Implement Remote Persistent Workers

deployment-examples/persistent-workers/README.md

@@ -0,0 +1,21 @@
+# Persistent Worker Examples
+
+These examples show the NativeLink-facing part of Bazel actions that opt in to
+remote persistent worker execution.
+
+Persistent workers are useful for JVM-heavy tools such as `javac`, `scalac`, and
+`kotlinc`, and for worker wrappers around tools such as `tsc`. Compatible
+actions declare worker support with execution requirements:
+
+```starlark
+execution_requirements = {
+    "supports-workers": "1",
+    "requires-worker-protocol": "proto",  # or "json"
+}
+```
+
+See:
+
+- [Java](./java/README.md)
+- [TypeScript](./typescript/README.md)
+- [Kotlin](./kotlin/README.md)

deployment-examples/persistent-workers/java/README.md

@@ -0,0 +1,28 @@
+# Java Persistent Worker Example
+
+This example shows the NativeLink-facing part of a Java compile action that can
+run through the remote persistent worker path. The action must declare that the
+tool supports Bazel's worker protocol and that it uses the proto wire format.
+
+```starlark
+def _javac_worker_impl(ctx):
+    args = ctx.actions.args()
+    args.add("@%s" % ctx.outputs.argfile.path)
+
+    ctx.actions.run(
+        executable = ctx.executable.javac_worker,
+        arguments = [args],
+        inputs = ctx.files.srcs + [ctx.outputs.argfile],
+        outputs = [ctx.outputs.jar],
+        mnemonic = "Javac",
+        execution_requirements = {
+            "supports-workers": "1",
+            "requires-worker-protocol": "proto",
+        },
+    )
+```
+
+NativeLink computes the `WorkerKey` from the executable, startup flags before the
+first `@argfile`, and `requires-worker-protocol`. The first action starts
+`javac_worker --persistent_worker`; later compatible actions send `WorkRequest`
+messages to the same process.

deployment-examples/persistent-workers/kotlin/README.md

@@ -0,0 +1,25 @@
+# Kotlin Persistent Worker Example
+
+Kotlin compile actions have the same remote execution shape as Java: keep the JVM
+compiler process warm and send per-action argument files through the worker protocol.
+
+```starlark
+def _kotlinc_worker_impl(ctx):
+    args = ctx.actions.args()
+    args.add("@%s" % ctx.outputs.argfile.path)
+
+    ctx.actions.run(
+        executable = ctx.executable.kotlinc_worker,
+        arguments = [args],
+        inputs = ctx.files.srcs + [ctx.outputs.argfile],
+        outputs = [ctx.outputs.jar],
+        mnemonic = "KotlinCompile",
+        execution_requirements = {
+            "supports-workers": "1",
+            "requires-worker-protocol": "proto",
+        },
+    )
+```
+
+The worker process is started once with `--persistent_worker`; compatible Kotlin
+compile actions reuse it until the pool idle timeout or request cap retires it.

deployment-examples/persistent-workers/typescript/README.md

@@ -0,0 +1,27 @@
+# TypeScript Persistent Worker Example
+
+TypeScript worker wrappers commonly use JSON worker protocol framing. The
+important NativeLink requirement is that the remote action advertises both
+worker support and the JSON protocol.
+
+```starlark
+def _tsc_worker_impl(ctx):
+    args = ctx.actions.args()
+    args.add("@%s" % ctx.outputs.tsconfig.path)
+
+    ctx.actions.run(
+        executable = ctx.executable.tsc_worker,
+        arguments = [args],
+        inputs = ctx.files.srcs + [ctx.outputs.tsconfig],
+        outputs = ctx.outputs.js,
+        mnemonic = "TypeScriptCompile",
+        execution_requirements = {
+            "supports-workers": "1",
+            "requires-worker-protocol": "json",
+        },
+    )
+```
+
+The persistent worker should read one newline-delimited JSON `WorkRequest` from
+`stdin` and emit one newline-delimited JSON `WorkResponse` to `stdout` for each
+action.

nativelink-scheduler/src/simple_scheduler_state_manager.rs

@@ -354,6 +354,20 @@ where
 
         let now = (self.now_fn)().now();
 
+        // Honor the per-action `Action.timeout` from the RBE protocol as a
+        // backend wall-clock deadline. Without this, the only enforcement is
+        // the Bazel client's --test_timeout, which surfaces as TIMEOUT/NO
+        // STATUS instead of a backend signal pointing at the worker.
+        let action_timeout = awaited_action.action_info().timeout;
+        if action_timeout > Duration::ZERO {
+            let executing_started_at = awaited_action.state().last_transition_timestamp;
+            if let Ok(elapsed) = now.duration_since(executing_started_at)
+                && elapsed > action_timeout
+            {
+                return true;
+            }
+        }
+
         let registry_alive = if let Some(ref worker_registry) = self.worker_registry {
             if let Some(worker_id) = awaited_action.worker_id() {
                 worker_registry
@@ -785,7 +799,37 @@ where
                         ActionStage::Queued
                     }
                 }
-                UpdateOperationType::UpdateWithDisconnect => ActionStage::Queued,
+                UpdateOperationType::UpdateWithDisconnect => {
+                    // A worker disconnect (e.g. OOMKill, pod eviction, network
+                    // drop) used to requeue without counting as an attempt,
+                    // which let an action that always crashes its worker loop
+                    // forever until the Bazel client's --test_timeout fired.
+                    // Count disconnects as attempts so max_job_retries caps the
+                    // loop and the client sees a backend-attributable error.
+                    awaited_action.attempts += 1;
+
+                    if awaited_action.attempts > self.max_job_retries {
+                        ActionStage::Completed(ActionResult {
+                            execution_metadata: ExecutionMetadata {
+                                worker: maybe_worker_id
+                                    .map_or_else(String::default, ToString::to_string),
+                                ..ExecutionMetadata::default()
+                            },
+                            error: Some(make_err!(
+                                Code::Internal,
+                                "Worker disconnected repeatedly while executing this action ({} > {} attempts); the runner likely OOMKilled or the pod was evicted. {}",
+                                awaited_action.attempts,
+                                self.max_job_retries,
+                                format!(
+                                    "for operation_id: {operation_id}, maybe_worker_id: {maybe_worker_id:?}"
+                                ),
+                            )),
+                            ..ActionResult::default()
+                        })
+                    } else {
+                        ActionStage::Queued
+                    }
+                }
                 // We shouldn't get here, but we just ignore it if we do.
                 UpdateOperationType::ExecutionComplete => {
                     warn!("inner_update_operation got an ExecutionComplete, that's unexpected.");

nativelink-scheduler/tests/simple_scheduler_test.rs

@@ -2116,6 +2116,182 @@ async fn worker_retries_on_internal_error_and_fails_test() -> Result<(), Error>
     Ok(())
 }
 
+/// Worker crash-loop regression: an action whose worker keeps disconnecting
+/// (e.g. `OOMKill`) used to bypass `max_job_retries` because
+/// `UpdateWithDisconnect` requeued without counting as an attempt. The build
+/// would only terminate when the Bazel client's `--test_timeout` fired,
+/// hiding the cluster-side root cause behind a TIMEOUT/NO STATUS surface.
+/// After the fix, disconnects count as attempts and exceed the cap.
+#[nativelink_test]
+async fn worker_disconnect_loop_caps_at_max_job_retries_test() -> Result<(), Error> {
+    let worker_id = WorkerId("worker_id".to_string());
+
+    let task_change_notify = Arc::new(Notify::new());
+    let (scheduler, _worker_scheduler) = SimpleScheduler::new_with_callback(
+        &SimpleSpec {
+            max_job_retries: 1,
+            ..Default::default()
+        },
+        memory_awaited_action_db_factory(
+            0,
+            &task_change_notify.clone(),
+            MockInstantWrapped::default,
+        ),
+        || async move {},
+        task_change_notify,
+        MockInstantWrapped::default,
+        None,
+    );
+    let action_digest = DigestInfo::new([99u8; 32], 512);
+
+    let mut rx_from_worker =
+        setup_new_worker(&scheduler, worker_id.clone(), PlatformProperties::default()).await?;
+    let insert_timestamp = make_system_time(1);
+    let mut action_listener =
+        setup_action(&scheduler, action_digest, HashMap::new(), insert_timestamp).await?;
+
+    let operation_id = {
+        let operation_id = match rx_from_worker.recv().await.unwrap().update {
+            Some(update_for_worker::Update::StartAction(exec)) => exec.operation_id,
+            v => panic!("Expected StartAction, got : {v:?}"),
+        };
+        assert_eq!(
+            action_listener.changed().await.unwrap().0.stage,
+            ActionStage::Executing
+        );
+        OperationId::from(operation_id.as_str())
+    };
+
+    // First disconnect: should requeue (attempts=1, not yet > max_job_retries=1).
+    drop(
+        scheduler
+            .update_action(
+                &worker_id,
+                &operation_id,
+                UpdateOperationType::UpdateWithDisconnect,
+            )
+            .await,
+    );
+    {
+        let (action_state, _maybe_origin_metadata) = action_listener.changed().await.unwrap();
+        assert_eq!(
+            action_state.stage,
+            ActionStage::Queued,
+            "First disconnect should requeue, got: {:?}",
+            action_state.stage,
+        );
+    }
+
+    // Reattach worker so it picks up the requeued action.
+    let mut rx_from_worker =
+        setup_new_worker(&scheduler, worker_id.clone(), PlatformProperties::default()).await?;
+    {
+        match rx_from_worker.recv().await.unwrap().update {
+            Some(update_for_worker::Update::StartAction(_)) => { /* Success */ }
+            v => panic!("Expected StartAction, got : {v:?}"),
+        }
+        assert_eq!(
+            action_listener.changed().await.unwrap().0.stage,
+            ActionStage::Executing
+        );
+    }
+
+    // Second disconnect: now attempts=2 > max_job_retries=1, so the action
+    // must transition to Completed with an error mentioning the disconnect
+    // loop, not silently requeue.
+    drop(
+        scheduler
+            .update_action(
+                &worker_id,
+                &operation_id,
+                UpdateOperationType::UpdateWithDisconnect,
+            )
+            .await,
+    );
+    {
+        let (action_state, _maybe_origin_metadata) = action_listener.changed().await.unwrap();
+        let ActionStage::Completed(action_result) = &action_state.stage else {
+            panic!(
+                "Second disconnect should mark action Completed-with-error, got: {:?}",
+                action_state.stage
+            );
+        };
+        let err = action_result
+            .error
+            .as_ref()
+            .expect("Completed action from disconnect cap must carry an error");
+        assert!(
+            err.to_string()
+                .contains("Worker disconnected repeatedly while executing this action"),
+            "Error message did not mention disconnect loop: {err}",
+        );
+    }
+
+    Ok(())
+}
+
+/// `Action.timeout` from the RBE protocol must be enforced backend-side.
+/// Without this, an action that hangs forever only terminates when the
+/// Bazel client's `--remote_timeout` (gRPC deadline) or `--test_timeout`
+/// (client-side) fires; from the operator's perspective the cluster never
+/// surfaces the slow action.
+#[nativelink_test]
+async fn action_timeout_is_enforced_backend_side_test() -> Result<(), Error> {
+    use nativelink_scheduler::awaited_action_db::AwaitedAction;
+    use nativelink_scheduler::simple_scheduler_state_manager::SimpleSchedulerStateManager;
+
+    // Anchor MockClock so MockInstantWrapped::now() == make_system_time(0).
+    MockClock::set_time(Duration::from_secs(NOW_TIME));
+    let executing_started_at = make_system_time(0);
+
+    let action_digest = DigestInfo::new([7u8; 32], 1);
+    let mut action_info = make_base_action_info(executing_started_at, action_digest);
+    Arc::make_mut(&mut action_info).timeout = Duration::from_secs(2);
+
+    let operation_id = OperationId::default();
+    let mut awaited_action =
+        AwaitedAction::new(operation_id.clone(), action_info, executing_started_at);
+    awaited_action.worker_set_state(
+        Arc::new(ActionState {
+            stage: ActionStage::Executing,
+            client_operation_id: operation_id,
+            action_digest,
+            last_transition_timestamp: executing_started_at,
+        }),
+        executing_started_at,
+    );
+
+    let task_change_notify = Arc::new(Notify::new());
+    let state_mgr = SimpleSchedulerStateManager::new(
+        /* max_job_retries */ 1,
+        /* no_event_action_timeout */ Duration::from_secs(60),
+        /* client_action_timeout */ Duration::from_secs(60),
+        /* max_executing_timeout */ Duration::ZERO,
+        memory_awaited_action_db_factory(
+            0,
+            &task_change_notify.clone(),
+            MockInstantWrapped::default,
+        ),
+        MockInstantWrapped::default,
+        /* worker_registry */ None,
+    );
+
+    assert!(
+        !state_mgr.should_timeout_operation(&awaited_action).await,
+        "Should not time out before Action.timeout elapses",
+    );
+
+    // Advance past the 2s per-action deadline.
+    MockClock::advance(Duration::from_secs(5));
+
+    assert!(
+        state_mgr.should_timeout_operation(&awaited_action).await,
+        "Scheduler must mark Executing action timed out once Action.timeout has elapsed",
+    );
+
+    Ok(())
+}
+
 #[nativelink_test]
 async fn ensure_scheduler_drops_inner_spawn() -> Result<(), Error> {
     struct DropChecker {

nativelink-worker/BUILD.bazel

@@ -13,6 +13,10 @@ rust_library(
         "src/directory_cache.rs",
         "src/lib.rs",
         "src/local_worker.rs",
+        "src/persistent_worker/live_worker.rs",
+        "src/persistent_worker/mod.rs",
+        "src/persistent_worker/pool.rs",
+        "src/persistent_worker/protocol.rs",
         "src/qos.rs",
         "src/running_actions_manager.rs",
         "src/worker_api_client_wrapper.rs",
@@ -43,6 +47,7 @@ rust_library(
         "@crates//:relative-path",
         "@crates//:scopeguard",
         "@crates//:serde",
+        "@crates//:serde_json",
         "@crates//:serde_json5",
         "@crates//:shlex",
         "@crates//:tokio",
@@ -116,6 +121,8 @@ rust_test(
         "@crates//:hyper",
         "@crates//:pretty_assertions",
         "@crates//:prost-types",
+        "@crates//:rand",
+        "@crates//:serde_json",
         "@crates//:serial_test",
         "@crates//:tempfile",
         "@crates//:tracing-test",

nativelink-worker/Cargo.toml

@@ -31,7 +31,10 @@ relative-path = { version = "2.0.0", default-features = false, features = [
   "std",
 ] }
 scopeguard = { version = "1.2.0", default-features = false }
-serde = { version = "1.0.219", default-features = false }
+serde = { version = "1.0.219", default-features = false, features = ["derive"] }
+serde_json = { version = "1.0.140", default-features = false, features = [
+  "std",
+] }
 serde_json5 = { version = "0.2.1", default-features = false }
 shlex = { version = "2.0.0", default-features = false }
 tokio = { version = "1.52.2", features = [