parallel-buffered-runner.js

/**
 * A test Runner that uses a {@link module:buffered-worker-pool}.
 * @module parallel-buffered-runner
 * @private
 */

'use strict';

const allSettled = require('promise.allsettled');
const Runner = require('../runner');
const {EVENT_RUN_BEGIN, EVENT_RUN_END} = Runner.constants;
const debug = require('debug')('mocha:parallel:parallel-buffered-runner');
const {BufferedWorkerPool} = require('./buffered-worker-pool');
const {setInterval, clearInterval} = global;
const {createMap} = require('../utils');

/**
 * Outputs a debug statement with worker stats
 * @param {BufferedWorkerPool} pool - Worker pool
 */
/* istanbul ignore next */
const debugStats = pool => {
  const {totalWorkers, busyWorkers, idleWorkers, pendingTasks} = pool.stats();
  debug(
    '%d/%d busy workers; %d idle; %d tasks queued',
    busyWorkers,
    totalWorkers,
    idleWorkers,
    pendingTasks
  );
};

/**
 * The interval at which we will display stats for worker processes in debug mode
 */
const DEBUG_STATS_INTERVAL = 5000;

const ABORTED = 'ABORTED';
const IDLE = 'IDLE';
const ABORTING = 'ABORTING';
const RUNNING = 'RUNNING';
const BAILING = 'BAILING';
const BAILED = 'BAILED';
const COMPLETE = 'COMPLETE';

const states = createMap({
  [IDLE]: new Set([RUNNING, ABORTING]),
  [RUNNING]: new Set([COMPLETE, BAILING, ABORTING]),
  [COMPLETE]: new Set(),
  [ABORTED]: new Set(),
  [ABORTING]: new Set([ABORTED]),
  [BAILING]: new Set([BAILED, ABORTING]),
  [BAILED]: new Set([COMPLETE, ABORTING])
});

/**
 * This `Runner` delegates tests runs to worker threads.  Does not execute any
 * {@link Runnable}s by itself!
 * @private
 */
class ParallelBufferedRunner extends Runner {
  constructor(...args) {
    super(...args);

    let state = IDLE;
    Object.defineProperty(this, '_state', {
      get() {
        return state;
      },
      set(newState) {
        if (states[state].has(newState)) {
          state = newState;
        } else {
          throw new Error(`invalid state transition: ${state} => ${newState}`);
        }
      }
    });

    this.once(Runner.constants.EVENT_RUN_END, () => {
      this._state = COMPLETE;
    });
  }

  /**
   * Returns a mapping function to enqueue a file in the worker pool and return results of its execution.
   * @param {BufferedWorkerPool} pool - Worker pool
   * @param {Options} options - Mocha options
   * @returns {FileRunner} Mapping function
   */
  _createFileRunner(pool, options) {
    return async file => {
      debug('run(): enqueueing test file %s', file);
      try {
        const {failureCount, events} = await pool.run(file, options);
        if (this._state === BAILED) {
          // short-circuit after a graceful bail. if this happens,
          // some other worker has bailed.
          // TODO: determine if this is the desired behavior, or if we
          // should report the events of this run anyway.
          return;
        }
        debug(
          'run(): completed run of file %s; %d failures / %d events',
          file,
          failureCount,
          events.length
        );
        this.failures += failureCount; // can this ever be non-numeric?
        let event = events.shift();
        while (event) {
          this.emit(event.eventName, event.data, event.error);
          if (
            this._state !== BAILING &&
            event.data &&
            event.data._bail &&
            (failureCount || event.error)
          ) {
            debug('run(): nonzero failure count & found bail flag');
            // we need to let the events complete for this file, as the worker
            // should run any cleanup hooks
            this._state = BAILING;
          }
          event = events.shift();
        }
        if (this._state === BAILING) {
          debug('run(): terminating pool due to "bail" flag');
          this._state = BAILED;
          await pool.terminate();
        }
      } catch (err) {
        if (this._state === BAILED || this._state === ABORTING) {
          debug(
            'run(): worker pool terminated with intent; skipping file %s',
            file
          );
        } else {
          // this is an uncaught exception
          debug('run(): encountered uncaught exception: %O', err);
          if (this.allowUncaught) {
            // still have to clean up
            this._state = ABORTING;
            await pool.terminate(true);
          }
          throw err;
        }
      } finally {
        debug('run(): done running file %s', file);
      }
    };
  }

  /**
   * Listen on `Process.SIGINT`; terminate pool if caught.
   * Returns the listener for later call to `process.removeListener()`.
   * @param {BufferedWorkerPool} pool - Worker pool
   * @returns {SigIntListener} Listener
   */
  _bindSigIntListener(pool) {
    const sigIntListener = async () => {
      debug('run(): caught a SIGINT');
      this._state = ABORTING;

      try {
        debug('run(): force-terminating worker pool');
        await pool.terminate(true);
      } catch (err) {
        console.error(
          `Error while attempting to force-terminate worker pool: ${err}`
        );
        process.exitCode = 1;
      } finally {
        process.nextTick(() => {
          debug('run(): imminent death');
          this._state = ABORTED;
          process.kill(process.pid, 'SIGINT');
        });
      }
    };

    process.once('SIGINT', sigIntListener);

    return sigIntListener;
  }

  /**
   * Runs Mocha tests by creating a thread pool, then delegating work to the
   * worker threads.
   *
   * Each worker receives one file, and as workers become available, they take a
   * file from the queue and run it. The worker thread execution is treated like
   * an RPC--it returns a `Promise` containing serialized information about the
   * run.  The information is processed as it's received, and emitted to a
   * {@link Reporter}, which is likely listening for these events.
   *
   * @param {Function} callback - Called with an exit code corresponding to
   * number of test failures.
   * @param {{files: string[], options: Options}} opts - Files to run and
   * command-line options, respectively.
   */
  run(callback, {files, options} = {}) {
    /**
     * Listener on `Process.SIGINT` which tries to cleanly terminate the worker pool.
     */
    let sigIntListener;
    // This function should _not_ return a `Promise`; its parent (`Runner#run`)
    // returns this instance, so this should do the same. However, we want to make
    // use of `async`/`await`, so we use this IIFE.

    (async () => {
      /**
       * This is an interval that outputs stats about the worker pool every so often
       */
      let debugInterval;

      /**
       * @type {BufferedWorkerPool}
       */
      let pool;

      try {
        pool = BufferedWorkerPool.create({maxWorkers: options.jobs});

        sigIntListener = this._bindSigIntListener(pool);

        /* istanbul ignore next */
        debugInterval = setInterval(
          () => debugStats(pool),
          DEBUG_STATS_INTERVAL
        ).unref();

        // this is set for uncaught exception handling in `Runner#uncaught`
        // TODO: `Runner` should be using a state machine instead.
        this.started = true;
        this._state = RUNNING;

        this.emit(EVENT_RUN_BEGIN);

        const results = await allSettled(
          files.map(this._createFileRunner(pool, options))
        );

        // note that pool may already be terminated due to --bail
        await pool.terminate();

        results
          .filter(({status}) => status === 'rejected')
          .forEach(({reason}) => {
            if (this.allowUncaught) {
              // yep, just the first one.
              throw reason;
            }
            // "rejected" will correspond to uncaught exceptions.
            // unlike the serial runner, the parallel runner can always recover.
            this.uncaught(reason);
          });

        if (this._state === ABORTING) {
          return;
        }
        this.emit(EVENT_RUN_END);
        debug('run(): completing with failure count %d', this.failures);
        callback(this.failures);
      } catch (err) {
        // this `nextTick` takes us out of the `Promise` scope, so the
        // exception will not be caught and returned as a rejected `Promise`,
        // which would lead to an `unhandledRejection` event.
        process.nextTick(() => {
          debug('run(): re-throwing uncaught exception');
          throw err;
        });
      } finally {
        clearInterval(debugInterval);
        process.removeListener('SIGINT', sigIntListener);
      }
    })();
    return this;
  }
}

module.exports = ParallelBufferedRunner;

/**
 * Listener function intended to be bound to `Process.SIGINT` event
 * @private
 * @callback SigIntListener
 * @returns {Promise<void>}
 */

/**
 * A function accepting a test file path and returning the results of a test run
 * @private
 * @callback FileRunner
 * @param {string} filename - File to run
 * @returns {Promise<SerializedWorkerResult>}
 */