From cdf42fcb34799468b0cc2dcda33fc1657ba9edc3 Mon Sep 17 00:00:00 2001
From: Andrew Noyes <andrew@weaselab.dev>
Date: Tue, 2 Jul 2024 13:06:53 -0700
Subject: [PATCH] Add gcScanStep

Also remove oldestVersion arg in write call tree
---
 ConflictSet.cpp | 66 ++++++++++++++++++++++++++-----------------------
 1 file changed, 35 insertions(+), 31 deletions(-)

diff --git a/ConflictSet.cpp b/ConflictSet.cpp
index b29735c..5ff7f65 100644
--- a/ConflictSet.cpp
+++ b/ConflictSet.cpp
@@ -2646,9 +2646,9 @@ void destroyTree(Node *root) {
   }
 }
 
-void addPointWrite(Node *&root, InternalVersionT oldestVersion,
-                   std::span<const uint8_t> key, InternalVersionT writeVersion,
-                   NodeAllocators *allocators, ConflictSet::Impl *impl) {
+void addPointWrite(Node *&root, std::span<const uint8_t> key,
+                   InternalVersionT writeVersion, NodeAllocators *allocators,
+                   ConflictSet::Impl *impl) {
   auto *n = insert<true>(&root, key, writeVersion, allocators, impl);
   if (!n->entryPresent) {
     auto *p = nextLogical(n);
@@ -2659,24 +2659,22 @@ void addPointWrite(Node *&root, InternalVersionT oldestVersion,
     n->entry.pointVersion = writeVersion;
     setMaxVersion(n, impl, writeVersion);
     n->entry.rangeVersion =
-        p != nullptr ? p->entry.rangeVersion : oldestVersion;
+        p != nullptr ? p->entry.rangeVersion : InternalVersionT::zero;
   } else {
     assert(writeVersion >= n->entry.pointVersion);
     n->entry.pointVersion = writeVersion;
   }
 }
 
-void addWriteRange(Node *&root, InternalVersionT oldestVersion,
-                   std::span<const uint8_t> begin, std::span<const uint8_t> end,
-                   InternalVersionT writeVersion, NodeAllocators *allocators,
-                   ConflictSet::Impl *impl) {
+void addWriteRange(Node *&root, std::span<const uint8_t> begin,
+                   std::span<const uint8_t> end, InternalVersionT writeVersion,
+                   NodeAllocators *allocators, ConflictSet::Impl *impl) {
 
   int lcp = longestCommonPrefix(begin.data(), end.data(),
                                 std::min(begin.size(), end.size()));
   if (lcp == int(begin.size()) && end.size() == begin.size() + 1 &&
       end.back() == 0) {
-    return addPointWrite(root, oldestVersion, begin, writeVersion, allocators,
-                         impl);
+    return addPointWrite(root, begin, writeVersion, allocators, impl);
   }
   const bool beginIsPrefix = lcp == int(begin.size());
   auto remaining = begin.subspan(0, lcp);
@@ -2724,7 +2722,7 @@ void addWriteRange(Node *&root, InternalVersionT oldestVersion,
   if (insertedBegin) {
     auto *p = nextLogical(beginNode);
     beginNode->entry.rangeVersion =
-        p != nullptr ? p->entry.rangeVersion : oldestVersion;
+        p != nullptr ? p->entry.rangeVersion : InternalVersionT::zero;
     beginNode->entry.pointVersion = writeVersion;
     assert(maxVersion(beginNode, impl) <= writeVersion);
     setMaxVersion(beginNode, impl, writeVersion);
@@ -2743,7 +2741,7 @@ void addWriteRange(Node *&root, InternalVersionT oldestVersion,
   if (insertedEnd) {
     auto *p = nextLogical(endNode);
     endNode->entry.pointVersion =
-        p != nullptr ? p->entry.rangeVersion : oldestVersion;
+        p != nullptr ? p->entry.rangeVersion : InternalVersionT::zero;
     auto m = maxVersion(endNode, impl);
     setMaxVersion(endNode, impl,
                   std::max<InternalVersionT>(m, endNode->entry.pointVersion));
@@ -2862,30 +2860,18 @@ struct __attribute__((visibility("hidden"))) ConflictSet::Impl {
       auto end = std::span<const uint8_t>(w.end.p, w.end.len);
       if (w.end.len > 0) {
         keyUpdates += 3;
-        addWriteRange(root, oldestVersion, begin, end,
-                      InternalVersionT(writeVersion), &allocators, this);
+        addWriteRange(root, begin, end, InternalVersionT(writeVersion),
+                      &allocators, this);
       } else {
         keyUpdates += 2;
-        addPointWrite(root, oldestVersion, begin,
-                      InternalVersionT(writeVersion), &allocators, this);
+        addPointWrite(root, begin, InternalVersionT(writeVersion), &allocators,
+                      this);
       }
     }
   }
 
-  void setOldestVersion(int64_t o) {
-    InternalVersionT oldestVersion{o};
-    assert(o >= oldestVersionFullPrecision);
-    this->oldestVersionFullPrecision = o;
-    this->oldestVersion = oldestVersion;
-    InternalVersionT::zero = oldestVersion;
-#ifdef NDEBUG
-    // This is here for performance reasons, since we want to amortize the cost
-    // of storing the search path as a string. In tests, we want to exercise the
-    // rest of the code often.
-    if (keyUpdates < 100) {
-      return;
-    }
-#endif
+  // Spends up to `fuel` gc'ing, and returns its unused fuel
+  int64_t gcScanStep(int64_t fuel) {
     Node *n = firstGeq(root, removalKey).n;
     // There's no way to erase removalKey without introducing a key after it
     assert(n != nullptr);
@@ -2893,7 +2879,7 @@ struct __attribute__((visibility("hidden"))) ConflictSet::Impl {
     if (n == root) {
       n = nextPhysical(n);
     }
-    for (; keyUpdates > 0 && n != nullptr; --keyUpdates) {
+    for (; fuel > 0 && n != nullptr; --fuel) {
       if (n->entryPresent && std::max(n->entry.pointVersion,
                                       n->entry.rangeVersion) <= oldestVersion) {
         // Any transaction n would have prevented from committing is
@@ -2915,6 +2901,24 @@ struct __attribute__((visibility("hidden"))) ConflictSet::Impl {
       removalKeyArena = Arena();
       removalKey = getSearchPath(removalKeyArena, n);
     }
+    return fuel;
+  }
+
+  void setOldestVersion(int64_t o) {
+    InternalVersionT oldestVersion{o};
+    assert(o >= oldestVersionFullPrecision);
+    this->oldestVersionFullPrecision = o;
+    this->oldestVersion = oldestVersion;
+    InternalVersionT::zero = oldestVersion;
+#ifdef NDEBUG
+    // This is here for performance reasons, since we want to amortize the cost
+    // of storing the search path as a string. In tests, we want to exercise the
+    // rest of the code often.
+    if (keyUpdates < 100) {
+      return;
+    }
+#endif
+    keyUpdates = gcScanStep(keyUpdates);
   }
 
   explicit Impl(int64_t oldestVersion)