fix(#38): break Transaction<->Snapshot reference cycle - #78
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Transaction::snapshot() cached the Snapshot on the parent transaction, closing a reference cycle (Transaction -> snapshotInstance -> Snapshot -> parentTransaction) that kept both objects alive by refcount and deferred fdb_transaction_destroy() to the cycle collector - or to process shutdown when zend.enable_gc=0. Long-running workers calling readTransact(), directory operations (HighContentionAllocator) or Locality accumulated undestroyed native transaction handles. snapshot() now returns a fresh Snapshot per call. The Snapshot still anchors its parent one-directionally, so the shared native handle stays valid for the snapshot's lifetime and both are freed deterministically on scope exit. - Unit: tests/Unit/SnapshotLifetimeTest.php (native-free, reflection- built; asserts fresh instance per call, anchor semantics, and refcount-only destruction without gc_collect_cycles) - Integration: tests/Integration/TransactionLifecycleTest.php (weak-ref loop over createTransaction+snapshot; directory creation leaves no cyclic garbage). Both fail against the previous implementation. - Docs: snapshot lifetime/ownership notes in docs/transactions.md
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Readonly properties may only be reflection-initialized from their declaring class scope; on PHP < 8.4 a subclass scope (Transaction for props declared on ReadTransaction) is rejected. Resolve the ReflectionProperty against ReadTransaction::class explicitly.
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Closes #38
Problem
Transaction::snapshot()cached theSnapshotinstance on the parent transaction:Transaction -> $snapshotInstance -> Snapshot -> $parentTransaction -> TransactionBoth sides held strong references, so refcounts never reached zero on scope exit and
Transaction::__destruct()(i.e.fdb_transaction_destroy()) only ran via the cyclecollector — or at process shutdown when
zend.enable_gc=0. The cycle was created onevery
snapshot()call:Database::readTransact(), everyHighContentionAllocator::allocate()(i.e. every directory create/open), and
Locality. A long-running worker thereforeaccumulated undestroyed native FDB transaction handles.
Change
snapshot()now returns a freshSnapshotper call (as proposed in the issue).The
Snapshotstill anchors its parent one-directionally, so the shared native handleremains valid for the snapshot's lifetime; once both go out of scope, destruction is
deterministic by refcounting alone. Read-only semantics are unchanged.
Verification
composer lint(PHPCS + Rector + PHPStan L9)composer test:unitNew tests:
tests/Unit/SnapshotLifetimeTest.php— native-free (reflection-built objects, types-only FFI scope): fresh instance per call, snapshot anchors parent, deterministic destruction withoutgc_collect_cycles(), destructor-run observable.tests/Integration/TransactionLifecycleTest.php— weak-ref loop overcreateTransaction()+snapshot()+getReadVersion(); directory creation loop leaves zero cyclic garbage.Docs: lifetime/ownership notes added to
docs/transactions.md. Changelog entry added under[Unreleased] → Fixed.