BUG_UnhandledPromiseRejectionWarning: DataCloneError: eventName

Describe the bug A clear and concise description of what the bug is. I tried to create Fixed and Dynamic ThreadPools as follows and try to pass the mongo db instance to the worker. It throws an error as follows:

api      |     Merkle Root: 0x29711e9454dc2c1d629c0cdc0b0924d762db96cd86b3702c4af32b71469e2fa8
api      | (node:21) UnhandledPromiseRejectionWarning: DataCloneError: eventName => {
api      |     if (DEPRECATED_UNIFIED_EVENTS.has(eventName)) {
api      |       emitDeprecationWarning(
api      |         `The \...<omitted>... } could not be cloned.
api      |     at Worker.postMessage (internal/worker.js:223:23)
api      |     at g.sendToWorker (/usr/api/node_modules/poolifier/lib/index.js:1:5850)
api      |     at g.execute (/usr/api/node_modules/poolifier/lib/index.js:1:3871)
api      |     at sendCredentialIssuedEmail (/usr/api/src/email/sendCredentialIssuedEmail.js:85:14)
api      |     at Server.issueAndPublishCertificates (/usr/api/src/routes/issuer.js:282:5)
api      |     at processTicksAndRejections (internal/process/task_queues.js:93:5)
api      | (node:21) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). (rejection id: 1)
api      | (node:21) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.

Using Cluster Fixed Pool gave following issue :

api      |     Merkle Root: 0x211155733b5f5bd5e88f99c833fb0c95917aa6fd7d4bb51cb5e2b443acb05590
api      | (node:19) UnhandledPromiseRejectionWarning: TypeError: Converting circular structure to JSON
api      |     --> starting at object with constructor 'NativeTopology'
api      |     |     property 's' -> object with constructor 'Object'
api      |     |     property 'sessionPool' -> object with constructor 'ServerSessionPool'
api      |     --- property 'topology' closes the circle
api      |     at JSON.stringify (<anonymous>)
api      |     at ChildProcess.target._send (internal/child_process.js:778:25)
api      |     at ChildProcess.target.send (internal/child_process.js:676:19)
api      |     at Worker.send (internal/cluster/worker.js:43:28)
api      |     at y.sendToWorker (/usr/api/node_modules/poolifier/lib/index.js:1:5413)
api      |     at y.execute (/usr/api/node_modules/poolifier/lib/index.js:1:3871)
api      |     at sendCredentialIssuedEmail (/usr/api/src/email/sendCredentialIssuedEmail.js:85:14)
api      |     at Server.issueAndPublishCertificates (/usr/api/src/routes/issuer.js:282:5)
api      |     at processTicksAndRejections (internal/process/task_queues.js:93:5)
api      | (node:19) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). (rejection id: 1)
api      | (node:19) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.

Steps to reproduce the behavior

    const workerScript = path.join(__dirname, './yourWorker.js');
    const pool = new FixedThreadPool(15,
        workerScript,
        { errorHandler: (e) => console.error(e), onlineHandler: () => console.log('worker is online') })

    let resolved = 0
    const start = Date.now()
    const certsCount = _.size(issuedCerts);
    for (const issuedCert of issuedCerts) {
        pool
            .execute({
                cert: issuedCert,
                db,
            })
            .then(res => {
                resolved++
                if (resolved === certsCount) {
                    return console.log('Time take is ' + (Date.now() - start))
                }
                return null
            })
            .catch(err => console.error(err));
    }

Info

Tool	Version
Poolifier	v2.0.1
Node	v node:12.13.1-stretch - Docker
OS	linux - Debian - Docker

Additional context

Worker is an async task processor Tried both Fixed and Dynamic Pools

[pioardi]

Hi @chamikabm nice to meet you and thanks to use poolifier. As per node.js documentation you can only pass serializable data from the main process to the worker threads. I think this is the main issue here, you could try to have one mongodb client instance per thread ,but my suggestion is to avoid I/O operations ( like write/read from a database ) into worker threads since they are particurlarlly useful for CPU tasks. You can try to split your tasks in two/three and only do CPU stuff in worker threads, or in alternative try to instantiate the mongodb client into the worker thread directly.

Hope this helps

[chamikabm]

@pioardi Yes, it is resolved. Thanks for being helpful! And for this awesome library. Looking forward to seeing more features. Cheers!