core-redux-saga

name	core/redux-saga
description	Generic redux-saga API reference for agents. Covers createSagaMiddleware, middleware.run, runSaga, Effect creators, effect combinators, watcher helpers, channel support, buffers, Task/Channel/Buffer/SagaMonitor interfaces, cancellation, context, blocking vs non-blocking semantics, and testing helpers.
type	core
sources	["https://redux-saga.js.org/docs/api"]
triggers	["redux-saga","redux saga API","createSagaMiddleware","saga effects","saga channels","runSaga","saga cancellation","saga testing"]

redux-saga — API reference skill

Source: official redux-saga API Reference, https://redux-saga.js.org/docs/api, retrieved 2026-05-15.

Use this skill for generic redux-saga API behavior. When editing this repository'sthemis code, also follow the package-specific core saga skills in sibling ../* skill folders, especially the typed-redux-saga yield*conventions and canonical watcher ownership rules.

Agent Preflight Compliance Contract

Before editing code or docs that use this skill:

• MUST identify whether the target code uses plain redux-saga or this repo'styped-redux-saga conventions; adapt examples accordingly.
• MUST cite this skill and any package-specific saga skill used in the handoff.
• MUST verify watcher ownership before adding takeEvery, takeLatest,takeLeading, throttle, or debounce for an existing trigger.
• SHOULD prefer native redux-saga channel-aware effects before adding wrapperutilities.
• MUST NOT introduce detached spawn in this repository; use attached fork so parent failure/cancellation also reaches children.
• MUST implement repository debounce with takeLatest or takeLeading plus delay, not action-wrapper debounce utilities.
• NEVER introduce runtime source, dependency, or artifact routing changes whenonly API guidance is requested.

Setup — middleware and root saga startup

createSagaMiddleware(options) creates Redux middleware. Supported options includeinitial context, sagaMonitor, onError, effectMiddlewares, and a customchannel used by take and put effects.

In themis app setup, the concrete Store owns saga middleware creation. Use this low-level API reference to understand redux-saga behavior, but configure Store-owned monitoring by passing { sagaMonitor: true } in the third Store/ReactStore/StreamingStore constructor options argument instead of replacing the middleware. Omitted or false saga monitoring remains disabled.

import { applyMiddleware, createStore } from "redux";
import createSagaMiddleware from "redux-saga";
import { all, call } from "redux-saga/effects";

function reducer(state = { ready: false }, action: { type: string }) {
  return action.type === "READY" ? { ready: true } : state;
}

function* rootSaga() {
  yield all([call(backgroundSync)]);
}

const sagaMiddleware = createSagaMiddleware({
  onError(error, { sagaStack }) {
    console.error("uncaught saga error", error, sagaStack);
  },
});

const store = createStore(reducer, applyMiddleware(sagaMiddleware));
const task = sagaMiddleware.run(rootSaga);

function* backgroundSync() {
  yield call(Promise.resolve, undefined);
}

void task.toPromise();

middleware.run(saga, ...args) must be called after the saga middleware is mountedon the store. It returns a Task descriptor and drives yielded plain Effectobjects until the generator returns, throws, or is cancelled.

Core patterns

1. Waiting and watcher helpers

Use take(pattern) for one action, takeMaybe(pattern) when the saga must receivethe END sentinel instead of auto-terminating, and watcher helpers for commonloops. Patterns can be "*", strings, arrays, predicates, or action creators whosetoString() returns an action type.

import { call, fork, put, take, takeEvery, takeLatest, takeLeading } from "redux-saga/effects";

function* loadUser(action: { type: string; userId: string }) {
  const user: User = yield call(api.loadUser, action.userId);
  yield put({ type: "USER_LOADED", user });
}

export function* usersSaga() {
  yield takeEvery("USER_REQUESTED", loadUser);     // concurrent workers
  yield takeLatest("SEARCH_CHANGED", runSearch);   // cancel stale worker
  yield takeLeading("SUBMIT_ORDER", submitOrder);  // ignore while running

  const action: { type: string } = yield take(["LOGOUT", "SESSION_EXPIRED"]);
  yield fork(cleanupSession, action);
}

takeEvery, takeLatest, takeLeading, throttle, and debounce also accept aChannel in place of a pattern. This is native redux-saga behavior; do not createwrapper utilities unless they add cleanup, typing, or domain value beyond the API.

2. Blocking and non-blocking effects

call, apply, and cps are blocking; fork and spawn start work without blocking the parent. fork is attached to the parent: parent completion waits for children, child errors bubble upward, and cancellation propagates downward. spawn is detached and does not share parent completion, error, or cancellation flow. In this repository, agents must use attached fork, not detached spawn, so child tasks remain cancellable and failures remain visible to the parent lifecycle.

import { call, cancel, cancelled, fork, join } from "redux-saga/effects";

function* worker() {
  try {
    yield call(api.sync);
  } finally {
    if (yield cancelled()) yield call(api.abortSync);
  }
}

function* supervisor() {
  const attachedTask: Task = yield fork(worker);
  const metricsTask: Task = yield fork(backgroundMetrics);
  yield cancel(metricsTask);  // non-blocking cancellation request
  yield join(attachedTask);   // blocking wait for attachedTask outcome
}

Use cancel(task), cancel([...tasks]), or cancel() for self-cancellation.Cancellation calls the generator's return(), jumps to finally, and cancels thecurrently blocked effect plus attached child tasks.

3. Store I/O, state reads, context, and timing

Use put(action) for scheduled dispatch, putResolve(action) when dispatch returnsa Promise and the saga must wait, put(channel, message) for channel output, andselect(selector, ...args) for state reads. setContext(props) merges saga context;getContext(prop) reads one context value. delay(ms, value) blocks for time.

import { call, delay, getContext, put, putResolve, retry, select, setContext } from "redux-saga/effects";

function* saveProfile(action: { type: string; id: string }) {
  const token: string = yield select((state: RootState) => state.session.token);
  yield setContext({ requestId: action.id });
  const requestId: string = yield getContext("requestId");

  const profile: Profile = yield retry(3, 1_000, api.loadProfile, token, requestId);
  yield put({ type: "PROFILE_LOADED", profile });
  yield delay(250);
  yield putResolve({ type: "PROFILE_PERSISTED" });
}

retry(maxTries, delayMs, fn, ...args) is a blocking helper built from call anddelay: it retries failures until success or attempts are exhausted, then rethrowsthe last error.

4. Channels, buffers, and cleanup

Use actionChannel(pattern, buffer?) to queue matching store actions while a workeris blocked. Use channel(buffer?) for task-to-task messages and eventChannel tobridge external event sources; the subscribe function must return an unsubscribefunction. Close channels in finally, and use flush(channel) to recover bufferedmessages during cleanup.

import { buffers, channel, eventChannel, END } from "redux-saga";
import { actionChannel, call, flush, put, take } from "redux-saga/effects";

function socketChannel(socket: WebSocket) {
  return eventChannel<string>((emit) => {
    socket.onmessage = (event) => emit(String(event.data));
    socket.onerror = () => emit(END);
    return () => socket.close();
  }, buffers.sliding(10));
}

function* serializeRequests() {
  const requests: Channel<RequestAction> = yield actionChannel("REQUEST", buffers.expanding(10));
  try {
    while (true) {
      const action: RequestAction = yield take(requests);
      yield call(api.sendRequest, action.payload);
    }
  } finally {
    const leftovers: RequestAction[] = yield flush(requests);
    yield put({ type: "REQUESTS_FLUSHED", leftovers });
  }
}

const mailbox = channel<string>(buffers.fixed(5));

Buffer choices: buffers.none(), fixed(limit), expanding(initialSize),dropping(limit), and sliding(limit). The default channel() buffer queues upto 10 messages FIFO.

5. Concurrency combinators and helpers

Use race when the first completion wins; losing effects are automaticallycancelled. Use all to run effects in parallel and wait for all successes, or throwwhen any effect rejects.

import { all, call, delay, put, race, take, takeLatest, takeLeading, throttle } from "redux-saga/effects";

function* fetchWithTimeout() {
  const { response, timeout } = yield race({
    response: call(api.fetchReport),
    timeout: delay(5_000),
  });
  if (timeout) yield put({ type: "REPORT_TIMEOUT" });
  else yield put({ type: "REPORT_READY", response });
}

function* refreshResultsAfterSettled(action: { type: string; query: string }) {
  yield delay(300);
  yield call(refreshResults, action.query);
}

function* refreshOncePerWindow(action: { type: string; id: string }) {
  try {
    yield call(refreshPanel, action.id);
  } finally {
    yield delay(300);
  }
}

function* rootSaga() {
  yield all([call(fetchWithTimeout), call(watchUpload)]);
  yield throttle(1_000, "TYPEAHEAD_CHANGED", fetchSuggestions);
  yield takeLatest("FILTER_CHANGED", refreshResultsAfterSettled);
  yield takeLeading("REFRESH_CLICKED", refreshOncePerWindow);
  yield take("SHUTDOWN");
}

throttle(ms, patternOrChannel, saga, ...args) uses a sliding buffer of one recentmessage while suppressing new starts during the window. Upstream redux-saga also exposes a native debounce(ms, patternOrChannel, saga, ...args) helper that waits until messages settle before forking the worker, but agents must not use it for themis implementation examples. Repository debounce must be written explicitly with takeLatest or takeLeading plus delay so cancellation semantics are visible in the worker.

Interface quick reference

Interface	What agents need to know
Task	Returned by fork, spawn, middleware.run, and runSaga; supports isRunning(), isCancelled(), result(), error(), toPromise(), and cancel().
Channel	Message queue with take(callback), put(message), flush(callback), and close(); closed empty channels deliver END.
Buffer	Strategy behind a channel; implements isEmpty(), put(message), and take().
SagaMonitor	Receives rootSagaStarted, effectTriggered, effectResolved, effectRejected, effectCancelled, and actionDispatched events for instrumentation.

Blocking / non-blocking cheat sheet

Effect	Blocking?	Notes
take, takeMaybe, call, apply, cps, join, putResolve, cancelled, delay, retry, race	Yes	race blocks until one branch wins, then cancels losers.
put, fork, spawn, cancel, actionChannel, flush, select, setContext, getContext	No	select resolves immediately against current state.
put(channel, message)	Depends	It can block when an unbuffered put is consumed immediately by a taker.
all([...]) / all({ ... })	Mixed	Blocks until all child effects complete; child effect types determine actual waits.
takeEvery, takeLatest, takeLeading, throttle, debounce	No	Helpers fork watcher tasks; their internals may use blocking effects.

External execution with runSaga

runSaga(options, saga, ...args) starts a saga without Redux middleware. Provide achannel for take, a dispatch(output) function for put, and getState() forselect. It returns the same Task interface as middleware.run.

import { runSaga, stdChannel } from "redux-saga";
import { put, take } from "redux-saga/effects";

function* auditSaga() {
  const action: { type: string } = yield take("AUDIT");
  yield put({ type: "AUDITED", action });
}

const dispatched: Array<{ type: string; action?: { type: string } }> = [];
const input = stdChannel();
const task = runSaga(
  { channel: input, dispatch: (output) => dispatched.push(output), getState: () => ({}) },
  auditSaga,
);

input.put({ type: "AUDIT" });
await task.toPromise();

Testing helpers

• cloneableGenerator(generatorFunc) from @redux-saga/testing-utils createscloneable generator instances for branch testing without replaying setup yields.
• createMockTask() from @redux-saga/testing-utils returns a mock Task fortesting fork, join, and cancel flows.
• Prefer effect-level assertions for small generators and integration-style sagatests for cancellation, channel cleanup, and watcher concurrency.

import { cloneableGenerator, createMockTask } from "@redux-saga/testing-utils";
import { cancel, fork } from "redux-saga/effects";

function* worker() {}
function* parent() {
  const task: Task = yield fork(worker);
  yield cancel(task);
}

const generator = cloneableGenerator(parent)();
expect(generator.next().value).toEqual(fork(worker));
const mockTask = createMockTask();
expect(generator.next(mockTask).value).toEqual(cancel(mockTask));

Common mistakes

❌ Calling middleware.run before mounting middleware

middleware.run is only valid after the saga middleware is connected to the Reduxstore. Mount middleware first, then run the root saga. Source: redux-saga APIReference → middleware.run(saga, ...args). Priority: HIGH.

❌ Assuming take and takeMaybe handle END the same way

take(pattern) and take(channel) auto-terminate when they receive END from thestdChannel or a closed channel. takeMaybe returns the END object so the saga canhandle the closed-input case itself. Source: redux-saga API Reference → take /takeMaybe. Priority: MEDIUM.

❌ Using spawn when parent failure/cancellation must affect the child

fork creates an attached task; errors bubble to the parent and cancellation propagates through attached children. In this repository, do not introduce spawn; use fork so saga-manager and parent lifecycles can observe failures and cancel children. Source: redux-saga API Reference → fork / spawn. Priority: HIGH.

❌ Forgetting channel unsubscribe / close cleanup

eventChannel subscribe functions must return an unsubscribe callback, and sagaconsumers should close channels in finally when they own the channel lifecycle.Source: redux-saga API Reference → eventChannel / Channel. Priority: HIGH.

❌ Recreating native channel helpers as wrappers without added value

takeEvery, takeLatest, takeLeading, throttle, and debounce already acceptchannels. Add wrappers only for documented cleanup, typing, or domain-specificbehavior. Source: redux-saga API Reference → channel overloads for watcher helpers.Priority: MEDIUM.

For this repository's action debouncing, do not add wrapper-action debounce utilities; watch the real action with takeLatest or takeLeading and use delay inside the worker.

See also

• ../sagas/SKILL.md — repository-specific typed-redux-saga conventions.
• ../channel-effects/SKILL.md — package-provided channel consumer wrappers and when they add cleanup value.
• ../testing/SKILL.md — repository-specific saga test patterns and mocks.