WIP

.pre-commit-config.yaml

@@ -24,6 +24,14 @@ repos:
         entry: "^#define SHOW_MEMORY 1$"
         language: pygrep
         types: [c++]
+  - repo: local
+    hooks:
+      - id: sim cache misses check
+        name: disallow checking in SIM_CACHE_MISSES=1
+        description: disallow checking in SIM_CACHE_MISSES=1
+        entry: "^#define SIM_CACHE_MISSES 1$"
+        language: pygrep
+        types: [c++]
   - repo: https://github.com/shellcheck-py/shellcheck-py
     rev: a23f6b85d0fdd5bb9d564e2579e678033debbdff # frozen: v0.10.0.1
     hooks:

Bench.cpp

@@ -7,7 +7,6 @@
 void showMemory(const ConflictSet &cs);
 #endif
 
-#define ANKERL_NANOBENCH_IMPLEMENT
 #include "third_party/nanobench.h"
 
 constexpr int kNumKeys = 1000000;

CMakeLists.txt

@@ -1,7 +1,7 @@
 cmake_minimum_required(VERSION 3.18)
 project(
   conflict-set
-  VERSION 0.0.13
+  VERSION 0.0.14
   DESCRIPTION
     "A data structure for optimistic concurrency control on ranges of bitwise-lexicographically-ordered keys."
   HOMEPAGE_URL "https://git.weaselab.dev/weaselab/conflict-set"
@@ -72,12 +72,6 @@ else()
   add_link_options(-Wl,--gc-sections)
 endif()
 
-if(EMSCRIPTEN)
-  # https://github.com/emscripten-core/emscripten/issues/15377#issuecomment-1285167486
-  add_link_options(-lnodefs.js -lnoderawfs.js)
-  add_link_options(-s ALLOW_MEMORY_GROWTH)
-endif()
-
 if(NOT USE_SIMD_FALLBACK)
   cmake_push_check_state()
   list(APPEND CMAKE_REQUIRED_FLAGS -mavx)
@@ -144,6 +138,8 @@ include(CTest)
 # disable tests if this is being used through e.g. FetchContent
 if(CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR AND BUILD_TESTING)
 
+  add_library(nanobench ${CMAKE_CURRENT_SOURCE_DIR}/nanobench.cpp)
+
   set(TEST_FLAGS -Wall -Wextra -Wunreachable-code -Wpedantic -UNDEBUG)
 
   # corpus tests, which are tests curated by libfuzzer. The goal is to get broad
@@ -191,6 +187,7 @@ if(CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR AND BUILD_TESTING)
   target_include_directories(conflict_set_main
                              PRIVATE ${CMAKE_CURRENT_SOURCE_DIR}/include)
   target_compile_definitions(conflict_set_main PRIVATE ENABLE_MAIN)
+  target_link_libraries(conflict_set_main PRIVATE nanobench)
 
   if(NOT APPLE)
     # libfuzzer target, to generate/manage corpus
@@ -336,7 +333,7 @@ if(CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR AND BUILD_TESTING)
 
   # bench
   add_executable(conflict_set_bench Bench.cpp)
-  target_link_libraries(conflict_set_bench PRIVATE ${PROJECT_NAME})
+  target_link_libraries(conflict_set_bench PRIVATE ${PROJECT_NAME} nanobench)
   set_target_properties(conflict_set_bench PROPERTIES SKIP_BUILD_RPATH ON)
   add_executable(real_data_bench RealDataBench.cpp)
   target_link_libraries(real_data_bench PRIVATE ${PROJECT_NAME})
@@ -351,6 +348,14 @@ if(CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR AND BUILD_TESTING)
   add_executable(server_bench ServerBench.cpp)
   target_link_libraries(server_bench PRIVATE ${PROJECT_NAME})
   set_target_properties(server_bench PROPERTIES SKIP_BUILD_RPATH ON)
+
+  add_executable(interleaving_test InterleavingTest.cpp)
+  # work around lack of musttail for gcc
+  if(CMAKE_CXX_COMPILER_ID STREQUAL "GNU" AND CMAKE_BUILD_TYPE STREQUAL "Debug")
+    target_compile_options(interleaving_test PRIVATE -Og
+                                                     -foptimize-sibling-calls)
+  endif()
+  target_link_libraries(interleaving_test PRIVATE nanobench)
 endif()
 
 # packaging

ConflictSet.cpp

@@ -17,9 +17,9 @@ limitations under the License.
 #include "ConflictSet.h"
 #include "Internal.h"
 #include "LongestCommonPrefix.h"
+#include "Metrics.h"
 
 #include <algorithm>
-#include <atomic>
 #include <bit>
 #include <cassert>
 #include <cstddef>
@@ -48,6 +48,17 @@ limitations under the License.
 #endif
 #endif
 
+#define SIM_CACHE_MISSES 0
+#if SIM_CACHE_MISSES
+constexpr void simCacheMiss(void *x) {
+  if (x) {
+    _mm_clflush(x);
+  }
+}
+#else
+constexpr void simCacheMiss(void *) {}
+#endif
+
 #include <memcheck.h>
 
 using namespace weaselab;
@@ -578,39 +589,6 @@ static_assert(kBytesPerKey - sizeof(Node0) >= kMinNodeSurplus);
 
 constexpr int64_t kFreeListMaxMemory = 1 << 20;
 
-struct Metric {
-  Metric *prev;
-  const char *name;
-  const char *help;
-  ConflictSet::MetricsV1::Type type;
-  std::atomic<int64_t> value;
-
-protected:
-  Metric(ConflictSet::Impl *impl, const char *name, const char *help,
-         ConflictSet::MetricsV1::Type type);
-};
-
-struct Gauge : private Metric {
-  Gauge(ConflictSet::Impl *impl, const char *name, const char *help)
-      : Metric(impl, name, help, ConflictSet::MetricsV1::Gauge) {}
-
-  void set(int64_t value) {
-    this->value.store(value, std::memory_order_relaxed);
-  }
-};
-
-struct Counter : private Metric {
-  Counter(ConflictSet::Impl *impl, const char *name, const char *help)
-      : Metric(impl, name, help, ConflictSet::MetricsV1::Counter) {}
-  // Expensive. Accumulate locally and then call add instead of repeatedly
-  // calling add.
-  void add(int64_t value) {
-    assert(value >= 0);
-    static_assert(std::atomic<int64_t>::is_always_lock_free);
-    this->value.fetch_add(value, std::memory_order_relaxed);
-  }
-};
-
 template <class T> struct BoundedFreeListAllocator {
 
   static_assert(sizeof(T) >= sizeof(void *));
@@ -869,21 +847,29 @@ int getNodeIndex(Node16 *self, uint8_t index) {
 
 // Precondition - an entry for index must exist in the node
 Node *&getChildExists(Node3 *self, uint8_t index) {
-  return self->children[getNodeIndex(self, index)];
+  auto &result = self->children[getNodeIndex(self, index)];
+  simCacheMiss(result);
+  return result;
 }
 // Precondition - an entry for index must exist in the node
 Node *&getChildExists(Node16 *self, uint8_t index) {
-  return self->children[getNodeIndex(self, index)];
+  auto &result = self->children[getNodeIndex(self, index)];
+  simCacheMiss(result);
+  return result;
 }
 // Precondition - an entry for index must exist in the node
 Node *&getChildExists(Node48 *self, uint8_t index) {
   assert(self->bitSet.test(index));
-  return self->children[self->index[index]];
+  auto &result = self->children[self->index[index]];
+  simCacheMiss(result);
+  return result;
 }
 // Precondition - an entry for index must exist in the node
 Node *&getChildExists(Node256 *self, uint8_t index) {
   assert(self->bitSet.test(index));
-  return self->children[index];
+  auto &result = self->children[index];
+  simCacheMiss(result);
+  return result;
 }
 
 // Precondition - an entry for index must exist in the node
@@ -1063,6 +1049,7 @@ ChildAndMaxVersion getChildAndMaxVersion(Node3 *self, uint8_t index) {
   if (i < 0) {
     return {};
   }
+  simCacheMiss(self->children[i]);
   return {self->children[i], self->childMaxVersion[i]};
 }
 ChildAndMaxVersion getChildAndMaxVersion(Node16 *self, uint8_t index) {
@@ -1070,6 +1057,7 @@ ChildAndMaxVersion getChildAndMaxVersion(Node16 *self, uint8_t index) {
   if (i < 0) {
     return {};
   }
+  simCacheMiss(self->children[i]);
   return {self->children[i], self->childMaxVersion[i]};
 }
 ChildAndMaxVersion getChildAndMaxVersion(Node48 *self, uint8_t index) {
@@ -1077,9 +1065,11 @@ ChildAndMaxVersion getChildAndMaxVersion(Node48 *self, uint8_t index) {
   if (i < 0) {
     return {};
   }
+  simCacheMiss(self->children[i]);
   return {self->children[i], self->childMaxVersion[i]};
 }
 ChildAndMaxVersion getChildAndMaxVersion(Node256 *self, uint8_t index) {
+  simCacheMiss(self->children[index]);
   return {self->children[index], self->childMaxVersion[index]};
 }
 
@@ -1105,6 +1095,7 @@ Node *getChildGeq(Node0 *, int) { return nullptr; }
 Node *getChildGeq(Node3 *n, int child) {
   for (int i = 0; i < n->numChildren; ++i) {
     if (n->index[i] >= child) {
+      simCacheMiss(n->children[i]);
       return n->children[i];
     }
   }
@@ -1123,7 +1114,10 @@ Node *getChildGeq(Node16 *self, int child) {
   __m128i results = _mm_cmpeq_epi8(key_vec, _mm_min_epu8(key_vec, indices));
   int mask = (1 << self->numChildren) - 1;
   uint32_t bitfield = _mm_movemask_epi8(results) & mask;
-  return bitfield == 0 ? nullptr : self->children[std::countr_zero(bitfield)];
+  auto *result =
+      bitfield == 0 ? nullptr : self->children[std::countr_zero(bitfield)];
+  simCacheMiss(result);
+  return result;
 #elif defined(HAS_ARM_NEON)
   uint8x16_t indices;
   memcpy(&indices, self->index, sizeof(self->index));
@@ -1159,13 +1153,16 @@ Node *getChildGeq(Node48 *self, int child) {
   if (c < 0) {
     return nullptr;
   }
-  return self->children[self->index[c]];
+  auto *result = self->children[self->index[c]];
+  simCacheMiss(result);
+  return result;
 }
 Node *getChildGeq(Node256 *self, int child) {
   int c = self->bitSet.firstSetGeq(child);
   if (c < 0) {
     return nullptr;
   }
+  simCacheMiss(self->children[c]);
   return self->children[c];
 }
 
@@ -1189,20 +1186,26 @@ Node *getChildGeq(Node *self, int child) {
 // Precondition: self has a child
 Node *getFirstChildExists(Node3 *self) {
   assert(self->numChildren > 0);
+  simCacheMiss(self->children[0]);
   return self->children[0];
 }
 // Precondition: self has a child
 Node *getFirstChildExists(Node16 *self) {
   assert(self->numChildren > 0);
+  simCacheMiss(self->children[0]);
   return self->children[0];
 }
 // Precondition: self has a child
 Node *getFirstChildExists(Node48 *self) {
-  return self->children[self->index[self->bitSet.firstSetGeq(0)]];
+  auto *result = self->children[self->index[self->bitSet.firstSetGeq(0)]];
+  simCacheMiss(result);
+  return result;
 }
 // Precondition: self has a child
 Node *getFirstChildExists(Node256 *self) {
-  return self->children[self->bitSet.firstSetGeq(0)];
+  auto *result = self->children[self->bitSet.firstSetGeq(0)];
+  simCacheMiss(result);
+  return result;
 }
 
 // Precondition: self has a child
@@ -2543,38 +2546,19 @@ downLeftSpine:
 namespace {
 // Return true if the max version among all keys that start with key[:prefixLen]
 // that are >= key is <= readVersion
-struct CheckRangeLeftSide {
+bool checkRangeLeftSide(Node *n, std::span<const uint8_t> key, int prefixLen,
-  CheckRangeLeftSide(Node *n, std::span<const uint8_t> key, int prefixLen,
+                        InternalVersionT readVersion, ReadContext *tls) {
-                     InternalVersionT readVersion, ReadContext *tls)
+  auto remaining = key;
-      : n(n), remaining(key), prefixLen(prefixLen), readVersion(readVersion),
-        impl(tls->impl), tls(tls) {
-#if DEBUG_VERBOSE && !defined(NDEBUG)
-    fprintf(stderr, "Check range left side from %s for keys starting with %s\n",
-            printable(key).c_str(),
-            printable(key.subspan(0, prefixLen)).c_str());
-#endif
-  }
-
-  Node *n;
-  std::span<const uint8_t> remaining;
-  int prefixLen;
-  InternalVersionT readVersion;
-  ConflictSet::Impl *impl;
-  ReadContext *tls;
   int searchPathLen = 0;
-  bool ok;
+  for (;; ++tls->range_read_iterations_accum) {
-
-  bool step() {
     if (remaining.size() == 0) {
       assert(searchPathLen >= prefixLen);
-      ok = maxVersion(n) <= readVersion;
+      return maxVersion(n) <= readVersion;
-      return true;
     }
 
     if (searchPathLen >= prefixLen) {
       if (!checkMaxBetweenExclusive(n, remaining[0], 256, readVersion, tls)) {
-        ok = false;
+        return false;
-        return true;
       }
     }
 
@@ -2584,18 +2568,16 @@ struct CheckRangeLeftSide {
       if (c != nullptr) {
         if (searchPathLen < prefixLen) {
           n = c;
-          return downLeftSpine();
+          goto downLeftSpine;
         }
         n = c;
-        ok = maxVersion(n) <= readVersion;
+        return maxVersion(n) <= readVersion;
-        return true;
       } else {
         n = nextSibling(n);
         if (n == nullptr) {
-          ok = true;
           return true;
         }
-        return downLeftSpine();
+        goto downLeftSpine;
       }
     }
 
@@ -2611,21 +2593,18 @@ struct CheckRangeLeftSide {
         auto c = n->partialKey()[i] <=> remaining[i];
         if (c > 0) {
           if (searchPathLen < prefixLen) {
-            return downLeftSpine();
+            goto downLeftSpine;
           }
           if (n->entryPresent && n->entry.rangeVersion > readVersion) {
-            ok = false;
+            return false;
-            return true;
           }
-          ok = maxVersion(n) <= readVersion;
+          return maxVersion(n) <= readVersion;
-          return true;
         } else {
           n = nextSibling(n);
           if (n == nullptr) {
-            ok = true;
             return true;
           }
-          return downLeftSpine();
+          goto downLeftSpine;
         }
       }
       if (commonLen == n->partialKeyLen) {
@@ -2634,83 +2613,47 @@ struct CheckRangeLeftSide {
       } else if (n->partialKeyLen > int(remaining.size())) {
         assert(searchPathLen >= prefixLen);
         if (n->entryPresent && n->entry.rangeVersion > readVersion) {
-          ok = false;
+          return false;
-          return true;
         }
-        ok = maxVersion(n) <= readVersion;
+        return maxVersion(n) <= readVersion;
-        return true;
       }
     }
     if (maxV <= readVersion) {
-      ok = true;
       return true;
     }
-    return false;
   }
-
+downLeftSpine:
-  bool downLeftSpine() {
+  for (; !n->entryPresent; n = getFirstChildExists(n)) {
-    for (; !n->entryPresent; n = getFirstChildExists(n)) {
-    }
-    ok = n->entry.rangeVersion <= readVersion;
-    return true;
   }
-};
+  return n->entry.rangeVersion <= readVersion;
+}
 
 // Return true if the max version among all keys that start with key[:prefixLen]
 // that are < key is <= readVersion
-struct CheckRangeRightSide {
+bool checkRangeRightSide(Node *n, std::span<const uint8_t> key, int prefixLen,
-  CheckRangeRightSide(Node *n, std::span<const uint8_t> key, int prefixLen,
+                         InternalVersionT readVersion, ReadContext *tls) {
-                      InternalVersionT readVersion, ReadContext *tls)
+  auto remaining = key;
-      : n(n), key(key), remaining(key), prefixLen(prefixLen),
-        readVersion(readVersion), impl(tls->impl), tls(tls) {
-#if DEBUG_VERBOSE && !defined(NDEBUG)
-    fprintf(stderr, "Check range right side to %s for keys starting with %s\n",
-            printable(key).c_str(),
-            printable(key.subspan(0, prefixLen)).c_str());
-#endif
-  }
-
-  Node *n;
-  std::span<const uint8_t> key;
-  std::span<const uint8_t> remaining;
-  int prefixLen;
-  InternalVersionT readVersion;
-  ConflictSet::Impl *impl;
-  ReadContext *tls;
   int searchPathLen = 0;
-  bool ok;
-
-  bool step() {
-#if DEBUG_VERBOSE && !defined(NDEBUG)
-    fprintf(stderr,
-            "Search path: %s, searchPathLen: %d, prefixLen: %d, remaining: "
-            "%s\n",
-            getSearchPathPrintable(n).c_str(), searchPathLen, prefixLen,
-            printable(remaining).c_str());
-#endif
 
+  for (;; ++tls->range_read_iterations_accum) {
     assert(searchPathLen <= int(key.size()));
-
     if (remaining.size() == 0) {
-      return downLeftSpine();
+      goto downLeftSpine;
     }
 
     if (searchPathLen >= prefixLen) {
       if (n->entryPresent && n->entry.pointVersion > readVersion) {
-        ok = false;
+        return false;
-        return true;
       }
 
       if (!checkMaxBetweenExclusive(n, -1, remaining[0], readVersion, tls)) {
-        ok = false;
+        return false;
-        return true;
       }
     }
 
     if (searchPathLen > prefixLen && n->entryPresent &&
         n->entry.rangeVersion > readVersion) {
-      ok = false;
+      return false;
-      return true;
     }
 
     auto *child = getChild(n, remaining[0]);
@@ -2718,9 +2661,9 @@ struct CheckRangeRightSide {
       auto c = getChildGeq(n, remaining[0]);
       if (c != nullptr) {
         n = c;
-        return downLeftSpine();
+        goto downLeftSpine;
       } else {
-        return backtrack();
+        goto backtrack;
       }
     }
 
@@ -2736,57 +2679,48 @@ struct CheckRangeRightSide {
         ++searchPathLen;
         auto c = n->partialKey()[i] <=> remaining[i];
         if (c > 0) {
-          return downLeftSpine();
+          goto downLeftSpine;
         } else {
           if (searchPathLen > prefixLen && n->entryPresent &&
               n->entry.rangeVersion > readVersion) {
-            ok = false;
+            return false;
-            return true;
           }
-          return backtrack();
+          goto backtrack;
         }
       }
       if (commonLen == n->partialKeyLen) {
         // partial key matches
         remaining = remaining.subspan(commonLen, remaining.size() - commonLen);
       } else if (n->partialKeyLen > int(remaining.size())) {
-        return downLeftSpine();
+        goto downLeftSpine;
-      }
-    }
-    return false;
-  }
-
-  bool backtrack() {
-    for (;;) {
-      // searchPathLen > prefixLen implies n is not the root
-      if (searchPathLen > prefixLen && maxVersion(n) > readVersion) {
-        ok = false;
-        return true;
-      }
-      if (n->parent == nullptr) {
-        ok = true;
-        return true;
-      }
-      auto next = getChildGeq(n->parent, n->parentsIndex + 1);
-      if (next == nullptr) {
-        searchPathLen -= 1 + n->partialKeyLen;
-        n = n->parent;
-      } else {
-        searchPathLen -= n->partialKeyLen;
-        n = next;
-        searchPathLen += n->partialKeyLen;
-        return downLeftSpine();
       }
     }
   }
-
+backtrack:
-  bool downLeftSpine() {
+  for (;;) {
-    for (; !n->entryPresent; n = getFirstChildExists(n)) {
+    // searchPathLen > prefixLen implies n is not the root
+    if (searchPathLen > prefixLen && maxVersion(n) > readVersion) {
+      return false;
+    }
+    if (n->parent == nullptr) {
+      return true;
+    }
+    auto next = getChildGeq(n->parent, n->parentsIndex + 1);
+    if (next == nullptr) {
+      searchPathLen -= 1 + n->partialKeyLen;
+      n = n->parent;
+    } else {
+      searchPathLen -= n->partialKeyLen;
+      n = next;
+      searchPathLen += n->partialKeyLen;
+      goto downLeftSpine;
     }
-    ok = n->entry.rangeVersion <= readVersion;
-    return true;
   }
-};
+downLeftSpine:
+  for (; !n->entryPresent; n = getFirstChildExists(n)) {
+  }
+  return n->entry.rangeVersion <= readVersion;
+}
 } // namespace
 
 bool checkRangeRead(Node *n, std::span<const uint8_t> begin,
@@ -2807,8 +2741,8 @@ bool checkRangeRead(Node *n, std::span<const uint8_t> begin,
 
   auto remaining = begin.subspan(0, lcp);
   Arena arena;
-  // If the common prefix isn't a prefix of any physical entry in the tree, we
+
-  // can go to "downLeftSpine"
+  // Advance down common prefix, but stay on a physical path in the tree
   for (;; ++tls->range_read_iterations_accum) {
     assert(getSearchPath(arena, n) <=>
                begin.subspan(0, lcp - remaining.size()) ==
@@ -2849,47 +2783,17 @@ bool checkRangeRead(Node *n, std::span<const uint8_t> begin,
   lcp -= consumed;
 
   if (lcp == int(begin.size())) {
-    CheckRangeRightSide checkRangeRightSide{n, end, lcp, readVersion, tls};
+    return checkRangeRightSide(n, end, lcp, readVersion, tls);
-    while (!checkRangeRightSide.step())
-      ;
-    return checkRangeRightSide.ok;
   }
 
-  if (!checkRangeStartsWith(n, begin.subspan(0, lcp), begin[lcp], end[lcp],
+  // This makes it safe to check maxVersion within checkRangeLeftSide. If this
-                            readVersion, tls)) {
-    return false;
-  }
-
-  // This makes it safe to check maxVersion within CheckRangeLeftSide. If this
   // were false, then we would have returned above since lcp == begin.size().
   assert(!(n->parent == nullptr && begin.size() == 0));
-  CheckRangeLeftSide checkRangeLeftSide{n, begin, lcp + 1, readVersion, tls};
-  CheckRangeRightSide checkRangeRightSide{n, end, lcp + 1, readVersion, tls};
 
-  for (;;) {
+  return checkRangeStartsWith(n, begin.subspan(0, lcp), begin[lcp], end[lcp],
-    bool leftDone = checkRangeLeftSide.step();
+                              readVersion, tls) &&
-    bool rightDone = checkRangeRightSide.step();
+         checkRangeLeftSide(n, begin, lcp + 1, readVersion, tls) &&
-    if (!leftDone && !rightDone) {
+         checkRangeRightSide(n, end, lcp + 1, readVersion, tls);
-      tls->range_read_iterations_accum += 2;
-      continue;
-    }
-    if (leftDone && rightDone) {
-      break;
-    } else if (leftDone) {
-      while (!checkRangeRightSide.step()) {
-        ++tls->range_read_iterations_accum;
-      }
-      break;
-    } else {
-      assert(rightDone);
-      while (!checkRangeLeftSide.step()) {
-        ++tls->range_read_iterations_accum;
-      }
-    }
-    break;
-  }
-
-  return checkRangeLeftSide.ok && checkRangeRightSide.ok;
 }
 
 #ifdef __x86_64__
@@ -3141,34 +3045,288 @@ Node *firstGeqPhysical(Node *n, const std::span<const uint8_t> key) {
   }
 }
 
+#ifndef __has_attribute
+#define __has_attribute(x) 0
+#endif
+
+#if __has_attribute(musttail)
+#define MUSTTAIL __attribute__((musttail))
+#else
+#define MUSTTAIL
+#endif
+
+#if __has_attribute(preserve_none)
+#define CONTINUATION_CALLING_CONVENTION __attribute__((preserve_none))
+#else
+#define CONTINUATION_CALLING_CONVENTION
+#endif
+
+typedef CONTINUATION_CALLING_CONVENTION void (*continuation)(struct CheckAll *,
+                                                             int64_t prevJob,
+                                                             int64_t job,
+                                                             int64_t started,
+                                                             int64_t count);
+
+// State relevant to a particular query
+struct CheckJob {
+  void setResult(bool ok) {
+    *result = ok ? ConflictSet::Commit : ConflictSet::Conflict;
+  }
+
+  [[nodiscard]] continuation init(const ConflictSet::ReadRange *read,
+                                  ConflictSet::Result *result, Node *root,
+                                  int64_t oldestVersionFullPrecision,
+                                  ReadContext *tls);
+
+  Node *n;
+  ChildAndMaxVersion childAndVersion;
+  std::span<const uint8_t> begin;
+  InternalVersionT readVersion;
+  ConflictSet::Result *result;
+};
+
+// State relevant to all queries
+struct CheckAll {
+  constexpr static int kConcurrent = 32;
+  const ConflictSet::ReadRange *queries;
+  ConflictSet::Result *results;
+  CheckJob inProgress[kConcurrent];
+  continuation next[kConcurrent];
+  int nextJob[kConcurrent];
+  Node *root;
+  int64_t oldestVersionFullPrecision;
+  ReadContext *tls;
+};
+
+CONTINUATION_CALLING_CONVENTION void keepGoing(CheckAll *context,
+                                               int64_t prevJob, int64_t job,
+                                               int64_t started, int64_t count) {
+  prevJob = job;
+  job = context->nextJob[job];
+  MUSTTAIL return context->next[job](context, prevJob, job, started, count);
+}
+
+CONTINUATION_CALLING_CONVENTION void complete(CheckAll *context,
+                                              int64_t prevJob, int64_t job,
+                                              int64_t started, int64_t count) {
+  if (started == count) {
+    if (prevJob == job) {
+      return;
+    }
+    context->nextJob[prevJob] = context->nextJob[job];
+    job = prevJob;
+  } else {
+    int temp = started++;
+    context->next[job] = context->inProgress[job].init(
+        context->queries + temp, context->results + temp, context->root,
+        context->oldestVersionFullPrecision, context->tls);
+  }
+  MUSTTAIL return keepGoing(context, prevJob, job, started, count);
+}
+
+namespace check_point_read_state_machine {
+
+CONTINUATION_CALLING_CONVENTION void
+down_left_spine(struct CheckAll *, int64_t prevJob, int64_t job,
+                int64_t started, int64_t count);
+CONTINUATION_CALLING_CONVENTION void iter(struct CheckAll *, int64_t prevJob,
+                                          int64_t job, int64_t started,
+                                          int64_t count);
+CONTINUATION_CALLING_CONVENTION void begin(struct CheckAll *, int64_t prevJob,
+                                           int64_t job, int64_t started,
+                                           int64_t count);
+
+void begin(struct CheckAll *context, int64_t prevJob, int64_t job,
+           int64_t started, int64_t count) {
+  ++context->tls->point_read_accum;
+#if DEBUG_VERBOSE && !defined(NDEBUG)
+  fprintf(stderr, "Check point read: %s\n", printable(key).c_str());
+#endif
+  auto *j = context->inProgress + job;
+
+  if (j->begin.size() == 0) {
+    if (j->n->entryPresent) {
+      j->setResult(j->n->entry.pointVersion <= j->readVersion);
+      MUSTTAIL return complete(context, prevJob, job, started, count);
+    }
+    j->n = getFirstChildExists(j->n);
+    context->next[job] = down_left_spine;
+    __builtin_prefetch(j->n);
+    MUSTTAIL return keepGoing(context, prevJob, job, started, count);
+  }
+
+  j->childAndVersion = getChildAndMaxVersion(j->n, j->begin[0]);
+  context->next[job] = iter;
+  __builtin_prefetch(j->childAndVersion.child);
+  MUSTTAIL return keepGoing(context, prevJob, job, started, count);
+}
+
+void iter(struct CheckAll *context, int64_t prevJob, int64_t job,
+          int64_t started, int64_t count) {
+  auto *j = context->inProgress + job;
+  if (j->childAndVersion.child == nullptr) {
+    auto c = getChildGeq(j->n, j->begin[0]);
+    if (c != nullptr) {
+      j->n = c;
+      context->next[job] = down_left_spine;
+      __builtin_prefetch(j->n);
+      MUSTTAIL return keepGoing(context, prevJob, job, started, count);
+    } else {
+      j->n = nextSibling(j->n);
+      if (j->n == nullptr) {
+        j->setResult(true);
+        MUSTTAIL return complete(context, prevJob, job, started, count);
+      }
+      context->next[job] = down_left_spine;
+      __builtin_prefetch(j->n);
+      MUSTTAIL return keepGoing(context, prevJob, job, started, count);
+    }
+  }
+
+  j->n = j->childAndVersion.child;
+  j->begin = j->begin.subspan(1, j->begin.size() - 1);
+
+  if (j->n->partialKeyLen > 0) {
+    int commonLen = std::min<int>(j->n->partialKeyLen, j->begin.size());
+    int i = longestCommonPrefix(j->n->partialKey(), j->begin.data(), commonLen);
+    if (i < commonLen) {
+      auto c = j->n->partialKey()[i] <=> j->begin[i];
+      if (c > 0) {
+        context->next[job] = down_left_spine;
+        MUSTTAIL return down_left_spine(context, prevJob, job, started, count);
+      } else {
+        j->n = nextSibling(j->n);
+        if (j->n == nullptr) {
+          j->setResult(true);
+          MUSTTAIL return complete(context, prevJob, job, started, count);
+        }
+        context->next[job] = down_left_spine;
+        __builtin_prefetch(j->n);
+        MUSTTAIL return keepGoing(context, prevJob, job, started, count);
+      }
+    }
+    if (commonLen == j->n->partialKeyLen) {
+      // partial key matches
+      j->begin = j->begin.subspan(commonLen, j->begin.size() - commonLen);
+    } else if (j->n->partialKeyLen > int(j->begin.size())) {
+      // n is the first physical node greater than remaining, and there's no
+      // eq node
+      context->next[job] = down_left_spine;
+      MUSTTAIL return down_left_spine(context, prevJob, job, started, count);
+    }
+  }
+
+  if (j->childAndVersion.maxVersion <= j->readVersion) {
+    ++context->tls->point_read_short_circuit_accum;
+    j->setResult(true);
+    MUSTTAIL return complete(context, prevJob, job, started, count);
+  }
+
+  ++context->tls->point_read_iterations_accum;
+
+  if (j->begin.size() == 0) {
+    if (j->n->entryPresent) {
+      j->setResult(j->n->entry.pointVersion <= j->readVersion);
+      MUSTTAIL return complete(context, prevJob, job, started, count);
+    }
+    j->n = getFirstChildExists(j->n);
+    context->next[job] = down_left_spine;
+    __builtin_prefetch(j->n);
+    MUSTTAIL return keepGoing(context, prevJob, job, started, count);
+  }
+
+  j->childAndVersion = getChildAndMaxVersion(j->n, j->begin[0]);
+  __builtin_prefetch(j->childAndVersion.child);
+  // j->next is already iter
+  MUSTTAIL return keepGoing(context, prevJob, job, started, count);
+}
+
+void down_left_spine(struct CheckAll *context, int64_t prevJob, int64_t job,
+                     int64_t started, int64_t count) {
+  auto *j = context->inProgress + job;
+  if (j->n->entryPresent) {
+    j->setResult(j->n->entry.rangeVersion <= j->readVersion);
+    MUSTTAIL return complete(context, prevJob, job, started, count);
+  }
+  j->n = getFirstChildExists(j->n);
+  __builtin_prefetch(j->n);
+  // j->next is already down_left_spine
+  MUSTTAIL return keepGoing(context, prevJob, job, started, count);
+}
+
+} // namespace check_point_read_state_machine
+
+continuation CheckJob::init(const ConflictSet::ReadRange *read,
+                            ConflictSet::Result *result, Node *root,
+                            int64_t oldestVersionFullPrecision,
+                            ReadContext *tls) {
+  auto begin = std::span<const uint8_t>(read->begin.p, read->begin.len);
+  auto end = std::span<const uint8_t>(read->end.p, read->end.len);
+  if (read->readVersion < oldestVersionFullPrecision) {
+    *result = ConflictSet::TooOld;
+    return complete;
+  } else if (end.size() == 0) {
+    this->begin = begin;
+    this->n = root;
+    this->readVersion = InternalVersionT(read->readVersion);
+    this->result = result;
+    return check_point_read_state_machine::begin;
+    // *result =
+    //     checkPointRead(root, begin, InternalVersionT(read->readVersion), tls)
+    //         ? ConflictSet::Commit
+    //         : ConflictSet::Conflict;
+    // return complete;
+  } else {
+    *result = checkRangeRead(root, begin, end,
+                             InternalVersionT(read->readVersion), tls)
+                  ? ConflictSet::Commit
+                  : ConflictSet::Conflict;
+    return complete;
+  }
+}
+
 struct __attribute__((visibility("hidden"))) ConflictSet::Impl {
 
   void check(const ReadRange *reads, Result *result, int count) {
+    assert(oldestVersionFullPrecision >=
+           newestVersionFullPrecision - kNominalVersionWindow);
+
+    if (count == 0) {
+      return;
+    }
+
     ReadContext tls;
     tls.impl = this;
     int64_t check_byte_accum = 0;
+
+    CheckAll context;
+    context.oldestVersionFullPrecision = oldestVersionFullPrecision;
+    context.queries = reads;
+    context.results = result;
+    context.root = root;
+    context.tls = &tls;
+
+    int64_t started = std::min(context.kConcurrent, count);
+    for (int i = 0; i < started; i++) {
+      context.next[i] = context.inProgress[i].init(
+          reads + i, result + i, root, oldestVersionFullPrecision, &tls);
+      context.nextJob[i] = i + 1;
+    }
+    context.nextJob[started - 1] = 0;
+    int prevJob = started - 1;
+    int job = 0;
+    context.next[job](&context, prevJob, job, started, count);
+
     for (int i = 0; i < count; ++i) {
       assert(reads[i].readVersion >= 0);
       assert(reads[i].readVersion <= newestVersionFullPrecision);
       const auto &r = reads[i];
       check_byte_accum += r.begin.len + r.end.len;
-      auto begin = std::span<const uint8_t>(r.begin.p, r.begin.len);
-      auto end = std::span<const uint8_t>(r.end.p, r.end.len);
-      assert(oldestVersionFullPrecision >=
-             newestVersionFullPrecision - kNominalVersionWindow);
-      result[i] =
-          reads[i].readVersion < oldestVersionFullPrecision ? TooOld
-          : (end.size() > 0
-                 ? checkRangeRead(root, begin, end,
-                                  InternalVersionT(reads[i].readVersion), &tls)
-                 : checkPointRead(root, begin,
-                                  InternalVersionT(reads[i].readVersion), &tls))
-              ? Commit
-              : Conflict;
       tls.commits_accum += result[i] == Commit;
       tls.conflicts_accum += result[i] == Conflict;
       tls.too_olds_accum += result[i] == TooOld;
     }
+
     point_read_total.add(tls.point_read_accum);
     prefix_read_total.add(tls.prefix_read_accum);
     range_read_total.add(tls.range_read_accum);
@@ -3242,7 +3400,6 @@ struct __attribute__((visibility("hidden"))) ConflictSet::Impl {
                           0) *
         2;
 
-    memory_bytes.set(totalBytes);
     point_writes_total.add(tls.accum.point_writes);
     range_writes_total.add(tls.accum.range_writes);
     nodes_allocated_total.add(tls.accum.nodes_allocated);
@@ -3331,7 +3488,6 @@ struct __attribute__((visibility("hidden"))) ConflictSet::Impl {
 #endif
     keyUpdates = gcScanStep(keyUpdates);
 
-    memory_bytes.set(totalBytes);
     nodes_allocated_total.add(std::exchange(tls.accum.nodes_allocated, 0));
     nodes_released_total.add(std::exchange(tls.accum.nodes_released, 0));
     entries_inserted_total.add(std::exchange(tls.accum.entries_inserted, 0));
@@ -3379,7 +3535,7 @@ struct __attribute__((visibility("hidden"))) ConflictSet::Impl {
   explicit Impl(int64_t oldestVersion) {
     assert(oldestVersion >= 0);
     init(oldestVersion);
-    initMetrics();
+    metrics = initMetrics(metricsList, metricsCount);
   }
   ~Impl() {
     eraseTree(root, &tls);
@@ -3402,23 +3558,12 @@ struct __attribute__((visibility("hidden"))) ConflictSet::Impl {
 
   MetricsV1 *metrics;
   int metricsCount = 0;
-  void initMetrics() {
+  Metric *metricsList = nullptr;
-    metrics = (MetricsV1 *)safe_malloc(metricsCount * sizeof(metrics[0]));
-    for (auto [i, m] = std::make_tuple(metricsCount - 1, metricList); i >= 0;
-         --i, m = m->prev) {
-      metrics[i].name = m->name;
-      metrics[i].help = m->help;
-      metrics[i].p = m;
-      metrics[i].type = m->type;
-    }
-  }
-
-  Metric *metricList = nullptr;
 
 #define GAUGE(name, help)                                                      \
-  Gauge name { this, #name, help }
+  Gauge name { metricsList, metricsCount, #name, help }
 #define COUNTER(name, help)                                                    \
-  Counter name { this, #name, help }
+  Counter name { metricsList, metricsCount, #name, help }
   // ==================== METRICS DEFINITIONS ====================
   COUNTER(point_read_total, "Total number of point reads checked");
   COUNTER(point_read_short_circuit_total,
@@ -3484,13 +3629,6 @@ struct __attribute__((visibility("hidden"))) ConflictSet::Impl {
   }
 };
 
-Metric::Metric(ConflictSet::Impl *impl, const char *name, const char *help,
-               ConflictSet::MetricsV1::Type type)
-    : prev(std::exchange(impl->metricList, this)), name(name), help(help),
-      type(type), value(0) {
-  ++impl->metricsCount;
-}
-
 Node *&getInTree(Node *n, ConflictSet::Impl *impl) {
   return n->parent == nullptr ? impl->root
                               : getChildExists(n->parent, n->parentsIndex);
@@ -3509,6 +3647,7 @@ void internal_addWrites(ConflictSet::Impl *impl,
   mallocBytesDelta = 0;
   impl->addWrites(writes, count, writeVersion);
   impl->totalBytes += mallocBytesDelta;
+  impl->memory_bytes.set(impl->totalBytes);
 #if SHOW_MEMORY
   if (impl->totalBytes != mallocBytes) {
     abort();
@@ -3520,6 +3659,7 @@ void internal_setOldestVersion(ConflictSet::Impl *impl, int64_t oldestVersion) {
   mallocBytesDelta = 0;
   impl->setOldestVersion(oldestVersion);
   impl->totalBytes += mallocBytesDelta;
+  impl->memory_bytes.set(impl->totalBytes);
 #if SHOW_MEMORY
   if (impl->totalBytes != mallocBytes) {
     abort();
@@ -4073,6 +4213,72 @@ struct __attribute__((visibility("default"))) PeakPrinter {
 
 #ifdef ENABLE_MAIN
 
+#include "third_party/nanobench.h"
+
+template <int kN> void benchRezero() {
+  static_assert(kN % 16 == 0);
+  ankerl::nanobench::Bench bench;
+  InternalVersionT vs[kN];
+  InternalVersionT zero;
+  bench.run("rezero" + std::to_string(kN), [&]() {
+    bench.doNotOptimizeAway(vs);
+    bench.doNotOptimizeAway(zero);
+    for (int i = 0; i < kN; i += 16) {
+      rezero16(vs + i, zero);
+    }
+  });
+}
+
+template <int kN> void benchScan1() {
+  static_assert(kN % 16 == 0);
+  ankerl::nanobench::Bench bench;
+  InternalVersionT vs[kN];
+  uint8_t is[kN];
+  uint8_t begin;
+  uint8_t end;
+  InternalVersionT v;
+  bench.run("scan" + std::to_string(kN), [&]() {
+    bench.doNotOptimizeAway(vs);
+    bench.doNotOptimizeAway(is);
+    bench.doNotOptimizeAway(begin);
+    bench.doNotOptimizeAway(end);
+    bench.doNotOptimizeAway(v);
+    for (int i = 0; i < kN; i += 16) {
+      scan16</*kAVX512=*/true>(vs + i, is + i, begin, end, v);
+    }
+  });
+}
+
+template <int kN> void benchScan2() {
+  static_assert(kN % 16 == 0);
+  ankerl::nanobench::Bench bench;
+  InternalVersionT vs[kN];
+  uint8_t is[kN];
+  uint8_t begin;
+  uint8_t end;
+  InternalVersionT v;
+  bench.run("scan" + std::to_string(kN), [&]() {
+    bench.doNotOptimizeAway(vs);
+    bench.doNotOptimizeAway(begin);
+    bench.doNotOptimizeAway(end);
+    bench.doNotOptimizeAway(v);
+    for (int i = 0; i < kN; i += 16) {
+      scan16</*kAVX512=*/true>(vs + i, begin, end, v);
+    }
+  });
+}
+
+void benchLCP(int len) {
+  ankerl::nanobench::Bench bench;
+  std::vector<uint8_t> lhs(len);
+  std::vector<uint8_t> rhs(len);
+  bench.run("lcp " + std::to_string(len), [&]() {
+    bench.doNotOptimizeAway(lhs);
+    bench.doNotOptimizeAway(rhs);
+    bench.doNotOptimizeAway(longestCommonPrefix(lhs.data(), rhs.data(), len));
+  });
+}
+
 void printTree() {
   int64_t writeVersion = 0;
   ConflictSet::Impl cs{writeVersion};
@@ -4094,7 +4300,11 @@ void printTree() {
   debugPrintDot(stdout, cs.root, &cs);
 }
 
-int main(void) { printTree(); }
+int main(void) {
+  for (int i = 0; i < 256; ++i) {
+    benchLCP(i);
+  }
+}
 #endif
 
 #ifdef ENABLE_FUZZ

InterleavingTest.cpp

@@ -0,0 +1,256 @@
+#include <alloca.h>
+#include <cassert>
+#ifdef __x86_64__
+#include <immintrin.h>
+#endif
+
+#include "third_party/nanobench.h"
+
+struct Job {
+  int *input;
+  // Returned void* is a function pointer to the next continuation. We have to
+  // use void* because otherwise the type would be recursive.
+  typedef void *(*continuation)(Job *);
+  continuation next;
+};
+
+void *stepJob(Job *j) {
+  auto done = --(*j->input) == 0;
+#ifdef __x86_64__
+  _mm_clflush(j->input);
+#endif
+  return done ? nullptr : (void *)stepJob;
+}
+
+void sequential(Job **jobs, int count) {
+  for (int i = 0; i < count; ++i) {
+    do {
+      jobs[i]->next = (Job::continuation)jobs[i]->next(jobs[i]);
+    } while (jobs[i]->next);
+  }
+}
+
+void sequentialNoFuncPtr(Job **jobs, int count) {
+  for (int i = 0; i < count; ++i) {
+    while (stepJob(jobs[i]))
+      ;
+  }
+}
+
+void interleaveSwapping(Job **jobs, int remaining) {
+  int current = 0;
+  while (remaining > 0) {
+    auto next = (Job::continuation)jobs[current]->next(jobs[current]);
+    jobs[current]->next = next;
+    if (next == nullptr) {
+      jobs[current] = jobs[remaining - 1];
+      --remaining;
+    } else {
+      ++current;
+    }
+    if (current == remaining) {
+      current = 0;
+    }
+  }
+}
+
+void interleaveBoundedCyclicList(Job **jobs, int count) {
+  if (count == 0) {
+    return;
+  }
+
+  constexpr int kConcurrent = 32;
+  Job *inProgress[kConcurrent];
+  int nextJob[kConcurrent];
+
+  int started = std::min(kConcurrent, count);
+  for (int i = 0; i < started; i++) {
+    inProgress[i] = jobs[i];
+    nextJob[i] = i + 1;
+  }
+  nextJob[started - 1] = 0;
+
+  int prevJob = started - 1;
+  int job = 0;
+  for (;;) {
+    auto next = (Job::continuation)inProgress[job]->next(inProgress[job]);
+    inProgress[job]->next = next;
+    if (next == nullptr) {
+      if (started == count) {
+        if (prevJob == job)
+          break;
+        nextJob[prevJob] = nextJob[job];
+        job = prevJob;
+      } else {
+        int temp = started++;
+        inProgress[job] = jobs[temp];
+      }
+    }
+    prevJob = job;
+    job = nextJob[job];
+  }
+}
+
+#ifndef __has_attribute
+#define __has_attribute(x) 0
+#endif
+
+#if __has_attribute(musttail)
+#define MUSTTAIL __attribute__((musttail))
+#else
+#define MUSTTAIL
+#endif
+
+struct Context {
+  constexpr static int kConcurrent = 32;
+  Job **jobs;
+  Job *inProgress[kConcurrent];
+  void (*continuation[kConcurrent])(Context *, int64_t prevJob, int64_t job,
+                                    int64_t started, int64_t count);
+  int nextJob[kConcurrent];
+};
+
+void keepGoing(Context *context, int64_t prevJob, int64_t job, int64_t started,
+               int64_t count) {
+  prevJob = job;
+  job = context->nextJob[job];
+  MUSTTAIL return context->continuation[job](context, prevJob, job, started,
+                                             count);
+}
+
+void stepJobTailCall(Context *context, int64_t prevJob, int64_t job,
+                     int64_t started, int64_t count);
+
+void complete(Context *context, int64_t prevJob, int64_t job, int64_t started,
+              int64_t count) {
+  if (started == count) {
+    if (prevJob == job) {
+      return;
+    }
+    context->nextJob[prevJob] = context->nextJob[job];
+    job = prevJob;
+  } else {
+    context->inProgress[job] = context->jobs[started++];
+    context->continuation[job] = stepJobTailCall;
+  }
+  prevJob = job;
+  job = context->nextJob[job];
+  MUSTTAIL return context->continuation[job](context, prevJob, job, started,
+                                             count);
+}
+
+void stepJobTailCall(Context *context, int64_t prevJob, int64_t job,
+                     int64_t started, int64_t count) {
+  auto *j = context->inProgress[job];
+  auto done = --(*j->input) == 0;
+#ifdef __x86_64__
+  _mm_clflush(j->input);
+#endif
+  if (done) {
+    MUSTTAIL return complete(context, prevJob, job, started, count);
+  } else {
+    context->continuation[job] = stepJobTailCall;
+    MUSTTAIL return keepGoing(context, prevJob, job, started, count);
+  }
+}
+
+void useTailCalls(Job **jobs, int count) {
+  if (count == 0) {
+    return;
+  }
+  Context context;
+  context.jobs = jobs;
+  int64_t started = std::min(Context::kConcurrent, count);
+  for (int i = 0; i < started; i++) {
+    context.inProgress[i] = jobs[i];
+    context.nextJob[i] = i + 1;
+    context.continuation[i] = stepJobTailCall;
+  }
+  context.nextJob[started - 1] = 0;
+  int prevJob = started - 1;
+  int job = 0;
+  return context.continuation[job](&context, prevJob, job, started, count);
+}
+
+void interleaveCyclicList(Job **jobs, int count) {
+  auto *nextJob = (int *)alloca(sizeof(int) * count);
+
+  for (int i = 0; i < count - 1; ++i) {
+    nextJob[i] = i + 1;
+  }
+  nextJob[count - 1] = 0;
+
+  int prevJob = count - 1;
+  int job = 0;
+  for (;;) {
+    auto next = (Job::continuation)jobs[job]->next(jobs[job]);
+    jobs[job]->next = next;
+    if (next == nullptr) {
+      if (prevJob == job)
+        break;
+      nextJob[prevJob] = nextJob[job];
+      job = prevJob;
+    }
+    prevJob = job;
+    job = nextJob[job];
+  }
+}
+
+int main() {
+  ankerl::nanobench::Bench bench;
+
+  constexpr int kNumJobs = 10000;
+  bench.relative(true);
+
+  Job jobs[kNumJobs];
+  Job jobsCopy[kNumJobs];
+  int iters = 0;
+  int originalInput[kNumJobs];
+  for (int i = 0; i < kNumJobs; ++i) {
+    originalInput[i] = rand() % 5 + 3;
+    jobs[i].input = new int{originalInput[i]};
+    jobs[i].next = stepJob;
+    iters += *jobs[i].input;
+  }
+  bench.batch(iters);
+
+  for (auto [scheduler, name] :
+       {std::make_pair(sequentialNoFuncPtr, "sequentialNoFuncPtr"),
+        std::make_pair(sequential, "sequential"),
+        std::make_pair(useTailCalls, "useTailCalls"),
+        std::make_pair(interleaveSwapping, "interleavingSwapping"),
+        std::make_pair(interleaveBoundedCyclicList,
+                       "interleaveBoundedCyclicList"),
+        std::make_pair(interleaveCyclicList, "interleaveCyclicList")}) {
+    for (int i = 0; i < kNumJobs; ++i) {
+      *jobs[i].input = originalInput[i];
+    }
+    memcpy(jobsCopy, jobs, sizeof(jobs));
+    Job *ps[kNumJobs];
+    for (int i = 0; i < kNumJobs; ++i) {
+      ps[i] = jobsCopy + i;
+    }
+    scheduler(ps, kNumJobs);
+    for (int i = 0; i < kNumJobs; ++i) {
+      if (*jobsCopy[i].input != 0) {
+        fprintf(stderr, "%s failed\n", name);
+        abort();
+      }
+    }
+
+    bench.run(name, [&]() {
+      for (int i = 0; i < kNumJobs; ++i) {
+        *jobs[i].input = originalInput[i];
+      }
+      memcpy(jobsCopy, jobs, sizeof(jobs));
+      Job *ps[kNumJobs];
+      for (int i = 0; i < kNumJobs; ++i) {
+        ps[i] = jobsCopy + i;
+      }
+      scheduler(ps, kNumJobs);
+    });
+  }
+  for (int i = 0; i < kNumJobs; ++i) {
+    delete jobs[i].input;
+  }
+}

Jenkinsfile

@@ -129,7 +129,7 @@ pipeline {
             }
             steps {
                 script {
-                    filter_args = "-f ConflictSet.cpp -f LongestCommonPrefix.h"
+                    filter_args = "-f ConflictSet.cpp -f LongestCommonPrefix.h -f Metrics.h"
                 }
                 CleanBuildAndTest("-DCMAKE_C_COMPILER=gcc -DCMAKE_CXX_COMPILER=g++ -DCMAKE_C_FLAGS=--coverage -DCMAKE_CXX_FLAGS=--coverage -DCMAKE_BUILD_TYPE=Debug -DDISABLE_TSAN=ON")
                 sh """

Metrics.h

@@ -0,0 +1,64 @@
+#pragma once
+
+#include "ConflictSet.h"
+#include "Internal.h"
+
+#include <assert.h>
+#include <atomic>
+#include <tuple>
+
+struct Metric {
+  Metric *prev;
+  const char *name;
+  const char *help;
+  weaselab::ConflictSet::MetricsV1::Type type;
+  std::atomic<int64_t> value;
+
+protected:
+  Metric(Metric *&metricList, int &metricsCount, const char *name,
+         const char *help, weaselab::ConflictSet::MetricsV1::Type type)
+      : prev(std::exchange(metricList, this)), name(name), help(help),
+        type(type), value(0) {
+    ++metricsCount;
+  }
+};
+
+struct Gauge : private Metric {
+  Gauge(Metric *&metricList, int &metricsCount, const char *name,
+        const char *help)
+      : Metric(metricList, metricsCount, name, help,
+               weaselab::ConflictSet::MetricsV1::Gauge) {}
+
+  void set(int64_t value) {
+    this->value.store(value, std::memory_order_relaxed);
+  }
+};
+
+struct Counter : private Metric {
+  Counter(Metric *&metricList, int &metricsCount, const char *name,
+          const char *help)
+      : Metric(metricList, metricsCount, name, help,
+               weaselab::ConflictSet::MetricsV1::Counter) {}
+  // Expensive. Accumulate locally and then call add instead of repeatedly
+  // calling add.
+  void add(int64_t value) {
+    assert(value >= 0);
+    static_assert(std::atomic<int64_t>::is_always_lock_free);
+    this->value.fetch_add(value, std::memory_order_relaxed);
+  }
+};
+
+inline weaselab::ConflictSet::MetricsV1 *initMetrics(Metric *metricsList,
+                                                     int metricsCount) {
+  weaselab::ConflictSet::MetricsV1 *metrics =
+      (weaselab::ConflictSet::MetricsV1 *)safe_malloc(metricsCount *
+                                                      sizeof(metrics[0]));
+  for (auto [i, m] = std::make_tuple(metricsCount - 1, metricsList); i >= 0;
+       --i, m = m->prev) {
+    metrics[i].name = m->name;
+    metrics[i].help = m->help;
+    metrics[i].p = m;
+    metrics[i].type = m->type;
+  }
+  return metrics;
+}

README.md

@@ -24,15 +24,15 @@ Hardware for all benchmarks is an AMD Ryzen 9 7900 with (2x32GB) 5600MT/s CL28-3
 
 |               ns/op |                op/s |    err% |          ins/op |          cyc/op |    IPC |         bra/op |   miss% |     total | benchmark
 |--------------------:|--------------------:|--------:|----------------:|----------------:|-------:|---------------:|--------:|----------:|:----------
-|               11.18 |       89,455,125.34 |    0.6% |          185.37 |           57.08 |  3.248 |          41.51 |    0.4% |      0.01 | `point reads`
+|               12.88 |       77,653,350.77 |    0.5% |          185.37 |           64.45 |  2.876 |          41.51 |    0.4% |      0.01 | `point reads`
-|               14.53 |       68,800,688.89 |    0.4% |          282.41 |           74.80 |  3.776 |          55.06 |    0.3% |      0.01 | `prefix reads`
+|               14.67 |       68,179,354.49 |    0.1% |          271.44 |           73.40 |  3.698 |          53.70 |    0.3% |      0.01 | `prefix reads`
-|               36.54 |       27,367,576.87 |    0.2% |          798.06 |          188.90 |  4.225 |         141.69 |    0.2% |      0.01 | `range reads`
+|               34.84 |       28,701,444.36 |    0.3% |          715.74 |          175.27 |  4.084 |         127.30 |    0.2% |      0.01 | `range reads`
-|               16.69 |       59,912,106.02 |    0.6% |          314.57 |           86.29 |  3.645 |          39.84 |    0.4% |      0.01 | `point writes`
+|               17.12 |       58,422,988.28 |    0.2% |          314.30 |           86.11 |  3.650 |          39.82 |    0.4% |      0.01 | `point writes`
-|               30.09 |       33,235,744.07 |    0.5% |          591.33 |          155.92 |  3.793 |          82.69 |    0.2% |      0.01 | `prefix writes`
+|               31.42 |       31,830,804.65 |    0.1% |          591.06 |          158.07 |  3.739 |          82.67 |    0.2% |      0.01 | `prefix writes`
-|               35.77 |       27,956,388.03 |    1.4% |          682.25 |          187.63 |  3.636 |          96.12 |    0.1% |      0.01 | `range writes`
+|               37.37 |       26,759,432.70 |    2.2% |          681.98 |          188.95 |  3.609 |          96.10 |    0.1% |      0.01 | `range writes`
-|               74.04 |       13,505,408.41 |    2.7% |        1,448.95 |          392.10 |  3.695 |         260.53 |    0.1% |      0.01 | `monotonic increasing point writes`
+|               76.72 |       13,035,140.63 |    2.3% |        1,421.28 |          387.17 |  3.671 |         257.76 |    0.1% |      0.01 | `monotonic increasing point writes`
-|          330,984.50 |            3,021.29 |    1.9% |    3,994,153.50 |    1,667,309.00 |  2.396 |     806,019.50 |    0.0% |      0.01 | `worst case for radix tree`
+|          297,452.00 |            3,361.89 |    0.9% |    3,508,083.00 |    1,500,834.67 |  2.337 |     727,525.33 |    0.1% |      0.01 | `worst case for radix tree`
-|               92.46 |       10,814,961.65 |    0.5% |        1,800.00 |          463.41 |  3.884 |         297.00 |    0.0% |      0.01 | `create and destroy`
+|               87.70 |       11,402,490.60 |    1.0% |        1,795.00 |          442.09 |  4.060 |         297.00 |    0.0% |      0.01 | `create and destroy`
 
 # "Real data" test
 

ServerBench.cpp

@@ -1,4 +1,5 @@
 #include <atomic>
+#include <cstdint>
 #include <errno.h>
 #include <netdb.h>
 #include <stdio.h>
@@ -21,78 +22,55 @@
 
 std::atomic<int64_t> transactions;
 
-constexpr int kBaseSearchDepth = 32;
 constexpr int kWindowSize = 10000000;
 
-std::string numToKey(int64_t num) {
+constexpr int kNumPrefixes = 250000;
+
+std::string makeKey(int64_t num, int suffixLen) {
   std::string result;
-  result.resize(kBaseSearchDepth + sizeof(int64_t));
+  result.resize(sizeof(int64_t) + suffixLen);
-  memset(result.data(), 0, kBaseSearchDepth);
   int64_t be = __builtin_bswap64(num);
-  memcpy(result.data() + kBaseSearchDepth, &be, sizeof(int64_t));
+  memcpy(result.data(), &be, sizeof(int64_t));
+  memset(result.data() + sizeof(int64_t), 0, suffixLen);
   return result;
 }
 
 void workload(weaselab::ConflictSet *cs) {
   int64_t version = kWindowSize;
-  cs->addWrites(nullptr, 0, version);
+  for (int i = 0; i < kNumPrefixes; ++i) {
+    for (int j = 0; j < 50; ++j) {
+      weaselab::ConflictSet::WriteRange wr;
+      auto k = makeKey(i, j);
+      wr.begin.p = (const uint8_t *)k.data();
+      wr.begin.len = k.size();
+      wr.end.len = 0;
+      cs->addWrites(&wr, 1, version);
+    }
+  }
+  ++version;
+  for (int i = 0; i < kNumPrefixes; ++i) {
+    weaselab::ConflictSet::WriteRange wr;
+    auto k = makeKey(i, 50);
+    wr.begin.p = (const uint8_t *)k.data();
+    wr.begin.len = k.size();
+    wr.end.len = 0;
+    cs->addWrites(&wr, 1, version);
+  }
+
+  std::vector<weaselab::ConflictSet::Result> results(10);
   for (;; transactions.fetch_add(1, std::memory_order_relaxed)) {
-    // Reads
+    std::vector<std::string> keys(10);
-    {
+    for (auto &k : keys) {
-      auto beginK = numToKey(version - kWindowSize);
+      k = makeKey(rand() % kNumPrefixes, 49);
-      auto endK = numToKey(version - 1);
-      auto pointRv = version - kWindowSize + rand() % kWindowSize + 1;
-      auto pointK = numToKey(pointRv);
-      weaselab::ConflictSet::ReadRange reads[] = {
-          {
-              {(const uint8_t *)pointK.data(), int(pointK.size())},
-              {nullptr, 0},
-              pointRv,
-          },
-          {
-              {(const uint8_t *)beginK.data(), int(beginK.size())},
-              {(const uint8_t *)endK.data(), int(endK.size())},
-              version - 2,
-          },
-      };
-      weaselab::ConflictSet::Result result[sizeof(reads) / sizeof(reads[0])];
-      cs->check(reads, result, sizeof(reads) / sizeof(reads[0]));
-      // for (int i = 0; i < sizeof(reads) / sizeof(reads[0]); ++i) {
-      //   if (result[i] != weaselab::ConflictSet::Commit) {
-      //     fprintf(stderr, "Unexpected conflict: [%s, %s) @ %" PRId64 "\n",
-      //             printable(reads[i].begin).c_str(),
-      //             printable(reads[i].end).c_str(), reads[i].readVersion);
-      //     abort();
-      //   }
-      // }
     }
-    // Writes
+    std::vector<weaselab::ConflictSet::ReadRange> reads(10);
-    {
+    for (int i = 0; i < reads.size(); ++i) {
-      weaselab::ConflictSet::WriteRange w;
+      reads[i].begin.p = (const uint8_t *)(keys[i].data());
-      auto k = numToKey(version);
+      reads[i].begin.len = keys[i].size();
-      w.begin.p = (const uint8_t *)k.data();
+      reads[i].end.len = 0;
-      w.end.len = 0;
+      reads[i].readVersion = version - 1;
-      if (version % (kWindowSize / 2) == 0) {
-        for (int l = 0; l <= k.size(); ++l) {
-          w.begin.len = l;
-          cs->addWrites(&w, 1, version);
-        }
-      } else {
-        w.begin.len = k.size();
-        cs->addWrites(&w, 1, version);
-        int64_t beginN = version - kWindowSize + rand() % kWindowSize;
-        auto b = numToKey(beginN);
-        auto e = numToKey(beginN + 1000);
-        w.begin.p = (const uint8_t *)b.data();
-        w.begin.len = b.size();
-        w.end.p = (const uint8_t *)e.data();
-        w.end.len = e.size();
-        cs->addWrites(&w, 1, version);
-      }
     }
-    // GC
+    cs->check(reads.data(), results.data(), 10);
-    cs->setOldestVersion(version - kWindowSize);
-    ++version;
   }
 }
 

SkipList.cpp

@@ -22,6 +22,7 @@
 
 #include "ConflictSet.h"
 #include "Internal.h"
+#include "Metrics.h"
 
 #include <algorithm>
 #include <span>
@@ -434,13 +435,14 @@ public:
     return result;
   }
 
-  void detectConflicts(ReadConflictRange *ranges, int count,
+  // Return number of iterations of main loop
-                       ConflictSet::Result *transactionConflictStatus) const {
+  int detectConflicts(ReadConflictRange *ranges, int count,
+                      ConflictSet::Result *transactionConflictStatus) const {
     const int M = 16;
     int nextJob[M];
     CheckMax inProgress[M];
     if (!count)
-      return;
+      return 0;
 
     int started = std::min(M, count);
     for (int i = 0; i < started; i++) {
@@ -451,8 +453,9 @@ public:
 
     int prevJob = started - 1;
     int job = 0;
+    int iters = 0;
     // vtune: 340 parts
-    while (true) {
+    for (;; ++iters) {
       if (inProgress[job].advance()) {
         if (started == count) {
           if (prevJob == job)
@@ -468,6 +471,7 @@ public:
       prevJob = job;
       job = nextJob[job];
     }
+    return iters;
   }
 
   void find(const StringRef *values, Finger *results, int *temp, int count) {
@@ -702,15 +706,27 @@ private:
   };
 };
 
+struct ReadContext {
+  int64_t commits_accum = 0;
+  int64_t conflicts_accum = 0;
+  int64_t too_olds_accum = 0;
+  int64_t check_bytes_accum = 0;
+};
+
 struct __attribute__((visibility("hidden"))) ConflictSet::Impl {
   Impl(int64_t oldestVersion)
       : oldestVersion(oldestVersion), newestVersion(oldestVersion),
-        skipList(oldestVersion) {}
+        skipList(oldestVersion) {
+    metrics = initMetrics(metricsList, metricsCount);
+  }
+  ~Impl() { safe_free(metrics, metricsCount * sizeof(metrics[0])); }
   void check(const ConflictSet::ReadRange *reads, ConflictSet::Result *results,
-             int count) const {
+             int count) {
+    ReadContext tls;
     Arena arena;
     auto *ranges = new (arena) ReadConflictRange[count];
     for (int i = 0; i < count; ++i) {
+      tls.check_bytes_accum += reads[i].begin.len + reads[i].end.len;
       ranges[i].begin = {reads[i].begin.p, size_t(reads[i].begin.len)};
       ranges[i].end = reads[i].end.len > 0
                           ? StringRef{reads[i].end.p, size_t(reads[i].end.len)}
@@ -718,13 +734,22 @@ struct __attribute__((visibility("hidden"))) ConflictSet::Impl {
       ranges[i].version = reads[i].readVersion;
       results[i] = ConflictSet::Commit;
     }
-    skipList.detectConflicts(ranges, count, results);
+    int iters = skipList.detectConflicts(ranges, count, results);
     for (int i = 0; i < count; ++i) {
       if (reads[i].readVersion < oldestVersion ||
           reads[i].readVersion < newestVersion - 2e9) {
         results[i] = TooOld;
       }
+      tls.commits_accum += results[i] == Commit;
+      tls.conflicts_accum += results[i] == Conflict;
+      tls.too_olds_accum += results[i] == TooOld;
     }
+    range_read_iterations_total.add(iters);
+    range_read_total.add(count);
+    commits_total.add(tls.commits_accum);
+    conflicts_total.add(tls.conflicts_accum);
+    too_olds_total.add(tls.too_olds_accum);
+    check_bytes_total.add(tls.check_bytes_accum);
   }
 
   void addWrites(const ConflictSet::WriteRange *writes, int count,
@@ -788,6 +813,9 @@ struct __attribute__((visibility("hidden"))) ConflictSet::Impl {
   }
 
   void setOldestVersion(int64_t oldestVersion) {
+    // This isn't 100% accurate. It overcounts if you hit the end
+    gc_iterations_total.add(keyUpdates);
+
     assert(oldestVersion >= this->oldestVersion);
     this->oldestVersion = oldestVersion;
     SkipList::Finger finger;
@@ -802,6 +830,54 @@ struct __attribute__((visibility("hidden"))) ConflictSet::Impl {
 
   int64_t totalBytes = 0;
 
+  MetricsV1 *metrics;
+  int metricsCount = 0;
+  Metric *metricsList = nullptr;
+
+#define GAUGE(name, help)                                                      \
+  Gauge name { metricsList, metricsCount, #name, help }
+#define COUNTER(name, help)                                                    \
+  Counter name { metricsList, metricsCount, #name, help }
+  // ==================== METRICS DEFINITIONS ====================
+  COUNTER(range_read_total, "Total number of range reads checked");
+  COUNTER(range_read_iterations_total,
+          "Total number of iterations of the main loops for range read checks");
+  COUNTER(commits_total,
+          "Total number of checks where the result is \"commit\"");
+  COUNTER(conflicts_total,
+          "Total number of checks where the result is \"conflict\"");
+  COUNTER(too_olds_total,
+          "Total number of checks where the result is \"too old\"");
+  COUNTER(check_bytes_total, "Total number of key bytes checked");
+  GAUGE(memory_bytes, "Total number of bytes in use");
+  COUNTER(nodes_allocated_total,
+          "The total number of physical tree nodes allocated");
+  COUNTER(nodes_released_total,
+          "The total number of physical tree nodes released");
+  COUNTER(insert_iterations_total,
+          "The total number of iterations of the main loop for insertion. "
+          "Includes searches where the entry already existed, and so insertion "
+          "did not take place");
+  COUNTER(entries_inserted_total,
+          "The total number of entries inserted in the tree");
+  COUNTER(entries_erased_total,
+          "The total number of entries erased from the tree");
+  COUNTER(
+      gc_iterations_total,
+      "The total number of iterations of the main loop for garbage collection");
+  COUNTER(write_bytes_total, "Total number of key bytes in calls to addWrites");
+  GAUGE(oldest_version,
+        "The lowest version that doesn't result in \"TooOld\" for checks");
+  GAUGE(newest_version, "The version of the most recent call to addWrites");
+  // ==================== END METRICS DEFINITIONS ====================
+#undef GAUGE
+#undef COUNTER
+
+  void getMetricsV1(MetricsV1 **metrics, int *count) {
+    *metrics = this->metrics;
+    *count = metricsCount;
+  }
+
 private:
   int64_t keyUpdates = 0;
   Arena removalArena;
@@ -824,6 +900,7 @@ void internal_addWrites(ConflictSet::Impl *impl,
   mallocBytesDelta = 0;
   impl->addWrites(writes, count, writeVersion);
   impl->totalBytes += mallocBytesDelta;
+  impl->memory_bytes.set(impl->totalBytes);
 #if SHOW_MEMORY
   if (impl->totalBytes != mallocBytes) {
     abort();
@@ -835,6 +912,7 @@ void internal_setOldestVersion(ConflictSet::Impl *impl, int64_t oldestVersion) {
   mallocBytesDelta = 0;
   impl->setOldestVersion(oldestVersion);
   impl->totalBytes += mallocBytesDelta;
+  impl->memory_bytes.set(impl->totalBytes);
 #if SHOW_MEMORY
   if (impl->totalBytes != mallocBytes) {
     abort();
@@ -858,12 +936,11 @@ int64_t internal_getBytes(ConflictSet::Impl *impl) { return impl->totalBytes; }
 
 void internal_getMetricsV1(ConflictSet::Impl *impl,
                            ConflictSet::MetricsV1 **metrics, int *count) {
-  *metrics = nullptr;
+  return impl->getMetricsV1(metrics, count);
-  *count = 0;
 }
 
 double internal_getMetricValue(const ConflictSet::MetricsV1 *metric) {
-  return 0;
+  return ((Metric *)metric->p)->value.load(std::memory_order_relaxed);
 }
 
 void ConflictSet::check(const ReadRange *reads, Result *results,