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#include "CursorManager.h"
#include "Merkle.h"
#include "ObjectManager.h"
#include "TupleCodec.h"
namespace nt {
CursorManager::CursorManager(IStorageBackend& backend, LifecycleManager* lifecycles,
ObjectManager* objects)
: backend_(backend), lifecycles_(lifecycles), objects_(objects) {
}
// Finds the /system/snapshots/<H> entry that owns a handle's relation, or
// nullptr when the relation lives outside the snapshot namespace (tests use
// synthetic paths like {"relations", "villager"}).
static ObjectManager::registry* find_parent_snapshot(ObjectManager& objects,
HandlerManager::handle* handle) {
if (handle == nullptr || handle->object == nullptr || handle->object->head == nullptr)
return nullptr;
const auto& p = handle->object->head->path;
if (p.size() != 5)
return nullptr;
if (p[0] != "system" || p[1] != "snapshots" || p[3] != "relations")
return nullptr;
return objects.Find({p[0], p[1], p[2]});
}
void CursorManager::LoadPage(cursor* c) {
auto entries = Merkle<Hash32>::Page(backend_, c->merkle_root, c->fetch_offset, PAGE_SIZE);
c->page.clear();
c->page_position = 0;
for (const auto& entry : entries) {
auto bytes = backend_.Get(bin_to_hex(entry.payload));
if (!bytes)
continue;
c->page.emplace_back(TupleCodec::Deserialize(*bytes));
}
c->fetch_offset += entries.size();
if (entries.size() < PAGE_SIZE)
c->exhausted = true;
}
CursorManager::cursor* CursorManager::Open(HandlerManager::handle* handle,
const std::string& merkle_root) {
if (handle == nullptr || handle->object == nullptr)
return nullptr;
const auto label = handle->object->head->type->label;
auto pin_snapshot = [&](cursor* c) {
if (lifecycles_ == nullptr || objects_ == nullptr)
return;
auto* snap = find_parent_snapshot(*objects_, handle);
if (snap == nullptr)
return;
lifecycles_->Pin(snap);
c->pinned_snapshot = snap;
};
if (label == EPHEMERAL_RELATION) {
// Cursor is created exhausted — the JOIN operator writes args and
// resets the state before the first probe. The generator is copied
// off the registry-owned ephemeral_object_type so Next() never has
// to dereference the handle again.
auto* etype = static_cast<ObjectManager::ephemeral_object_type*>(
handle->object->head->type.get());
auto* c = new cursor();
c->is_ephemeral = true;
c->generator = etype->generator;
c->exhausted = true;
pin_snapshot(c);
return c;
}
if (label != RELATION)
return nullptr;
auto* c = new cursor();
c->merkle_root = merkle_root;
pin_snapshot(c);
if (merkle_root.empty()) {
// Empty relation: valid but immediately exhausted.
c->exhausted = true;
return c;
}
LoadPage(c);
return c;
}
Tuple* CursorManager::Next(cursor* c) {
if (c == nullptr)
return nullptr;
if (c->page_position < c->page.size())
return &c->page[c->page_position++];
if (c->exhausted)
return nullptr;
if (c->is_ephemeral) {
c->page = c->generator(c->args, c->fetch_offset, PAGE_SIZE);
c->page_position = 0;
c->fetch_offset += c->page.size();
if (c->page.size() < PAGE_SIZE)
c->exhausted = true;
if (c->page.empty())
return nullptr;
return &c->page[c->page_position++];
}
LoadPage(c);
if (c->page.empty())
return nullptr;
return &c->page[c->page_position++];
}
void CursorManager::Close(cursor* c) {
if (c == nullptr) {
return;
}
if (lifecycles_ != nullptr && c->pinned_snapshot != nullptr)
lifecycles_->Unpin(c->pinned_snapshot);
delete c;
}
} // namespace nt
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