weaselab/versioned-map
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Fix two node-copying bugs in update

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This commit is contained in:
Andrew Noyes
2024-05-14 17:44:01 -07:00
parent 862fc3297c
commit 67c8ca8f3a
4 changed files with 74 additions and 17 deletions
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26
VersionedMap.cpp
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@@ -638,7 +638,8 @@ struct __attribute__((__visibility__("hidden"))) VersionedMap::Impl {
auto &c = mm.base[copy];
c.entry = n.entry->addref();
c.pointer[which] = child;
c.pointer[!which] = n.pointer[!which];
c.pointer[!which] =
this->child<std::memory_order_relaxed>(node, !which, latestVersion);
c.updated.store(false, std::memory_order_relaxed);
c.updateVersion = version;
assert(copy == 0 || copy >= kMinAddressable);
@@ -649,11 +650,12 @@ struct __attribute__((__visibility__("hidden"))) VersionedMap::Impl {
// The reason these aren't data races is that concurrent readers are
// reading < `version`
if (updated && n.replacedPointer != which) {
auto result = doCopy();
// We can't update n.replacedPointer without introducing a data race
// (unless we packed it into the atomic?) so we copy. pointer[2] becomes
// unreachable, but need to tell the garbage collector.
n.pointer[2] = 0;
return doCopy();
return result;
} else if (updated) {
n.pointer[2] = child;
} else {
@@ -808,12 +810,13 @@ struct __attribute__((__visibility__("hidden"))) VersionedMap::Impl {
void remove(Finger &finger) {
#ifndef NDEBUG
uint32_t expected;
Entry *expected;
{
Finger copy;
finger.copyTo(copy);
move<std::memory_order_relaxed>(copy, latestVersion, true);
expected = copy.searchPathSize() > 0 ? copy.backNode() : 0;
expected =
copy.searchPathSize() > 0 ? mm.base[copy.backNode()].entry : nullptr;
}
#endif
@@ -850,7 +853,7 @@ struct __attribute__((__visibility__("hidden"))) VersionedMap::Impl {
// propagate up the search path, all the way to the root since we may have
// more rotations to do even if an update doesn't change a node pointer
auto node = finger.backNode();
const auto oldSize = finger.searchPathSize();
const auto oldSize = finger.searchPathSize() - (node == 0);
for (;;) {
if (finger.searchPathSize() == 1) {
// Made it to the root
@@ -873,12 +876,17 @@ struct __attribute__((__visibility__("hidden"))) VersionedMap::Impl {
finger.push(c, false);
}
} else {
move<std::memory_order_relaxed>(finger, latestVersion, true);
while (finger.searchPathSize() > 1 && finger.backDirection() == true) {
finger.pop();
}
finger.pop();
}
#ifndef NDEBUG
if (finger.searchPathSize() > 0) {
assert(finger.backNode() == expected);
assert(mm.base[finger.backNode()].entry == expected);
} else {
assert(expected == nullptr);
}
#endif
}
@@ -1342,7 +1350,7 @@ void VersionedMap::Impl::printInOrderHelper(int64_t version, uint32_t node,
return;
}
printInOrderHelper(version,
child<std::memory_order_relaxed>(node, false, version),
child<std::memory_order_relaxed>(node, true, version),
depth + 1);
for (int i = 0; i < depth; ++i) {
printf(" ");
@@ -1360,7 +1368,7 @@ void VersionedMap::Impl::printInOrderHelper(int64_t version, uint32_t node,
}
printf("\n");
VersionedMap::Impl::printInOrderHelper(
version, child<std::memory_order_relaxed>(node, true, version),
version, child<std::memory_order_relaxed>(node, false, version),
depth + 1);
}