spawn 0.1.2

Background execution for Dart that works everywhere - isolates on native, Web Workers on the web, one API. The missing web half of dart:isolate.

Changelog

0.1.2

• Web: a worker started from inside another worker now resolves its payload against the app's asset base, not the parent worker's directory. Rebuild the calling and nested worker payloads together to get the fix.
• Web: map keys are always plain data, including __proto__ and constructor, so a key can no longer change how a message decodes (for example make a map arrive as an array or typed buffer). Maps whose keys collide with spawn's internal markers are escaped. Rebuild and deploy host and worker payloads together: an older decoder cannot read an escaped map.
• New SpawnCaps.isolated: true when the handler runs in its own isolate or Web Worker, false when it runs in process (spawnLocal, the web debug fallback) or the peer is older. Use it to decide whether a worker's cleanup may release process-wide resources.
• spawn:build --target wasm builds Dart WasmGC workers, served from the same .dart.js URL your SpawnEntry declarations already use. Messages sent during startup are queued, a server that does not send the Wasm MIME type still works, and these workers report SpawnPayload.wasm in their capabilities.
• spawn:build --target hybrid ships a WasmGC worker and a JavaScript worker behind one URL: the bootstrap checks for the Wasm features it needs and falls back to JavaScript if startup fails (for example on older iOS browsers). The Wasm-only and JS-only targets remain available.
• New Worker.termination reports how a dedicated worker actually ended, separately from done, which only means the channel closed. On native, WorkerTerminationEvidence.nativeOnExit means the isolate runs no more code; on the web, browserTerminateRequested means the browser accepted terminate(). In-process workers report notStarted. Wait for nativeOnExit before freeing native memory or handles a worker may still be using. A custom host transport can report it by implementing WorkerTerminationTransport.
• A failed start now keeps hold of the worker it began. spawn throws a SpawnStartupException (still a SpawnException) or, on the web when the payload is missing, a SpawnPayloadStartupException (still a SpawnPayloadMissingError), so existing catches keep matching. Both implement the new SpawnStartupFailure: termination, plus a requestStop() that is safe to repeat. A startup timeout no longer counts as the worker having stopped; one stuck in a native call is still running until termination says otherwise. Other errors during startup now arrive wrapped in a SpawnStartupException, with the original as cause.
• SpawnReply takes optional hooks around sending a reply: prepare (may be async, runs before encoding), prepareEncoded and beforeSendEncoded (see the exact encoded reply as a SpawnPreparedReply), and beforeSend (synchronous, just before handoff). Throwing from any of them refuses the reply, and the requester gets the error instead. onSettled runs once the reply is sent or refused, to free data the handler owns; an error thrown there is fatal to the worker.

0.1.1

• Fix: transfer: never transferred on native. Buffers were matched by identity, which never matches on the VM, so payloads were always copied (with correct bytes). They are now matched by backing store.
• Native transfers now look one level into a Map (such as {'rgba': bytes, ...}), as the web backend already did.
• New SpawnReply: a request handler can name buffers to move, rather than copy, in its response. Before, a worker returning a decoded frame paid a full copy on the receiving thread (3.7 MB at 720p).
• Web: a message the worker cannot deserialize no longer vanishes. The browser reports it as a messageerror without data, so the request went unanswered until the host's timeout (seen on iPad with transferred VideoFrames). Every request in flight now fails with the reason, and the worker keeps running.
• Web: an error thrown inside a running worker is no longer dropped. Only startup failures were handled. Now the requests in flight fail with the browser's message, and the worker keeps running.

0.1.0

First release.

• spawn(entry) starts a worker on an isolate (native) or a compiled Web Worker payload (web) behind one API, and completes once the handler is running.
• Worker / WorkerClient: post, request, a broadcast events stream buffered until its first listener, graceful and forced close, and attach() for more clients of one worker.
• WorkerChannel: messages, send, handleRequests, initialMessage, onClose.
• One portability contract everywhere (the portable set, or WireMessage), so a message that works on the VM works in a browser.
• A documented 12-byte wire envelope with a WireRegistry, and SpawnEntry.protocol to register a protocol's decoders on both ends.
• transfer: lists: a real move on the web, and a skipped copy on native for byte payloads. SpawnCaps.zeroCopyTransfer reports which you got.
• SpawnService lifetimes with pluggable, reference-counted ServiceProviders, and an error at spawn time that names a missing registration.
• spawnLocal runs a handler in process behind a real Worker, for tests and as the web debug fallback when a payload has not been built.
• dart run spawn:build compiles lib/workers/*.dart to web payloads, skipping unchanged ones. No code generation and no build_runner. Files without a main are skipped, so helpers and conditional-import stubs can sit next to workers, and the up-to-date check covers path dependencies.
• JobEntry parses and validates; Jobs.enqueue throws until deferred, OS-scheduled work lands.
• SpawnEntry.native is reserved for a C- or wasm-hosted worker and throws.
• PlatformValue carries an opaque platform object (VideoFrame, AudioData, ImageBitmap, OffscreenCanvas) through a channel untouched. It is always transferred, never cloned, including in a request response, since most of these types cannot be cloned; this lets a decode worker hand finished frames to the main thread.