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v/examples/news_fetcher.v

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// Copyright (c) 2019 Alexander Medvednikov. All rights reserved.
// Use of this source code is governed by an MIT license
// that can be found in the LICENSE file.
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import http
import json
import sync
const (
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NR_THREADS = 4
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)
struct Story {
title string
url string
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}
struct Fetcher {
mut:
mu sync.Mutex
ids []int
cursor int
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wg &sync.WaitGroup
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}
fn (f mut Fetcher) fetch() {
for {
if f.cursor >= f.ids.len {
return
}
id := f.ids[f.cursor]
f.mu.lock()
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f.cursor++
f.mu.unlock()
cursor := f.cursor
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resp := http.get('https://hacker-news.firebaseio.com/v0/item/${id}.json') or {
println('failed to fetch data from /v0/item/${id}.json')
exit(1)
}
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story := json.decode(Story, resp.text) or {
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println('failed to decode a story')
exit(1)
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}
println('#$cursor) $story.title | $story.url')
f.wg.done()
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}
}
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// Fetches top HN stories in 4 coroutines
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fn main() {
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resp := http.get('https://hacker-news.firebaseio.com/v0/topstories.json') or {
println('failed to fetch data from /v0/topstories.json')
return
}
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mut ids := json.decode([]int, resp.text) or {
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println('failed to decode topstories.json')
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return
}
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if ids.len > 10 {
// ids = ids[:10]
mut tmp := [0].repeat(10)
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for i := 0 ; i < 10 ; i++ {
tmp[i] = ids[i]
}
ids = tmp
}
mut wg := &sync.WaitGroup{}
fetcher := &Fetcher{ids: ids, wg: wg} // wg sent via ptr
wg.add(ids.len)
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for i := 0; i < NR_THREADS; i++ {
go fetcher.fetch()
}
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wg.wait()
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}