Package com.google.adk.flows.llmflows

Class PersistBarrier

java.lang.Object

com.google.adk.flows.llmflows.PersistBarrier

public final class PersistBarrier
extends Object

Lets BaseLlmFlow's multi-step loop wait until the Runner -- the sole event persister -- has appended the current step's events, so the next step's request (built from session.events() by Contents) is not assembled from a stale session. The Runner calls markPersisted(com.google.adk.agents.InvocationContext, java.lang.String) (or markFailed(com.google.adk.agents.InvocationContext, java.lang.String, java.lang.Throwable)) after each append; the flow calls awaitPersisted(com.google.adk.agents.InvocationContext, java.util.List<com.google.adk.events.Event>) between steps. State lives in the per-invocation InvocationContext.callbackContextData() map, shared across the agent tree.

Each event id maps to a CompletableSubject: pending until its append finishes, then terminally completed or failed. The subject retains its terminal state, so awaitPersisted/mark* may happen in any order and a late await -- e.g. at a higher flow level across an agent transfer -- resolves immediately. If an append fails, the matching await fails with that error rather than blocking forever.

Thread-safe and lock-free: markPersisted/markFailed may run off-thread (async appendEvent) concurrently with awaitPersisted; ConcurrentHashMap.computeIfAbsent(K, java.util.function.Function<? super K, ? extends V>) hands both sides the same subject, which itself serializes its terminal signal against subscription.

Method Summary

Modifier and Type	Method	Description
static io.reactivex.rxjava3.core.Completable	awaitPersisted(InvocationContext context, List<Event> events)	Completes once every event in events has been markPersisted(com.google.adk.agents.InvocationContext, java.lang.String), or fails if any was markFailed(com.google.adk.agents.InvocationContext, java.lang.String, java.lang.Throwable); completes immediately if the barrier was never enable(com.google.adk.agents.InvocationContext)d.
static void	enable(InvocationContext context)	Marks that a Runner is driving this invocation and will resolve each appended event.
static void	markFailed(InvocationContext context, String eventId, Throwable error)	Signals that persisting the event with the given id failed, so an await on it fails with error instead of blocking forever.
static void	markPersisted(InvocationContext context, String eventId)	Signals that the Runner persisted the event with the given id.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method Details

enable

public static void enable(InvocationContext context)

Marks that a Runner is driving this invocation and will resolve each appended event. Otherwise (flow run directly, e.g. unit tests) awaitPersisted(com.google.adk.agents.InvocationContext, java.util.List<com.google.adk.events.Event>) is a no-op, avoiding a deadlock waiting for a signal that never comes.

awaitPersisted

public static io.reactivex.rxjava3.core.Completable awaitPersisted(InvocationContext context,
 List<Event> events)

Completes once every event in events has been markPersisted(com.google.adk.agents.InvocationContext, java.lang.String), or fails if any was markFailed(com.google.adk.agents.InvocationContext, java.lang.String, java.lang.Throwable); completes immediately if the barrier was never enable(com.google.adk.agents.InvocationContext)d. Already-resolved events resolve immediately, so the order of awaitPersisted/ mark* does not matter.

markPersisted

public static void markPersisted(InvocationContext context,
 String eventId)

Signals that the Runner persisted the event with the given id.

markFailed

public static void markFailed(InvocationContext context,
 String eventId,
 Throwable error)

Signals that persisting the event with the given id failed, so an await on it fails with error instead of blocking forever.