Queuing function using RxJS

问题

I'm using rxjs with NodeJS in backend. I have a Rest API which allow consumers to run remote yarn installation process. The install function returns an observable of the process. So when the module is installed successfully it emits a value in the observable and complete. At this point, the Rest API will returns a response to the user to say that the installation is successful. In case that the installation fails, the process will throw an Error in the stream and the Rest API returns another response with the error information.

My issue is:

The API is called multiple times in parallel by consumers, so there will be a parallel installations in the backend.

I tried throttle operator to create a queue but it keeps the first stream active. So if the first process is "completed", it returns "true" but the stream doesn't complete

export class MyService {
    // the function called by the REST API
    installGlobal(moduleName: string): Observable < boolean > {
        // I think, there are something to do here to make it queuing
        return this.run('yarn', ['global', 'add', moduleName]);
    }

    private run(cmd: string, args: string[]): Observable < boolean > {
        const cmd$ = fromPromise(spawn(cmd, args)).pipe(
            map(stdout => {
                this.logger.info(`Install Module Successfully`);
                this.logger.info(`stdout: ${stdout.toString()}`);
                return true;
            }),
            catchError(error => {
                const errorMessage: string = error.stderr.toString();
                return _throw(errorMessage.substr(errorMessage.indexOf(' ') + 1));
            })
        );
        return cmd$;
    }
}

My expectation:

Either there are multiple request, they must be queued. So the first one will be treated and all parallel onces must be queued. When the first is processed, it must returns the response to the API consumers (like 200 completed) and resume the next stream from the queue.

[UPDATE-01 July 2019]: adding an example

You can fetch a demo of the code at stackblitz

I have reimplemented the existant code and i'm simulating my API call by subscribing multi time to the service which will call the queue

回答1:

A simple queque in Rxjs can be done like below

const queque=new Subject()
// sequential processing
queue.pipe(concatMap(item=>yourObservableFunction(item)).subscribe()
// add stuff to the queue 
queque.next(item)

来源：https://stackoverflow.com/questions/56740884/queuing-function-using-rxjs

标签

rxjs

rxjs-pipeable-operators