Fix bugs found by exercising the code

.clangd

@@ -1,2 +1,2 @@
 CompileFlags:
-  Add: [-DENABLE_MAIN, -UNDEBUG, -DENABLE_FUZZ, -DTHREAD_TEST, -fexceptions]
+  Add: [-DENABLE_MAIN, -UNDEBUG, -DENABLE_FUZZ, -DTHREAD_TEST, -fexceptions, -DDEBUG_VERBOSE=1]

VersionedMap.cpp

@@ -9,6 +9,10 @@
 #include <unordered_set>
 #include <xxhash.h>
 
+#ifndef DEBUG_VERBOSE
+#define DEBUG_VERBOSE 0
+#endif
+
 void *mmapSafe(void *addr, size_t len, int prot, int flags, int fd,
                off_t offset) {
   void *result = mmap(addr, len, prot, flags, fd, offset);
@@ -254,6 +258,9 @@ struct MemManager {
     if (newFirstUnaddressable < firstUnaddressable) {
       for (int i = newFirstUnaddressable; i < firstUnaddressable; ++i) {
         if (base[i].entry != nullptr) {
+#if DEBUG_VERBOSE
+          printf("Collecting %u\n", i);
+#endif
           base[i].entry->delref();
         }
       }
@@ -269,6 +276,9 @@ struct MemManager {
     reachable.iterateAbsentApproxBackwards(
         [&](uint32_t i) {
           if (base[i].entry != nullptr) {
+#if DEBUG_VERBOSE
+            printf("Collecting %u\n", i);
+#endif
             base[i].entry->delref();
             base[i].entry = nullptr;
           }
@@ -311,7 +321,7 @@ struct RootSet {
   /// Inform that there will be no calls to rootForVersion with a version less
   /// than `oldestVersion`
   void setOldestVersion(int64_t oldestVersion) {
-    const uint32_t firstToKeep = rootForVersion(oldestVersion);
+    const uint32_t firstToKeep = lastLeq(oldestVersion);
 
     if (firstToKeep != 0) {
       memmove(nodes, nodes + firstToKeep,
@@ -321,29 +331,12 @@ struct RootSet {
       end -= firstToKeep;
     }
     assert(end > 0);
-    assert(nodes[0] <= oldestVersion);
+    assert(versions[0] <= oldestVersion);
   }
 
   /// Get a root node that can correctly be used for `version`
   uint32_t rootForVersion(int64_t version) const {
-    assert(end > 0);
-    assert(nodes[0] <= version);
-
-    // Find the last version <= oldestVersion
-    int left = 0;
-    int right = end;
-    int result = 0;
-    while (left <= right) {
-      int mid = left + (right - left) / 2;
-      if (versions[mid] <= version) {
-        result = mid;
-        left = mid + 1;
-      } else {
-        right = mid - 1;
-      }
-    }
-    assert(result < end);
-    return result;
+    return nodes[lastLeq(version)];
   }
 
   const uint32_t *roots() const { return nodes; }
@@ -364,6 +357,26 @@ struct RootSet {
   }
 
 private:
+  uint32_t lastLeq(int64_t version) const {
+    assert(end > 0);
+    assert(versions[0] <= version);
+
+    // Find the last version <= oldestVersion
+    int left = 1;
+    int right = end - 1;
+    int result = 0;
+    while (left <= right) {
+      int mid = left + (right - left) / 2;
+      if (versions[mid] <= version) {
+        result = mid;
+        left = mid + 1;
+      } else {
+        right = mid - 1;
+      }
+    }
+    assert(result < end);
+    return result;
+  }
   uint32_t *nodes;
   // versions[i] is the version of nodes[i]
   int64_t *versions;
@@ -463,6 +476,27 @@ struct VersionedMap::Impl {
     return result;
   }
 
+  void setOldestVersion(int64_t oldestVersion) {
+    roots.setOldestVersion(oldestVersion);
+    mm.gc(roots.roots(), roots.rootCount(), oldestVersion);
+  }
+
+  void printInOrder(int64_t version) {
+    printInOrderHelper(version, roots.rootForVersion(version));
+  }
+
+  void printInOrderHelper(int64_t version, uint32_t node) {
+    if (node == 0) {
+      return;
+    }
+    printInOrderHelper(version,
+                       child<std::memory_order_relaxed>(node, false, version));
+    printf("%.*s\n", (int)mm.base[node].entry->keyLen,
+           mm.base[node].entry->getKey());
+    printInOrderHelper(version,
+                       child<std::memory_order_relaxed>(node, true, version));
+  }
+
   MemManager mm;
   RootSet roots;
 };
@@ -472,6 +506,23 @@ struct VersionedMap::Impl {
 #include <nanobench.h>
 
 int main() {
+
+  {
+    weaselab::VersionedMap::Impl impl;
+    impl.roots.add(impl.newNode(1, (const uint8_t *)"a", 1, nullptr, -1, false),
+                   1);
+    impl.roots.add(impl.newNode(2, (const uint8_t *)"b", 1, nullptr, -1, false),
+                   2);
+    impl.roots.add(impl.newNode(3, (const uint8_t *)"c", 1, nullptr, -1, false),
+                   3);
+    impl.printInOrder(0);
+    impl.printInOrder(1);
+    impl.printInOrder(2);
+    impl.printInOrder(3);
+    impl.setOldestVersion(3);
+  }
+  return 0;
+
   ankerl::nanobench::Bench bench;
   bench.minEpochIterations(5000);
   weaselab::MemManager mm;