Add cancellation and deadline support to Session.process_request

[bmehta001]

Summary

Adds invocation-scoped cancellation and timeouts for synchronous inference without introducing a separate operation API.

• Request.Cancel() targets only the active invocation, interrupts its ORT GenAI generator, and is a no-op while idle.
• Each ProcessRequest call gets a fresh wall-clock deadline covering native admission and inference.
• Session.Cancel() permanently cancels active and queued calls and rejects later processing on that Session.
• Chat and audio remain serialized with cancellable admission; distinct embeddings Requests remain concurrent and cancel independently.
• C#, JavaScript, and Python expose the same processing behavior and keep native Request/Session handles alive until inference exits.

Results

Cause	Result
Request.Cancel()	Active call returns FOUNDRY_LOCAL_ERROR_OPERATION_CANCELLED; later sequential reuse is supported
Timeout	Active call returns FOUNDRY_LOCAL_ERROR_TIMEOUT; the next call starts a new deadline
Session.Cancel()	Active/queued calls are cancelled; later calls return FOUNDRY_LOCAL_ERROR_INVALID_USAGE
Streaming callback returns nonzero	Cooperative successful stop with FOUNDRY_LOCAL_FINISH_NONE

Cancellation, timeout, callback stop, completion, and failure use one first-winner invocation outcome. Cancelled or timed-out chat turns are not committed to history. Cooperative callback stop rewinds the uncommitted turn; hard engine interruption discards the generator so the next call rebuilds from committed history. Embeddings responses remain all-or-nothing.

Assumptions and deferrals

• A Request is used by one invocation at a time. Sequential reuse is supported; overlapping use is not runtime-enforced.
• Admission order is unspecified.
• Timeout does not include time spent in a managed SDK worker queue before entering native ProcessRequest.
• The C ABI is unpublished, so this initial release keeps API version 1 while tail-appending the new functions.
• No public operation handle or shared deadline scheduler is added.

Validation

• Focused native cancellation and generator-lifetime tests pass on Windows and Linux, including repeated shuffled runs.
• Real streaming-audio cancellation passes on Windows, Linux, and macOS packaging CI.
• C#, JavaScript, and Python cancellation/lifetime suites pass on their completed platform jobs.
• CodeQL and all completed packaging checks pass; remaining packaging jobs are still running.

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Project	Deployment	Actions	Updated (UTC)
foundry-local	Ready	Preview	Aug 16, 2026 7:45pm

[Copilot]

Pull request overview

Adds cross-language cancellation and deadline support for synchronous inference, including engine-level interruption and teardown handling.

Changes:

• Adds native session cancellation, request deadlines, and timeout errors.
• Exposes cancellation/timeouts through C++, Python, C#, and JavaScript.
• Adds chat cancellation and deadline regression tests.

Reviewed changes

Copilot reviewed 37 out of 37 changed files in this pull request and generated 16 comments.

Show a summary per file

File	Description
sdk_v2/python/src/foundry_local_sdk/session.py	Adds timeout, cancellation, and teardown signaling.
sdk_v2/python/src/foundry_local_sdk/request.py	Adds request timeout configuration.
sdk_v2/python/src/foundry_local_sdk/_native/build_cffi.py	Extends Python C ABI definitions.
sdk_v2/js/src/session.ts	Adds AbortSignal cancellation and session cancellation.
sdk_v2/js/src/request.ts	Adds request deadlines.
sdk_v2/js/src/detail/native.ts	Extends native TypeScript interfaces.
sdk_v2/js/src/detail/errors.ts	Adds the timeout error code.
sdk_v2/js/native/src/session.h	Declares native cancellation methods.
sdk_v2/js/native/src/session.cc	Implements native session cancellation bindings.
sdk_v2/js/native/src/request.h	Declares native timeout support.
sdk_v2/js/native/src/request.cc	Implements native timeout binding.
sdk_v2/cs/src/Session.cs	Adds token/session cancellation and teardown signaling.
sdk_v2/cs/src/Request.cs	Adds TimeSpan deadlines.
sdk_v2/cs/src/Detail/NativeMethods.cs	Extends C# ABI declarations.
sdk_v2/cs/src/Detail/FoundryLocalApi.cs	Maps timeout errors and session cancellation.
sdk_v2/cpp/test/internal_api/chat/chat_session_test.cc	Adds cancellation and deadline tests.
sdk_v2/cpp/src/inferencing/session/session.h	Defines session cancellation state and watchdog support.
sdk_v2/cpp/src/inferencing/session/session.cc	Implements cancellation, tracking, and deadlines.
sdk_v2/cpp/src/inferencing/session/session_manager.h	Documents process-wide cancellation.
sdk_v2/cpp/src/inferencing/session/session_manager.cc	Cancels sessions during shutdown.
sdk_v2/cpp/src/inferencing/session/request.h	Implements reusable request deadlines.
sdk_v2/cpp/src/inferencing/session/oga_generator_cancellable.h	Declares the OGA cancellation adapter.
sdk_v2/cpp/src/inferencing/session/oga_generator_cancellable.cc	Implements engine termination.
sdk_v2/cpp/src/inferencing/session/live_session_registry.h	Declares live-session tracking.
sdk_v2/cpp/src/inferencing/session/live_session_registry.cc	Implements the live-session registry.
sdk_v2/cpp/src/inferencing/session/cancellable.h	Defines the cancellation interface.
sdk_v2/cpp/src/inferencing/generative/embeddings/embeddings_session.h	Adds request-aware embedding generation.
sdk_v2/cpp/src/inferencing/generative/embeddings/embeddings_session.cc	Adds embedding cancellation checks.
sdk_v2/cpp/src/inferencing/generative/chat/chat_session.cc	Publishes chat generators for cancellation.
sdk_v2/cpp/src/inferencing/generative/chat/chat_generator.h	Makes chat generators cancellable.
sdk_v2/cpp/src/inferencing/generative/audio/audio_session.cc	Adds cancellation throughout audio generation.
sdk_v2/cpp/src/inferencing/generative/audio/audio_generator.h	Makes audio generators cancellable.
sdk_v2/cpp/src/c_api.cc	Implements new C ABI operations.
sdk_v2/cpp/include/foundry_local/foundry_local_cpp.inline.h	Implements C++ wrapper methods.
sdk_v2/cpp/include/foundry_local/foundry_local_cpp.h	Exposes C++ cancellation and deadlines.
sdk_v2/cpp/include/foundry_local/foundry_local_c.h	Extends the public C ABI.
sdk_v2/cpp/CMakeLists.txt	Builds the new cancellation sources.

Suppressed comments (2)

sdk_v2/cpp/src/inferencing/generative/audio/audio_session.cc:604

• This second raw OGA decode loop has the same termination-exception gap: Session::Cancel() now terminates the generator during GenerateNextToken(), but this helper does not catch the expected runtime error. A Nemotron cancellation or deadline can therefore bypass normal cancellation/timeout handling. Handle termination when original_request.ShouldStop() is true and rethrow unrelated engine failures.

  while (!generator.IsDone() && !generator.IsSessionTerminated() && !original_request.ShouldStop()) {

sdk_v2/js/src/session.ts:275

• Request_Cancel only sets the request flag; it never invokes the active generator's Cancel(). Consequently this AbortSignal still waits for an in-progress prefill/decode call and cannot interrupt a non-terminating compute as documented. Moreover, the native cancellation path returns a FINISH_NONE response rather than FOUNDRY_LOCAL_ERROR_OPERATION_CANCELLED, so this promise resolves instead of rejecting. Associate request cancellation with its active generator and define the abort rejection before exposing this option.

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[Copilot]

Pull request overview

Copilot reviewed 54 out of 54 changed files in this pull request and generated no new comments.

Suppressed comments (6)

sdk_v2/python/src/foundry_local_sdk/session.py:485

• _check_open() releases the lifecycle lock before this native call, so _close() can transition to closing, release the native session, and leave this thread calling Session_Cancel with None or a freed pointer. cancel() is explicitly thread-safe and can race teardown; hold an active-call lease around the native call just like process_request() does.
  sdk_v2/python/src/foundry_local_sdk/request.py:138
• A positive timeout below one millisecond is truncated to 0, which disables the deadline even though the API documents that only None and non-positive values disable it. Round positive durations up to the next millisecond so a requested deadline is never silently removed.
  sdk_v2/cs/src/Request.cs:148
• A positive TimeSpan shorter than one millisecond casts to 0, silently disabling the timeout despite the contract saying only zero or negative values disable it. Round positive durations up to one millisecond rather than truncating them.
  sdk_v2/python/src/foundry_local_sdk/session.py:480
• This documentation omits the method's terminal behavior: native Session_Cancel permanently marks the session cancelled, so even an idle call causes every later processing call to fail with invalid usage. State that explicitly; describing only interruption and saying it is safe while idle can lead callers to expect the session remains reusable.
  sdk_v2/cs/src/Session.cs:226
• This public contract does not mention that Cancel() is terminal. The native implementation permanently cancels the session, and subsequent processing calls fail with invalid usage even when Cancel() was invoked while idle. Document that behavior so callers do not expect this to be a reusable, current-operation-only cancellation.
  sdk_v2/js/src/session.ts:308
• The documentation presents this as interruption of current work, but native Session::Cancel() is terminal: calling it while idle still makes all later processing calls fail with FlErrorCode.InvalidUsage. Document the permanent state transition so consumers do not attempt to reuse the session.

[Copilot]

Pull request overview

Copilot reviewed 54 out of 54 changed files in this pull request and generated 1 comment.

Suppressed comments (3)

sdk_v2/js/src/session.ts:285

• This listener has the same queueing race as streaming: an abort can occur before the async worker attaches the request's invocation state, and native Request.Cancel() then intentionally does nothing. Since the listener runs only once, the aborted operation can consume the entire generation before line 289 merely converts its successful result to AbortError. Retry until settlement or have the addon latch cancellation for the queued worker.
  sdk_v2/js/src/session.ts:166
• Request.Cancel() is now an idle no-op, so this one-shot abort can race the queued native worker: if the signal fires after processStreamingRequest returns but before BeginInvocation attaches cancellation state, cancellation is lost and the full inference still runs before JavaScript rejects it. Keep retrying cancellation until the native promise settles, or add a pending-cancellation handshake in the addon.

This issue also appears on line 285 of the same file.
sdk_v2/cs/src/Session.cs:356

• This catch wraps native TimeoutException and direct Request.Cancel()'s OperationCanceledException in FoundryLocalException whenever the linked token itself was not canceled. That makes streaming expose different error types from non-streaming and hides the newly added timeout result. Preserve these two mapped exception types before applying the generic streaming wrapper.

[Copilot]

Pull request overview

Copilot reviewed 59 out of 59 changed files in this pull request and generated 1 comment.

[Copilot]

Pull request overview

Copilot reviewed 58 out of 58 changed files in this pull request and generated no new comments.

Suppressed comments (1)

sdk_v2/cpp/src/inferencing/session/session.cc:272

• Each timed invocation creates a dedicated OS thread and keeps it until the invocation settles. Because embeddings explicitly allow concurrent requests, a burst of timed embedding calls can create one watchdog thread (and stack reservation) per request, exhausting process/thread limits before inference admission provides any backpressure. Please use a shared deadline scheduler/timer queue (or another bounded watchdog mechanism) rather than spawning an unbounded thread per timeout.

  if (timeout.count() > 0) {
    deadline_thread = std::thread(&Session::MonitorDeadline, state, std::ref(logger_), timeout);

[Copilot]

Pull request overview

Copilot reviewed 58 out of 58 changed files in this pull request and generated 2 comments.

Suppressed comments (1)

sdk_v2/cpp/src/inferencing/session/session.cc:98

• The move constructor is declared noexcept, but this allocation and the following registry insertion can both throw (for example std::bad_alloc). Any such failure therefore terminates the process instead of propagating. Either avoid allocating/registering a replacement control for the moved-from object, or remove noexcept consistently from the base and derived move constructors.

  other.control_ = std::make_shared<SessionControl>();

  LiveSessionRegistry::Instance().Add(other.control_);

[Copilot]

Pull request overview

Copilot reviewed 58 out of 58 changed files in this pull request and generated no new comments.

Suppressed comments (3)

sdk_v2/js/src/session.ts:388

• This concurrency guard can mask disposal: after dispose() with an unsettled non-streaming call, a new streaming call throws the generic overlap Error instead of the documented FoundryLocalError with InvalidUsage; a pre-aborted call similarly returns AbortError. Perform the disposed check before these local guards and abort handling.
  sdk_v2/cpp/include/foundry_local/foundry_local_c.h:188
• The new timeout code is not handled by ActionStatusFromException (sdk_v2/cpp/src/telemetry/telemetry.cc:91-100). Any outer ActionTracker that records a timeout therefore reports kFailure instead of kTimeout, even though the session-level tracker distinguishes it. Add the timeout case to the central exception-to-status mapping and cover it with its mapping tests.

  /// The configured timeout elapsed. FOUNDRY_LOCAL_ERROR_OPERATION_CANCELLED indicates explicit cancellation.
  FOUNDRY_LOCAL_ERROR_TIMEOUT = 7,

sdk_v2/js/src/session.ts:328

• Local checks run before the native disposed check. If dispose() is called while a stream is settling, this method rejects with the generic overlap error; with a pre-aborted signal it rejects with AbortError. Both contradict the class contract that every post-disposal call fails with FoundryLocalError/InvalidUsage. Check native.isDisposed() first and surface the documented disposed error before concurrency or signal handling.

This issue also appears on line 385 of the same file.

[bmehta001]

Closing for the upcoming release: we are intentionally deferring non-streaming inference cancellation and the broader streaming/lifetime hardening because the implementation cost and review surface are disproportionate to the release scenarios. We will document the current cancellation limitations briefly and handle the separate three-hour model-download timeout as a focused change.

[bmehta001]

Closing for the upcoming release: we are deferring inference cancellation because the implementation and review surface are disproportionate to the release scenarios. A focused replacement will briefly document the limitation and add a three-hour model-download timeout.