feat(worker): resourceLimits for worker isolates - #471
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Included review availability: Your plan provides up to 2 included reviews per hour; 0 remain after this review. 📝 WalkthroughWalkthroughWorkers now accept Node-style resource limits for V8 heap generations and JS dispatch-table reservations. The runtime applies these limits, monitors heap exhaustion, reports errors, terminates affected workers, and tests valid and invalid configurations. ChangesWorker resource limits
Estimated code review effort: 4 (Complex) | ~45 minutes Merge Risk: ⚪ Minimal · up to Workers now support bounded resource limits and report then terminate on heap exhaustion. Validation, startup, and OOM behavior are covered, with no concrete merge-blocking risk identified. Sequence Diagram(s)sequenceDiagram
participant WorkerOptions
participant Worker
participant Runtime
participant WorkerWrapper
participant V8
participant MainRuntime
WorkerOptions->>Worker: Provide resourceLimits
Worker->>Runtime: CreateIsolate(resourceLimits)
Runtime->>V8: Apply heap and dispatch-table limits
Worker->>WorkerWrapper: WatchHeapLimit(isolate)
V8->>WorkerWrapper: Invoke OnNearHeapLimit
WorkerWrapper->>MainRuntime: Report out-of-memory error
WorkerWrapper->>V8: Request termination and raise limit
Worker->>WorkerWrapper: Check HeapLimitExceeded()
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Inline comments:
In `@NativeScript/runtime/Worker.mm`:
- Around line 169-172: Update both heap-limit conversion branches in Worker.mm
(anchor lines 169-172 and sibling lines 174-177) to validate the value returned
by ReadMegabyteLimit before converting: reject finite values whose byte count
exceeds size_t’s representable range or converts to zero, and apply the same
guard to both maxOldGenerationSizeMb and the sibling heap-limit key. Add tests
covering oversized finite inputs for both keys.
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NativeScript/runtime/DataWrapper.hNativeScript/runtime/NativeScriptException.mmNativeScript/runtime/Runtime.hNativeScript/runtime/Runtime.mmNativeScript/runtime/Worker.mmNativeScript/runtime/WorkerWrapper.mmTestRunner/app/tests/WorkerResourceLimitsTests.jsTestRunner/app/tests/index.jsTestRunner/app/tests/workerResourceLimits/echoWorker.jsTestRunner/app/tests/workerResourceLimits/oomWorker.js
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Adds Node's `resourceLimits` worker option, at the top level of the options
object rather than under `ios`:
new Worker("./w.js", {
resourceLimits: {
maxOldGenerationSizeMb: 64,
maxYoungGenerationSizeMb: 8,
jsDispatchTableSizeMb: 64,
},
});
The two heap caps map onto v8::ResourceConstraints and are applied through a
new `IsolateLimits` struct that Runtime::CreateIsolate takes; the struct is
threaded through the worker startup lambda so CreateIsolate itself stays free
of worker policy. Values are validated at construction: a non-object
`resourceLimits` or a non-numeric key throws a TypeError, a non-finite or
non-positive value throws a RangeError, and unknown keys are ignored.
`jsDispatchTableSizeMb` is a NativeScript extension compiled behind
V8_HAS_JS_DISPATCH_TABLE_RESERVATION_PARAM. Until the prebuilt V8 carries the
reservation parameter, passing it throws; once it does, worker isolates default
to a 64 MB reservation instead of V8's 256 MB, and the main isolate keeps the
default.
Capping a worker's heap is only useful if exhausting it is recoverable, so
every worker isolate now registers a near-heap-limit callback (Node does the
same unconditionally for workers). It forwards "Worker JS heap out of memory"
to the parent's worker.onerror as a plain string payload, asks V8 to terminate
the isolate and returns the limit raised by 16 MB so the in-progress GC can
finish. Termination goes to the isolate the callback belongs to rather than
through Terminate() alone, because Terminate() only reaches an isolate
BackgroundLooper has already published — which happens after the entry script
finishes evaluating, and a worker that exhausts its heap usually does so inside
that entry.
Building the exception detail for a terminating isolate crashed on the empty
v8::Message such an isolate reports, so GetFullMessage now returns the plain JS
message when there is none, and reads the line number with FromMaybe.
…reservation parameter Enables the jsDispatchTableSizeMb path and the 64 MB worker default that were compiled behind V8_HAS_JS_DISPATCH_TABLE_RESERVATION_PARAM.
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Stacked on #470 — review/merge that one first; this branch targets
feat/worker-ios-options.Option surface
Adds Node's
resourceLimitsworker option, at the top level of the options object (not underios, since the two heap caps are portable):maxOldGenerationSizeMbandmaxYoungGenerationSizeMbkeep Node's names, units and semantics, fractional megabytes included. Node'scodeRangeSizeMbandstackSizeMbhave no equivalent here and are ignored rather than rejected, so code written against Node keeps working.The caps travel as a new
tns::IsolateLimitsstruct thatRuntime::CreateIsolatetakes (defaulted, so the main isolate's call site is unchanged) and that the worker startup lambda captures.CreateIsolateonly applies what it is given — the worker-specific policy stays inWorker.mm.Validation
All of it happens in the
Workerconstructor, on the calling thread, before any worker starts. Every error carries a realTypeError/RangeError/Errorinstance, soinstanceofholds in JS.resourceLimitsabsent,undefinedornullresourceLimitsany other non-objectTypeError, names"resourceLimits"undefined"64",{}, …)TypeError, names the keyNaN,Infinity,0or a negative numberRangeError, names the keyjsDispatchTableSizeMbnot a whole number, or outside[1, 256]RangeError, names the keyMegabytes become bytes as
size_t(mb * 1024 * 1024).Out-of-memory behavior
A heap cap is only useful if reaching it is recoverable — otherwise a capped worker takes the whole process down with V8's fatal OOM. So every worker isolate now registers a near-heap-limit callback, capped or not (Node does the same unconditionally for workers).
When the worker's heap reaches its limit, the callback — which runs on the worker thread from inside a GC, where no JS may run and no handle may be created:
Worker JS heap out of memory (maxOldGenerationSizeMb: N)to the parent'sworker.onerrorthrough the string overload ofPassUncaughtExceptionFromWorkerToMain, which only copies strings onto the parent's event loop and never touches the worker's isolate;Later invocations return the same raised limit and do nothing else (returning a lower limit is fatal to V8). The worker thread then unwinds normally: the running JS terminates, the startup lambda stops before it would run anything else on the terminating isolate, and the looper deletes the
Runtime. This mirrors Node'sERR_WORKER_OUT_OF_MEMORY, which surfaces on the parent's'error'event and leaves the process alive.Termination is requested on the isolate the callback belongs to, not only through
WorkerWrapper::Terminate():Terminate()reachesworkerIsolate_, whichBackgroundLooperpublishes only after the entry script has finished evaluating — and a worker that exhausts its heap usually does so inside that entry.One pre-existing crash surfaced while building this: a terminating isolate reports an exception with an empty
v8::Message, andNativeScriptException::GetFullMessagedereferenced it unconditionally. It now returns the plain JS message when there is none, and reads the line number withFromMaybeinstead ofToChecked.JS dispatch table
jsDispatchTableSizeMbcaps the address space an isolate reserves for its JS dispatch table. It is compiled behindV8_HAS_JS_DISPATCH_TABLE_RESERVATION_PARAM, the macro the V8 patch in v8-buildscripts PR NativeScript/v8-buildscripts#7 defines alongsideIsolate::CreateParams::js_dispatch_table_reservation_size. This PR bumpsV8_RELEASEtov8-14.9.207.39-7, the first prebuilt that carries it; the code still builds against older prebuilts, where the option is rejected as unsupported.v8-buildscripts PR: NativeScript/v8-buildscripts#7
With that prebuilt, worker isolates default to a 64 MB reservation while the main isolate keeps V8's default. iOS budgets a process's address space by device RAM, every isolate otherwise reserves 256 MB for this table, and 64 MB still holds four million dispatch entries — far more than a worker allocates. Apps that need more can raise it per worker.
Verification
TestRunner suite, Debug, iOS Simulator.
feat/worker-ios-options)17 new specs in
WorkerResourceLimitsTests.js: the OOM path end-to-end (a worker capped at 32 MB that allocates without releasing reports throughworker.onerrorand the runner survives), both heap caps applied individually and together,resourceLimits: null, unknown keys, nine validation cases (including a value too large to hold in bytes, one below a byte, and a throwing getter), and workers starting under 64 MB and 1 MB dispatch table reservations. Every other worker spec in the suite now runs under the 64 MB worker default.Follow-ups
WorkerOptions.resourceLimits.resourceLimitsand the near-heap-limit reporting.Summary by CodeRabbit
New Features
Bug Fixes
Tests