How to retry an async function with a delay in javascript?

Question

I am trying to fetch a record from a database. Due to race conditions it is possible and even likely that the record isn't there when I first try to fetch it. How do I wrap this in a retry logic without going mad? I seem to be too stupid for it

  const booking = await strapi.query("api::booking.booking").findOne({
    where: {
      id: id,
    },
  });

This code should retry n times with a delay of t milliseconds. Thanks and much love.

What I've tried:

async function tryFetchBooking(
  id,
  max_retries = 3,
  current_try = 0,
  promise
) {
  promise = promise || new Promise();

  // try doing the important thing
  const booking = await strapi.query("api::booking.booking").findOne({
    where: {
      id: id,
    },
  });

  if (!booking) {
    if (current_try < max_retries) {
      console.log("No booking. Retrying");
      setTimeout(function () {
        tryFetchBooking(id, max_retries, current_try + 1, promise);
      }, 500);
    } else {
      console.log("No booking. Giving up.");
      promise.reject(new Error("no booking found in time"));
    }
    promise.catch(() => {
      throw new Error(`Failed retrying 3 times`);
    });
  } else {
    console.log("Found booking with retry");
    promise.resolve(booking);
  }
}

const booking = await tryFetchBooking(id);

The thrown error:

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(). The promise rejected with the reason:
TypeError: Promise resolver undefined is not a function

@SergeySosunov could you give me an example how to use it in my case? I'm struggling with the phrase "This is how you call it, assuming that func sometimes succeeds and sometimes fails, always returning a string that we can log:" So how does my function of fetching a booking would fail? It either returns a record or nothing. — Ole Spaarmann
– Ole Spaarmann, Commented Jul 21, 2022 at 22:11

Bergi · Accepted Answer · 2022-07-21 22:49:05Z

6

That promise.reject()/promise.resolve() approach is not going to work, you cannot resolve a promise from the outside. And you shouldn't need to - just return/throw from your async function! The only place where you need to construct a new Promise is in a little helper function

function delay(t) {
  return new Promise(resolve => {
    setTimeout(resolve, t);
  });
}

Then you can write your function in a recursive manner:

async function tryFetchBooking(
  id,
  max_retries = 3,
  current_try = 0,
) {
  let booking = await strapi.query("api::booking.booking").findOne({
    where: {
      id: id,
    },
  });

  if (!booking) {
    if (current_try < max_retries) {
      console.log("No booking. Retrying");
      await delay(500);
//    ^^^^^^^^^^^^^^^^
      booking = await tryFetchBooking(id, max_retries, current_try + 1);
//              ^^^^^^^^^^^^^^^^^^^^^
      console.log("Found booking with retry");
    } else {
      console.log("No booking. Giving up.");
      throw new Error("no booking found in time");
      // or if you prefer the other error message:
      throw new Error(`Failed retrying 3 times`);
    }
  }
  return booking;
}

or even in an iterative manner:

async function tryFetchBooking(id, maxRetries = 3) {
  let currentTry = 0;
  while (true) {
    const booking = await strapi.query("api::booking.booking").findOne({
      where: {
        id: id,
      },
    });

    if (booking) {
      return booking;
    }
    if (currentTry < maxRetries) {
      await delay(500);
      currentTry++;
    } else {
      console.log("No booking. Giving up.");
      throw new Error("no booking found in time");
    }
  }
}

edited Jul 21, 2022 at 22:49

answered Jul 21, 2022 at 22:41

Bergi

671k162 gold badges1k silver badges1.5k bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Ole Spaarmann Over a year ago

That worked. Thanks! Only issue with your first solution was an thrown error because of re-assignment to a constant variable (booking). But that was an easy fix.

Giang · Accepted Answer · 2023-03-13 08:32:47Z

1

to avoid using await inside a loop, you can use recursive function to call tryFetchBooking

async function tryFetchBooking(id, currentRetry = 0) {
  const maxRetries = 3;
  const booking = await strapi.query("api::booking.booking").findOne({
    where: {
      id: id,
    },
  });
  if (booking) {
    return booking;
  }
  if (currentRetry < maxRetries) {
    await delay(500);
    currentTry++;
    return tryFetchBooking(id, currentRety);
  } else {
    console.log("No booking. Giving up.");
    throw new Error("no booking found in time");
  }
}

answered Mar 13, 2023 at 8:32

Giang

2,8392 gold badges29 silver badges28 bronze badges

Comments

Sergey Sosunov · Accepted Answer · 2022-07-21 23:03:44Z

0

import { strapiMock } from "./mock";

const wait = (ms) => new Promise((r) => setTimeout(r, ms));

// Credits to @Bergi
const retryOperation = (operation, delay, retries) =>
  operation().catch((reason) =>
    retries > 0
      ? wait(delay).then(() => retryOperation(operation, delay, retries - 1))
      : Promise.reject(reason)
  );

const throwIfNoResult = (result) => {
  if (!result) throw new Error("No result");
  return result;
};

const fetchBooking = (id) => {
  /*
  return strapi.query("api::booking.booking").findOne({
    where: {
      id: id
    }
  });
  */
  return strapiMock(id);
};

async function tryFetchBooking(id, delay = 1000, retries = 4) {
  const operation = () => fetchBooking(id).then(throwIfNoResult);
  const wrapped = retryOperation(operation, delay, retries);
  return await wrapped;
}

tryFetchBooking(1).then(console.log).catch(console.error);

Mock used:

let cnt = 0;

export const strapiMock = (id) => {
  return new Promise((resolve, reject) => {
    if (cnt++ === 3) {
      cnt = 0;
      // resolve(null);
      resolve(id);
    } else {
      reject("no data");
    }
  });
};

edited Jul 21, 2022 at 23:03

answered Jul 21, 2022 at 22:22

Sergey Sosunov

4,6502 gold badges13 silver badges21 bronze badges

4 Comments

Bergi Over a year ago

Avoid the Promise constructor antipattern!

Sergey Sosunov Over a year ago

@Bergi please, if you can and have time, can you explain what undesirable consequences can my code lead to? I tried to choose the most convenient approach in terms of reuse, your answer is obviously better, but if I have to do 10-20 methods in the same way - I'll get a little upset

Bergi Over a year ago

It's simply much more complicated, and much harder to get the error handling right (although you did achieve that afaics). So simplify to

const retryOperation = (operation, delay, retries) => operation().catch(reason => retries > 0 ? wait(delay).then(() => retryOperation(operation, delay, retries-1)) : Promise.reject(reason));

Sergey Sosunov Over a year ago

@Bergi Thank you, much better now

Collectives™ on Stack Overflow

How to retry an async function with a delay in javascript?

3 Answers 3

1 Comment

Comments

4 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

1 Comment

Comments

4 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related