Execute many promises sequentially (Concept)
(My target is clarify my concept about the problem, not code)
I want execute a array of promises sequentially, but nodeJS throw a strange error about many promises executed in parallel.(Because i limited that array to 20 promises and works, 50 promises and works, but 9000 promises and explode..)
- I know that we have some solutions like, array.reduce(), loops, etc
- I know about the promises states (my array have pending promises initially)
My question: I can execute 20 promises, then another 20 promises, etc but... If im executing my promises sequentially, nodeJS must execute 9k promises without problem? I have a bad concept? My code is wrong?
(Im doubting because nodeJS wait some time before begin to resolve the promises)
My case: i trying download 9k+ images (with axios), then save each one and then wait 5 seconds sequentially.
[download 1 image, save that image, wait 5 seconds, then download next image, save.., wait..., etc.. ] Possible?
javascript node.js asynchronous promise axios
|
show 10 more comments
(My target is clarify my concept about the problem, not code)
I want execute a array of promises sequentially, but nodeJS throw a strange error about many promises executed in parallel.(Because i limited that array to 20 promises and works, 50 promises and works, but 9000 promises and explode..)
- I know that we have some solutions like, array.reduce(), loops, etc
- I know about the promises states (my array have pending promises initially)
My question: I can execute 20 promises, then another 20 promises, etc but... If im executing my promises sequentially, nodeJS must execute 9k promises without problem? I have a bad concept? My code is wrong?
(Im doubting because nodeJS wait some time before begin to resolve the promises)
My case: i trying download 9k+ images (with axios), then save each one and then wait 5 seconds sequentially.
[download 1 image, save that image, wait 5 seconds, then download next image, save.., wait..., etc.. ] Possible?
javascript node.js asynchronous promise axios
2
So first question, why in the world would you want to chain 9000 promises? That is just poor design. Doesn't the api or tool you use offer bulk gets?
– basic
Jan 3 at 14:45
i cannot find any reasons for such an amount of promises
– messerbill
Jan 3 at 14:49
If we talk theoretically, did you try to config node to run with more memory?
– Maayao
Jan 3 at 14:51
1
I think Promise.all only care about if all promises was resolved, and allow execute in parallel, i tried it. Thanks
– AndresSp
Jan 3 at 15:00
1
Take a look at this npm package: npmjs.com/package/promise-queue
– Jaime
Jan 3 at 15:24
|
show 10 more comments
(My target is clarify my concept about the problem, not code)
I want execute a array of promises sequentially, but nodeJS throw a strange error about many promises executed in parallel.(Because i limited that array to 20 promises and works, 50 promises and works, but 9000 promises and explode..)
- I know that we have some solutions like, array.reduce(), loops, etc
- I know about the promises states (my array have pending promises initially)
My question: I can execute 20 promises, then another 20 promises, etc but... If im executing my promises sequentially, nodeJS must execute 9k promises without problem? I have a bad concept? My code is wrong?
(Im doubting because nodeJS wait some time before begin to resolve the promises)
My case: i trying download 9k+ images (with axios), then save each one and then wait 5 seconds sequentially.
[download 1 image, save that image, wait 5 seconds, then download next image, save.., wait..., etc.. ] Possible?
javascript node.js asynchronous promise axios
(My target is clarify my concept about the problem, not code)
I want execute a array of promises sequentially, but nodeJS throw a strange error about many promises executed in parallel.(Because i limited that array to 20 promises and works, 50 promises and works, but 9000 promises and explode..)
- I know that we have some solutions like, array.reduce(), loops, etc
- I know about the promises states (my array have pending promises initially)
My question: I can execute 20 promises, then another 20 promises, etc but... If im executing my promises sequentially, nodeJS must execute 9k promises without problem? I have a bad concept? My code is wrong?
(Im doubting because nodeJS wait some time before begin to resolve the promises)
My case: i trying download 9k+ images (with axios), then save each one and then wait 5 seconds sequentially.
[download 1 image, save that image, wait 5 seconds, then download next image, save.., wait..., etc.. ] Possible?
javascript node.js asynchronous promise axios
javascript node.js asynchronous promise axios
edited Jan 3 at 16:38
Armel
1,204920
1,204920
asked Jan 3 at 14:42
AndresSpAndresSp
2418
2418
2
So first question, why in the world would you want to chain 9000 promises? That is just poor design. Doesn't the api or tool you use offer bulk gets?
– basic
Jan 3 at 14:45
i cannot find any reasons for such an amount of promises
– messerbill
Jan 3 at 14:49
If we talk theoretically, did you try to config node to run with more memory?
– Maayao
Jan 3 at 14:51
1
I think Promise.all only care about if all promises was resolved, and allow execute in parallel, i tried it. Thanks
– AndresSp
Jan 3 at 15:00
1
Take a look at this npm package: npmjs.com/package/promise-queue
– Jaime
Jan 3 at 15:24
|
show 10 more comments
2
So first question, why in the world would you want to chain 9000 promises? That is just poor design. Doesn't the api or tool you use offer bulk gets?
– basic
Jan 3 at 14:45
i cannot find any reasons for such an amount of promises
– messerbill
Jan 3 at 14:49
If we talk theoretically, did you try to config node to run with more memory?
– Maayao
Jan 3 at 14:51
1
I think Promise.all only care about if all promises was resolved, and allow execute in parallel, i tried it. Thanks
– AndresSp
Jan 3 at 15:00
1
Take a look at this npm package: npmjs.com/package/promise-queue
– Jaime
Jan 3 at 15:24
2
2
So first question, why in the world would you want to chain 9000 promises? That is just poor design. Doesn't the api or tool you use offer bulk gets?
– basic
Jan 3 at 14:45
So first question, why in the world would you want to chain 9000 promises? That is just poor design. Doesn't the api or tool you use offer bulk gets?
– basic
Jan 3 at 14:45
i cannot find any reasons for such an amount of promises
– messerbill
Jan 3 at 14:49
i cannot find any reasons for such an amount of promises
– messerbill
Jan 3 at 14:49
If we talk theoretically, did you try to config node to run with more memory?
– Maayao
Jan 3 at 14:51
If we talk theoretically, did you try to config node to run with more memory?
– Maayao
Jan 3 at 14:51
1
1
I think Promise.all only care about if all promises was resolved, and allow execute in parallel, i tried it. Thanks
– AndresSp
Jan 3 at 15:00
I think Promise.all only care about if all promises was resolved, and allow execute in parallel, i tried it. Thanks
– AndresSp
Jan 3 at 15:00
1
1
Take a look at this npm package: npmjs.com/package/promise-queue
– Jaime
Jan 3 at 15:24
Take a look at this npm package: npmjs.com/package/promise-queue
– Jaime
Jan 3 at 15:24
|
show 10 more comments
1 Answer
1
active
oldest
votes
I would have used something like a worker pool instead of executing things in a batch of 20 each time, you will always end up waiting for the last one to finish before you start next 20 batch, instead you should set a limit of how many continious download you want to do so you have no more then 20 promises and not a long chain of 9000
The same thing can be accomplish with iterators also. (a same iterator can be passed to different workers and while someone calls the first item the next worker will always get the next one)
So with zero dependencies i would do something like this:
const sleep = n => new Promise(rs => setTimeout(rs, 1000))
async function sequentialDownload(iterator) {
for (let [index, url] of iterator) {
// figure out where to save the file
const path = path.resolve(__dirname, 'images', index + '.jpg')
// download all images as a stream
const res = await axios.get(index, { responseType: 'stream' })
// pipe the stream to disc
const writer = fs.createWriteStream(path)
res.data.pipe(writer)
// wait for the download to complete
await new Promise(resolve => writer.on('finish', resolve))
// wait a extra 5 sec
await sleep(5000)
}
}
const arr = [url1, url2, url3] // to be downloaded
const workers = new Array(20) // create 20 "workers"
.fill(arr.entries()) // fill it with same iterator
.map(sequentialDownload) // start working
Promise.all(workers).then(() => {
console.log('done downloading everything')
})
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1 Answer
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oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
I would have used something like a worker pool instead of executing things in a batch of 20 each time, you will always end up waiting for the last one to finish before you start next 20 batch, instead you should set a limit of how many continious download you want to do so you have no more then 20 promises and not a long chain of 9000
The same thing can be accomplish with iterators also. (a same iterator can be passed to different workers and while someone calls the first item the next worker will always get the next one)
So with zero dependencies i would do something like this:
const sleep = n => new Promise(rs => setTimeout(rs, 1000))
async function sequentialDownload(iterator) {
for (let [index, url] of iterator) {
// figure out where to save the file
const path = path.resolve(__dirname, 'images', index + '.jpg')
// download all images as a stream
const res = await axios.get(index, { responseType: 'stream' })
// pipe the stream to disc
const writer = fs.createWriteStream(path)
res.data.pipe(writer)
// wait for the download to complete
await new Promise(resolve => writer.on('finish', resolve))
// wait a extra 5 sec
await sleep(5000)
}
}
const arr = [url1, url2, url3] // to be downloaded
const workers = new Array(20) // create 20 "workers"
.fill(arr.entries()) // fill it with same iterator
.map(sequentialDownload) // start working
Promise.all(workers).then(() => {
console.log('done downloading everything')
})
add a comment |
I would have used something like a worker pool instead of executing things in a batch of 20 each time, you will always end up waiting for the last one to finish before you start next 20 batch, instead you should set a limit of how many continious download you want to do so you have no more then 20 promises and not a long chain of 9000
The same thing can be accomplish with iterators also. (a same iterator can be passed to different workers and while someone calls the first item the next worker will always get the next one)
So with zero dependencies i would do something like this:
const sleep = n => new Promise(rs => setTimeout(rs, 1000))
async function sequentialDownload(iterator) {
for (let [index, url] of iterator) {
// figure out where to save the file
const path = path.resolve(__dirname, 'images', index + '.jpg')
// download all images as a stream
const res = await axios.get(index, { responseType: 'stream' })
// pipe the stream to disc
const writer = fs.createWriteStream(path)
res.data.pipe(writer)
// wait for the download to complete
await new Promise(resolve => writer.on('finish', resolve))
// wait a extra 5 sec
await sleep(5000)
}
}
const arr = [url1, url2, url3] // to be downloaded
const workers = new Array(20) // create 20 "workers"
.fill(arr.entries()) // fill it with same iterator
.map(sequentialDownload) // start working
Promise.all(workers).then(() => {
console.log('done downloading everything')
})
add a comment |
I would have used something like a worker pool instead of executing things in a batch of 20 each time, you will always end up waiting for the last one to finish before you start next 20 batch, instead you should set a limit of how many continious download you want to do so you have no more then 20 promises and not a long chain of 9000
The same thing can be accomplish with iterators also. (a same iterator can be passed to different workers and while someone calls the first item the next worker will always get the next one)
So with zero dependencies i would do something like this:
const sleep = n => new Promise(rs => setTimeout(rs, 1000))
async function sequentialDownload(iterator) {
for (let [index, url] of iterator) {
// figure out where to save the file
const path = path.resolve(__dirname, 'images', index + '.jpg')
// download all images as a stream
const res = await axios.get(index, { responseType: 'stream' })
// pipe the stream to disc
const writer = fs.createWriteStream(path)
res.data.pipe(writer)
// wait for the download to complete
await new Promise(resolve => writer.on('finish', resolve))
// wait a extra 5 sec
await sleep(5000)
}
}
const arr = [url1, url2, url3] // to be downloaded
const workers = new Array(20) // create 20 "workers"
.fill(arr.entries()) // fill it with same iterator
.map(sequentialDownload) // start working
Promise.all(workers).then(() => {
console.log('done downloading everything')
})
I would have used something like a worker pool instead of executing things in a batch of 20 each time, you will always end up waiting for the last one to finish before you start next 20 batch, instead you should set a limit of how many continious download you want to do so you have no more then 20 promises and not a long chain of 9000
The same thing can be accomplish with iterators also. (a same iterator can be passed to different workers and while someone calls the first item the next worker will always get the next one)
So with zero dependencies i would do something like this:
const sleep = n => new Promise(rs => setTimeout(rs, 1000))
async function sequentialDownload(iterator) {
for (let [index, url] of iterator) {
// figure out where to save the file
const path = path.resolve(__dirname, 'images', index + '.jpg')
// download all images as a stream
const res = await axios.get(index, { responseType: 'stream' })
// pipe the stream to disc
const writer = fs.createWriteStream(path)
res.data.pipe(writer)
// wait for the download to complete
await new Promise(resolve => writer.on('finish', resolve))
// wait a extra 5 sec
await sleep(5000)
}
}
const arr = [url1, url2, url3] // to be downloaded
const workers = new Array(20) // create 20 "workers"
.fill(arr.entries()) // fill it with same iterator
.map(sequentialDownload) // start working
Promise.all(workers).then(() => {
console.log('done downloading everything')
})
answered Jan 3 at 15:25
EndlessEndless
12.8k65471
12.8k65471
add a comment |
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2
So first question, why in the world would you want to chain 9000 promises? That is just poor design. Doesn't the api or tool you use offer bulk gets?
– basic
Jan 3 at 14:45
i cannot find any reasons for such an amount of promises
– messerbill
Jan 3 at 14:49
If we talk theoretically, did you try to config node to run with more memory?
– Maayao
Jan 3 at 14:51
1
I think Promise.all only care about if all promises was resolved, and allow execute in parallel, i tried it. Thanks
– AndresSp
Jan 3 at 15:00
1
Take a look at this npm package: npmjs.com/package/promise-queue
– Jaime
Jan 3 at 15:24