Branching and object registry rework (#11)

1 files changed, 69 insertions, 6 deletions

diff --git a/include/LifecycleManager.h b/include/LifecycleManager.h
index 8126820..5508bc6 100644
--- a/include/LifecycleManager.h
+++ b/include/LifecycleManager.h
@@ -1,6 +1,7 @@
 #pragma once
 
 #include "Api.h"
+#include "IStorageBackend.h"
 #include "ObjectManager.h"
 
 /**
@@ -15,9 +16,9 @@ namespace nt
      *
      * Object lifetime is governed by two independent counters in registry_head:
      * `handle_count` (sessions holding an open handle) and `reference_count`
-     * (structural dependencies such as cursors pinned to a snapshot or views
-     * referencing base relations). An object is eligible for GC only when both
-     * reach zero.
+     * (structural dependencies such as cursors pinned to a snapshot or
+     * ephemeral relations referencing their base relations). An object is
+     * eligible for GC only when both reach zero.
      *
      * Monitor / Unmonitor manage `handle_count`. Pin / Unpin manage
      * `reference_count`. See docs/reactos-ob-comparison.md §1.
@@ -26,6 +27,18 @@ namespace nt
     {
     public:
         /**
+         * @brief Constructs a LifecycleManager bound to a registry and store.
+         *
+         * Needs the registry to perform GC: Unmonitor and Unpin call
+         * ObjectManager::Unregister once both counters reach zero. Type-specific
+         * cleanup (e.g. cascading a Multigroup's pin to its child Relations,
+         * or a BranchTree's pin to its child Multigroups) runs inside the
+         * lifecycle manager before the entry is spliced out. The storage
+         * backend is needed by CascadeBranchTree to page the merkle nodes.
+         */
+        LifecycleManager(ObjectManager& objects, IStorageBackend& storage);
+
+        /**
          * @brief Starts monitoring an object's lifecycle.
          *
          * Increments `handle_count` on the object's registry_head. Should be
@@ -53,9 +66,9 @@ namespace nt
          * @brief Increments the structural dependency count on an object.
          *
          * Call when one object takes a dependency on another — for example when
-         * a cursor pins an immutable snapshot version, or when a view is
-         * registered against its base relations. Prevents GC of the target object
-         * while the dependency is live.
+         * a cursor pins an immutable snapshot version, or when an ephemeral
+         * relation is registered against its base relations. Prevents GC of the
+         * target object while the dependency is live.
          *
          * @todo Implement. See docs/reactos-ob-comparison.md §1.
          *
@@ -76,6 +89,15 @@ namespace nt
         void Unpin(ObjectManager::registry* object);
 
         /**
+         * @brief Returns true when the object is GC-eligible right now.
+         *
+         * Eligibility is the joint condition handle_count == 0 &&
+         * reference_count == 0. Decrement callers (Unmonitor / Unpin) consult
+         * this and, when true, run type-specific cleanup before unregistering.
+         */
+        bool IsEligibleForGC(ObjectManager::registry* object) const;
+
+        /**
          * @brief Serializes contention for changes to mutable reference states.
          *
          * Immutable objects — relation snapshots, multigroup snapshots,
@@ -97,5 +119,46 @@ namespace nt
          * @return True when the operation may proceed.
          */
         const bool Contention(ObjectManager::registry* object);
+
+    private:
+        /**
+         * @brief Joint-counters check + type-specific cascade + Unregister.
+         *
+         * Called by Unmonitor and Unpin after their decrement. No-op when the
+         * object is still referenced. When eligible:
+         *   - MULTIGROUP entries first unpin every Relation registered as a
+         *     direct child of their /system/snapshots/H subtree.
+         *   - BRANCH_TREE entries first unpin every Multigroup their
+         *     content-addressed tree references.
+         *   - The entry is then removed from the registry; its IObject and
+         *     registry_head are freed.
+         *
+         * Inline GC for now; the reaper-queue deferred-deletion pattern from
+         * docs/reactos-ob-comparison.md §7 is a later optimisation.
+         */
+        void TryCollect(ObjectManager::registry* object);
+
+        /**
+         * @brief Releases pins held by a MULTIGROUP entry on its child Relations.
+         *
+         * Iterates the registry once, collects every /system/snapshots/<H>/<n>
+         * direct child, and calls Unpin on each. Triggered exclusively from
+         * TryCollect at the moment the parent snapshot becomes eligible for GC.
+         */
+        void CascadeMultigroup(ObjectManager::registry* multigroup);
+
+        /**
+         * @brief Releases pins held by a BRANCH_TREE entry on its child mgs.
+         *
+         * Pages the Merkle<std::string> tree at the BranchTree's merkle_root,
+         * resolves each (mg_name, mg_hash) entry to its
+         * /system/snapshots/<mg_hash> Multigroup, and calls Unpin on it.
+         * Triggered exclusively from TryCollect at the moment the BranchTree
+         * itself becomes eligible for GC.
+         */
+        void CascadeBranchTree(ObjectManager::registry* branch_tree);
+
+        ObjectManager&   objects_;
+        IStorageBackend& storage_;
     };
 }