gpg.key | sudo tee /etc/apt/trusted.gpg.d/apt.llvm.org.asc
+          echo "deb http://apt.llvm.org/${VERSION_CODENAME}/ llvm-toolchain-${VERSION_CODENAME}-21 main" | sudo tee /etc/apt/sources.list.d/llvm.list
+          sudo apt-get update -qq
+          sudo apt-get install -y \
+            build-essential ccache clang-21 cmake gcc g++ \
+            libc6-dbg llvm-21 lld-21 mold ninja-build python3 valgrind zstd
+          sudo curl -Ls "https://dl.min.io/client/mc/release/linux-amd64/mc" \
+            -o /usr/local/bin/mc && sudo chmod +x /usr/local/bin/mc
+          for tool in clang clang++ llvm-ar llvm-nm llvm-ranlib llvm-objcopy llvm-cov llvm-symbolizer lld ld.lld; do
+            sudo update-alternatives --install /usr/bin/${tool} ${tool} /usr/bin/${tool}-21 100
+          done
+
       - uses: actions/cache@v4
         with:
           path: .ccache
@@ -120,7 +117,6 @@ jobs:
             | tee -a "$GITHUB_STEP_SUMMARY"
 
   release:
-    needs: build-image
     strategy:
       fail-fast: false
       matrix:
@@ -130,14 +126,31 @@ jobs:
           - runner: ubuntu-latest-arm64
             arch: arm64
     runs-on: ${{ matrix.runner }}
-    container:
-      image: git.weaselab.dev/weaselab/conflict-set-ci:latest-${{ matrix.arch }}
-      credentials:
-        username: ${{ secrets.REGISTRY_USER }}
-        password: ${{ secrets.REGISTRY_TOKEN }}
     steps:
       - uses: actions/checkout@v4
 
+      - uses: actions/cache@v4
+        with:
+          path: /var/cache/apt/archives
+          key: apt-${{ matrix.arch }}-${{ hashFiles('.gitea/workflows/ci.yml') }}
+
+      - name: Install dependencies
+        run: |
+          . /etc/os-release
+          wget -qO- https://apt.llvm.org/llvm-snapshot.gpg.key | sudo tee /etc/apt/trusted.gpg.d/apt.llvm.org.asc
+          echo "deb http://apt.llvm.org/${VERSION_CODENAME}/ llvm-toolchain-${VERSION_CODENAME}-21 main" | sudo tee /etc/apt/sources.list.d/llvm.list
+          sudo apt-get update -qq
+          sudo apt-get install -y \
+            biber build-essential ccache clang-21 cmake devscripts \
+            latexmk libc6-dbg llvm-21 lld-21 mold ninja-build rpm \
+            texlive-bibtex-extra texlive-fonts-recommended \
+            texlive-latex-extra texlive-pictures valgrind zstd
+          sudo curl -Ls "https://dl.min.io/client/mc/release/linux-$(dpkg --print-architecture)/mc" \
+            -o /usr/local/bin/mc && sudo chmod +x /usr/local/bin/mc
+          for tool in clang clang++ llvm-ar llvm-nm llvm-ranlib llvm-objcopy llvm-cov llvm-symbolizer lld ld.lld; do
+            sudo update-alternatives --install /usr/bin/${tool} ${tool} /usr/bin/${tool}-21 100
+          done
+
       - uses: actions/cache@v4
         with:
           path: .ccache
@@ -188,9 +201,6 @@ jobs:
           dest="minio/jenkins/conflict-set/${{ gitea.run_number }}/release-${{ matrix.arch }}/"
           zstd build/Testing/*/Test.xml
           mc cp build/Testing/*/Test.xml.zst "$dest"
-          # This step runs even when a previous step failed, to upload test
-          # results. The packages may never have been built though, so skip
-          # them if they're missing.
           if compgen -G "build/*.deb" > /dev/null; then
             mc cp build/*.deb "$dest"
           fi
@@ -209,16 +219,30 @@ jobs:
             | tee -a "$GITHUB_STEP_SUMMARY"
 
   coverage:
-    needs: build-image
     runs-on: ubuntu-latest-amd64
-    container:
-      image: git.weaselab.dev/weaselab/conflict-set-ci:latest-amd64
-      credentials:
-        username: ${{ secrets.REGISTRY_USER }}
-        password: ${{ secrets.REGISTRY_TOKEN }}
     steps:
       - uses: actions/checkout@v4
 
+      - uses: actions/cache@v4
+        with:
+          path: /var/cache/apt/archives
+          key: apt-amd64-${{ hashFiles('.gitea/workflows/ci.yml') }}
+
+      - name: Install dependencies
+        run: |
+          . /etc/os-release
+          wget -qO- https://apt.llvm.org/llvm-snapshot.gpg.key | sudo tee /etc/apt/trusted.gpg.d/apt.llvm.org.asc
+          echo "deb http://apt.llvm.org/${VERSION_CODENAME}/ llvm-toolchain-${VERSION_CODENAME}-21 main" | sudo tee /etc/apt/sources.list.d/llvm.list
+          sudo apt-get update -qq
+          sudo apt-get install -y \
+            build-essential ccache clang-21 cmake gcovr \
+            libc6-dbg llvm-21 lld-21 mold ninja-build python3 valgrind zstd
+          sudo curl -Ls "https://dl.min.io/client/mc/release/linux-amd64/mc" \
+            -o /usr/local/bin/mc && sudo chmod +x /usr/local/bin/mc
+          for tool in clang clang++ llvm-ar llvm-nm llvm-ranlib llvm-objcopy llvm-cov llvm-symbolizer lld ld.lld; do
+            sudo update-alternatives --install /usr/bin/${tool} ${tool} /usr/bin/${tool}-21 100
+          done
+
       - uses: actions/cache@v4
         with:
           path: .ccache

Bench.cpp

@@ -37,15 +37,16 @@ ConflictSet::ReadRange singleton(Arena &arena, TrivialSpan key) {
 }
 
 ConflictSet::ReadRange prefixRange(Arena &arena, TrivialSpan key) {
-  int index;
+  int index = key.size() - 1;
-  for (index = key.size() - 1; index >= 0; index--)
+  for (; index >= 0; index--)
-    if ((key[index]) != 255)
+    if (key[index] != 255)
       break;
 
   // Must not be called with a string that consists only of zero or more '\xff'
-  // bytes.
+  // bytes, or with an empty string (which has no finite upper bound).
   if (index < 0) {
     assert(false);
+    std::abort();
   }
 
   uint8_t *buf = new (arena) uint8_t[index + 1];

CMakeLists.txt

@@ -139,6 +139,7 @@ add_custom_command(
   COMMAND_EXPAND_LISTS)
 
 add_library(${PROJECT_NAME} SHARED ${CMAKE_BINARY_DIR}/${PROJECT_NAME}.o)
+add_dependencies(${PROJECT_NAME} ${PROJECT_NAME}-object)
 set_target_properties(
   ${PROJECT_NAME} PROPERTIES LIBRARY_OUTPUT_DIRECTORY
                              "${CMAKE_CURRENT_BINARY_DIR}/radix_tree")
@@ -155,6 +156,7 @@ if(HAS_VERSION_SCRIPT)
 endif()
 
 add_library(${PROJECT_NAME}-static STATIC ${CMAKE_BINARY_DIR}/${PROJECT_NAME}.o)
+add_dependencies(${PROJECT_NAME}-static ${PROJECT_NAME}-object)
 if(CMAKE_BUILD_TYPE STREQUAL Debug)
   set_target_properties(${PROJECT_NAME}-static PROPERTIES LINKER_LANGUAGE CXX)
 else()
@@ -383,13 +385,25 @@ if(CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR AND BUILD_TESTING)
   if(NOT CMAKE_CROSSCOMPILING)
     find_program(HARDENING_CHECK hardening-check)
     if(HARDENING_CHECK)
+      # Not all versions of hardening-check support the same options, so query
+      # the help output before using architecture-specific skips.
+      execute_process(
+        COMMAND ${HARDENING_CHECK} --help
+        OUTPUT_VARIABLE hardening_check_help
+        ERROR_VARIABLE hardening_check_help
+        OUTPUT_STRIP_TRAILING_WHITESPACE ERROR_STRIP_TRAILING_WHITESPACE)
+      set(hardening_check_arch_flags "")
       # Control flow integrity (CET) is x86-only and branch protection (PAC/BTI)
       # is arm64-only, so ignore whichever doesn't apply.
       if(CMAKE_SYSTEM_PROCESSOR STREQUAL aarch64 OR CMAKE_SYSTEM_PROCESSOR
                                                     STREQUAL arm64)
-        set(hardening_check_arch_flags --nocfprotection)
+        if(hardening_check_help MATCHES "nocfprotection")
+          list(APPEND hardening_check_arch_flags --nocfprotection)
+        endif()
       else()
-        set(hardening_check_arch_flags --nobranchprotection)
+        if(hardening_check_help MATCHES "nobranchprotection")
+          list(APPEND hardening_check_arch_flags --nobranchprotection)
+        endif()
       endif()
       add_test(
         NAME hardening_check

ConflictSet.cpp

@@ -5589,7 +5589,12 @@ ConflictSet::ConflictSet(ConflictSet &&other) noexcept
     : impl(std::exchange(other.impl, nullptr)) {}
 
 ConflictSet &ConflictSet::operator=(ConflictSet &&other) noexcept {
+  if (this != &other) {
+    if (impl) {
+      internal_destroy(impl);
+    }
     impl = std::exchange(other.impl, nullptr);
+  }
   return *this;
 }
 
@@ -5674,13 +5679,13 @@ std::string getPartialKeyPrintable(Node *n) {
 }
 
 std::string strinc(std::string_view str, bool &ok) {
-  int index;
+  int index = static_cast<int>(str.size()) - 1;
-  for (index = str.size() - 1; index >= 0; index--)
+  for (; index >= 0; index--)
-    if ((uint8_t &)(str[index]) != 255)
+    if (static_cast<uint8_t>(str[index]) != 255)
       break;
 
   // Must not be called with a string that consists only of zero or more
-  // '\xff' bytes.
+  // '\xff' bytes, and the empty string has no successor.
   if (index < 0) {
     ok = false;
     return {};
@@ -5688,7 +5693,8 @@ std::string strinc(std::string_view str, bool &ok) {
   ok = true;
 
   auto r = std::string(str.substr(0, index + 1));
-  ((uint8_t &)r[r.size() - 1])++;
+  auto &last = r[r.size() - 1];
+  last = static_cast<char>(static_cast<uint8_t>(last) + 1);
   return r;
 }
 

HashTable.cpp

@@ -96,7 +96,9 @@ void ConflictSet::setOldestVersion(int64_t oldestVersion) {
   return impl->setOldestVersion(oldestVersion);
 }
 
-int64_t ConflictSet::getBytes() const { return -1; }
+// The hash_table implementation does not track memory usage, so return 0 to
+// satisfy the API contract that getBytes() returns a non-negative value.
+int64_t ConflictSet::getBytes() const { return 0; }
 
 void ConflictSet::getMetricsV1(MetricsV1 **metrics, int *count) const {
   *metrics = nullptr;
@@ -119,7 +121,13 @@ ConflictSet::ConflictSet(ConflictSet &&other) noexcept
     : impl(std::exchange(other.impl, nullptr)) {}
 
 ConflictSet &ConflictSet::operator=(ConflictSet &&other) noexcept {
+  if (this != &other) {
+    if (impl) {
+      impl->~Impl();
+      safe_free(impl, sizeof(Impl));
+    }
     impl = std::exchange(other.impl, nullptr);
+  }
   return *this;
 }
 
@@ -155,7 +163,10 @@ __attribute__((__visibility__("default"))) void ConflictSet_destroy(void *cs) {
 }
 __attribute__((__visibility__("default"))) int64_t
 ConflictSet_getBytes(void *cs) {
-  using Impl = ConflictSet::Impl;
+  (void)cs;
-  return -1;
+  // The hash_table implementation does not track memory usage, so return 0 to
+  // satisfy the API contract that ConflictSet_getBytes returns a non-negative
+  // value.
+  return 0;
 }
 }

RealDataBench.cpp

@@ -1,5 +1,6 @@
 #include <ConflictSet.h>
 
+#include <algorithm>
 #include <cerrno>
 #include <chrono>
 #include <cstdio>
@@ -77,10 +78,10 @@ int main(int argc, const char **argv) {
       begin = end + 1;
       end = (uint8_t *)memchr(begin, '\n', size);
 
-      if (line.size() > 0 && line[0] == 'P') {
+      if (line.size() >= 2 && line[0] == 'P') {
-        write = line.subspan(2, line.size());
+        write = line.subspan(2, line.size() - 2);
-      } else if (line.size() > 0 && line[0] == 'L') {
+      } else if (line.size() >= 2 && line[0] == 'L') {
-        reads.push_back(line.subspan(2, line.size()));
+        reads.push_back(line.subspan(2, line.size() - 2));
       } else if (line.empty()) {
         {
           readRanges.resize(reads.size());
@@ -90,7 +91,7 @@ int main(int argc, const char **argv) {
             iter->begin.len = read.size();
             checkBytes += read.size();
             iter->end.len = 0;
-            iter->readVersion = version - 100;
+            iter->readVersion = std::max<int64_t>(0, version - 100);
             ++iter;
           }
         }
@@ -121,7 +122,7 @@ int main(int argc, const char **argv) {
         }
 
         timer = now();
-        cs.setOldestVersion(version - 10000);
+        cs.setOldestVersion(std::max<int64_t>(0, version - 10000));
         gcTime += now() - timer;
       }
     }

ServerBench.cpp

@@ -12,6 +12,7 @@
 #include <sys/ioctl.h>
 #include <sys/resource.h>
 #include <sys/socket.h>
+#include <sys/syscall.h>
 #include <sys/types.h>
 #include <sys/uio.h>
 #include <thread>

SkipList.cpp

@@ -981,7 +981,12 @@ ConflictSet::ConflictSet(ConflictSet &&other) noexcept
     : impl(std::exchange(other.impl, nullptr)) {}
 
 ConflictSet &ConflictSet::operator=(ConflictSet &&other) noexcept {
+  if (this != &other) {
+    if (impl) {
+      internal_destroy(impl);
+    }
     impl = std::exchange(other.impl, nullptr);
+  }
   return *this;
 }
 

conflict_set.py

@@ -27,23 +27,37 @@ class Result(enum.Enum):
     TOO_OLD = 2
 
 
-def write(begin: bytes, end: Optional[bytes] = None) -> WriteRange:
+def _make_key(buf: bytes) -> tuple[_Key, bytearray]:
-    b = (ctypes.c_ubyte * len(begin)).from_buffer(bytearray(begin))
+    """Create a _Key and a backing bytearray that must be kept alive."""
+    backing = bytearray(buf)
+    array = (ctypes.c_ubyte * len(backing)).from_buffer(backing)
+    return _Key(array, len(array)), backing
 
+
+def write(begin: bytes, end: Optional[bytes] = None) -> WriteRange:
+    begin_key, begin_buf = _make_key(begin)
     if end is None:
-        e = (ctypes.c_ubyte * 0)()
+        end_key = _Key((ctypes.c_ubyte * 0)(), 0)
+        end_buf = None
     else:
-        e = (ctypes.c_ubyte * len(end)).from_buffer(bytearray(end))
+        end_key, end_buf = _make_key(end)
-    return WriteRange(_Key(b, len(b)), _Key(e, len(e)))
+    result = WriteRange(begin_key, end_key)
+    result._begin_buf = begin_buf
+    result._end_buf = end_buf
+    return result
 
 
 def read(version: int, begin: bytes, end: Optional[bytes] = None) -> ReadRange:
-    b = (ctypes.c_ubyte * len(begin)).from_buffer(bytearray(begin))
+    begin_key, begin_buf = _make_key(begin)
     if end is None:
-        e = (ctypes.c_ubyte * 0)()
+        end_key = _Key((ctypes.c_ubyte * 0)(), 0)
+        end_buf = None
     else:
-        e = (ctypes.c_ubyte * len(end)).from_buffer(bytearray(end))
+        end_key, end_buf = _make_key(end)
-    return ReadRange(_Key(b, len(b)), _Key(e, len(e)), version)
+    result = ReadRange(begin_key, end_key, version)
+    result._begin_buf = begin_buf
+    result._end_buf = end_buf
+    return result
 
 
 class ConflictSet:
@@ -88,6 +102,7 @@ class ConflictSet:
             ctypes.POINTER(ctypes.c_int),
             ctypes.c_int,
         )
+        self._lib.ConflictSet_check.restype = None
 
         self._lib.ConflictSet_addWrites.argtypes = (
             ctypes.c_void_p,
@@ -95,13 +110,16 @@ class ConflictSet:
             ctypes.c_int,
             ctypes.c_int64,
         )
+        self._lib.ConflictSet_addWrites.restype = None
 
         self._lib.ConflictSet_setOldestVersion.argtypes = (
             ctypes.c_void_p,
             ctypes.c_int64,
         )
+        self._lib.ConflictSet_setOldestVersion.restype = None
 
         self._lib.ConflictSet_destroy.argtypes = (ctypes.c_void_p,)
+        self._lib.ConflictSet_destroy.restype = None
 
         self._lib.ConflictSet_getBytes.argtypes = (ctypes.c_void_p,)
         self._lib.ConflictSet_getBytes.restype = ctypes.c_int64

include/ConflictSet.h

@@ -88,7 +88,8 @@ struct __attribute__((__visibility__("default"))) ConflictSet {
 
   ~ConflictSet();
 
-  /** Returns the total bytes in use by this ConflictSet */
+  /** Returns the total bytes in use by this ConflictSet. Implementations that
+   * do not track memory usage return 0. */
   int64_t getBytes() const;
 
   /** Experimental! */
@@ -132,6 +133,13 @@ struct __attribute__((__visibility__("default"))) ConflictSet {
 
 private:
   Impl *impl;
+#if __cplusplus <= 199711L
+  /* Declared private and left undefined to prevent copying in C++98/C++03.
+     The compiler would otherwise implicitly generate public copy operations,
+     which share the opaque Impl* and cause a double-free. */
+  ConflictSet(const ConflictSet &);
+  ConflictSet &operator=(const ConflictSet &);
+#endif
 };
 } /* namespace weaselab */
 
@@ -211,7 +219,8 @@ ConflictSet *ConflictSet_create(int64_t oldestVersion);
 
 void ConflictSet_destroy(ConflictSet *cs);
 
-/** Returns the total bytes in use by this ConflictSet */
+/** Returns the total bytes in use by this ConflictSet. Implementations that
+ * do not track memory usage return 0. */
 int64_t ConflictSet_getBytes(const ConflictSet *cs);
 
 #endif

test_conflict_set.py

@@ -57,6 +57,53 @@ def test_conflict_set():
         assert cs.check(read(0, key), read(1, key)) == [Result.TOO_OLD, Result.COMMIT]
 
 
+def test_hash_table_getBytes():
+    # Regression test for issue #62: the hash_table implementation is
+    # point-query only and does not track memory usage, but getBytes() must
+    # still return a non-negative value rather than -1.
+    with ConflictSet(0, build_dir=build_dir, implementation="hash_table") as cs:
+        assert cs.getBytes() == 0
+        cs.addWrites(1, write(b"key"))
+        assert cs.getBytes() >= 0
+        assert cs.check(read(0, b"key")) == [Result.CONFLICT]
+
+
+def test_write_read_without_outer_reference():
+    # Regression test for issue #42: WriteRange/ReadRange must keep their
+    # backing key buffers alive, because the C library reads the pointer
+    # stored in _Key while addWrites/check run.
+    with DebugConflictSet() as cs:
+        # The bytes literal is not referenced after this expression.
+        cs.addWrites(1, write(b"key"))
+        assert cs.check(read(0, b"key")) == [Result.CONFLICT]
+
+        cs.addWrites(2, write(b"a", b"z"))
+        assert cs.check(read(1, b"a", b"z")) == [Result.CONFLICT]
+        assert cs.check(read(1, b"b")) == [Result.CONFLICT]
+        assert cs.check(read(1, b"0")) == [Result.COMMIT]
+
+
+def test_range_keeps_key_buffers_alive():
+    # Verify the fix for issue #42: returned range objects must retain a
+    # reference to the backing bytearray so the C pointer stays valid after
+    # the helper returns.
+    w = write(b"key")
+    assert w._begin_buf == bytearray(b"key")
+    assert w._end_buf is None
+
+    w2 = write(b"a", b"z")
+    assert w2._begin_buf == bytearray(b"a")
+    assert w2._end_buf == bytearray(b"z")
+
+    r = read(0, b"key")
+    assert r._begin_buf == bytearray(b"key")
+    assert r._end_buf is None
+
+    r2 = read(1, b"a", b"z")
+    assert r2._begin_buf == bytearray(b"a")
+    assert r2._end_buf == bytearray(b"z")
+
+
 def test_update_zero_should_commit():
     with DebugConflictSet() as cs1:
         with DebugConflictSet() as cs2:
@@ -68,7 +115,7 @@ def test_update_zero_should_commit():
             for i in range(256 - 17, 256):
                 cs2.addWrites(int(1), write(bytes([i])))
             # Scan until first point write
-            cs2.check(read(0, b"\x00", bytes([256 - 17])))
+            assert cs2.check(read(0, b"\x00", bytes([256 - 17]))) == [Result.COMMIT]
 
 
 def test_update_zero_should_conflict():
@@ -81,7 +128,7 @@ def test_update_zero_should_conflict():
             # "zero" is now 2**31 + 100
             cs1.addWrites(2**32 + 101, write(b"", b"\x02"), write(b"\x01"))
             # rangeVersion of \x01 is now 2**31 + 100 ("max" of (2**31 + 100, 2**32 + 101))
-            cs1.check(read(2**32 + 1, b"\x00"))
+            assert cs1.check(read(2**32 + 1, b"\x00")) == [Result.CONFLICT]
             # but 2**32 + 1 ">" 2**31 + 100 , and it incorrectly commits