[英]Resolve a list of Javascript Promises - in sequence?
我的实际代码非常复杂,但我会尽可能简化:
let counter = 0
console.log("time counter: ", counter)
setInterval(() => {
counter = counter + 1;
console.log("time counter: ", counter)
}, 1000)
const myPromises =
[ new Promise((resolve, reject) => setTimeout(() => {
console.log("reject(1)")
reject(1)
}, 5 * 1000)) // after 5 seconds.
, new Promise(resolve => setTimeout(() => {
console.log("resolve(2)")
resolve(2)
}, 3 * 1000)) // after 3 seconds.
, new Promise(resolve => setTimeout(() => {
console.log("resolve(3)")
resolve(3)
}, 3 * 1000)) // after 3 seconds.
, new Promise((resolve, reject) => setTimeout(() => {
console.log("reject(4)")
reject(4)
}, 1 * 1000)) // after 1 second.
]
async function testIt(){
const results = myPromises.map(async promise => {
return new Promise((resolve) => {
// no matter what happens with the individual promise itself, we resolve.
promise
.then(ok => {
resolve({ wasSuccessful: true, result: ok })
})
.catch(err => {
resolve({ wasSuccessful: false, error: err })
})
})
})
// should be no need to catch anything here. use await.
const results_ = await Promise.all(results)
console.log("results_: ", results_)
}
testIt()
.catch(err => console.log("this error isn't supposed to happen error: ", err))
我基本上想要以下内容:
1. start the first promise( myPromises[0] ). Wait 5 seconds. After that reject it.
2. start the next promise( myPromises[1] ). Wait 3 seconds. Resolve it.
在这一点上,我们有 8 秒的时间。
3. start the next promise( myPromises[2] ). Wait another 3 seconds. Resolve it.
在这一点上,我们有 8 + 3 = 11 秒的计数器。
4. start the next promise ( myPromises[3] ).. Wait for 1 second.. resolve it.
我猜你的想法是 go .. 现在该怎么做?
请注意,这不是then().then().then()
..我没有减少/累积此列表,正如我在有关此主题的其他问题中看到的那样。 我不希望以任何理由拒绝这个。
相反,我想要一个结果列表。 像这样:
results_: [
{ wasSuccessful: false, error: 1 },
{ wasSuccessful: true, result: 2 },
{ wasSuccessful: true, result: 3 },
{ wasSuccessful: false, error: 4 }
]
但请注意我的 console.log output .. 即使我得到正确的结果,它也显示了真正的执行顺序:
time counter: 0
time counter: 1
resolve(4)
time counter: 2
resolve(2)
resolve(3)
time counter: 3
time counter: 4
reject(1)
results_: [
{ wasSuccessful: false, error: 1 }, // note the array ordering is correct. rejected,
{ wasSuccessful: true, result: 2 }, // resolved,
{ wasSuccessful: true, result: 3 }, // resolved,
{ wasSuccessful: false, error: 4 } // rejected. good.
]
time counter: 5
time counter: 6
time counter: 7
基本上,这个承诺是并行触发的,无论哪个超时更快,都会更快地解决。
相反,我希望它是这样的:
time counter: 0
time counter: 1
time counter: 2
time counter: 3
time counter: 4
time counter: 5
reject(1)
time counter: 6
time counter: 7
time counter: 8
resolve(2)
time counter: 9
time counter: 10
time counter: 11
resolve(3)
time counter: 12
resolve(4)
results_: [
{ wasSuccessful: false, error: 1 },
{ wasSuccessful: true, result: 2 },
{ wasSuccessful: true, result: 3 },
{ wasSuccessful: false, error: 4 }
]
time counter: 13
time counter: 14
...
这是简化。 在实践中,我有 30k+ 记录的列表——我需要在这些记录上执行一些 api 操作,并从根本上解决 promise。 我将此列表分组为每个 10 个元素的子列表。 我将并行运行每个子列表。
但是大列表..又名列表列表..需要顺序:
bigList = [ [ small parallel list 0 ], [ small parallel list 1 ] .. ]
这个并行的每个 promise 已经非常计算密集。 如果我可以并行运行 10 个,我很幸运。 所以这就是为什么大列表必须是连续的。 否则它会触发一棵带有 30k 叶子的承诺树,这会导致某些东西崩溃。
仍然不确定这个规模是否现实,但在我实施这个序列之后,我将能够确定。
那么如何依次运行上面的这 4 个 Promise 呢? 谢谢。
所有这些承诺同时开始,所以你并行运行它们
您可以只在数组中使用 promise 的executor
程序 function - 然后在reduce
而不是map
中运行执行程序
let counter = 0 console.log("time counter: ", counter) let int = setInterval(() => { counter = counter + 1; console.log("time counter: ", counter) }, 1000) setTimeout(() => clearInterval(int), 15000); const myPromiseExecutors = [ (resolve, reject) => setTimeout(() => { console.log("reject(1)") reject(1) }, 5 * 1000) // after 5 seconds. , resolve => setTimeout(() => { console.log("resolve(2)") resolve(2) }, 3 * 1000) // after 3 seconds. , resolve => setTimeout(() => { console.log("resolve(3)") resolve(3) }, 3 * 1000) // after 3 seconds. , (resolve, reject) => setTimeout(() => { console.log("reject(4)") reject(4) }, 1 * 1000) // after 1 second. ] async function testIt(){ const results = await myPromiseExecutors.reduce(async (promise, exec) => { const ret = await promise; try { const ok = await new Promise(exec); ret.push({ wasSuccessful: true, result: ok }); } catch(err) { ret.push({ wasSuccessful: false, error: err }); } return ret; }, Promise.resolve([])) console.log("results_: ", results) } testIt();
老实说,使用for...of
循环可能会更干净
let counter = 0 console.log("time counter: ", counter) let int = setInterval(() => { counter = counter + 1; console.log("time counter: ", counter) }, 1000) setTimeout(() => clearInterval(int), 15000); const myPromiseExecutors = [ (resolve, reject) => setTimeout(() => { console.log("reject(1)") reject(1) }, 5 * 1000) // after 5 seconds. , resolve => setTimeout(() => { console.log("resolve(2)") resolve(2) }, 3 * 1000) // after 3 seconds. , resolve => setTimeout(() => { console.log("resolve(3)") resolve(3) }, 3 * 1000) // after 3 seconds. , (resolve, reject) => setTimeout(() => { console.log("reject(4)") reject(4) }, 1 * 1000) // after 1 second. ] async function testIt(){ const results = []; const p = Promise.resolve(); for (let exec of myPromiseExecutors) { try { const ok = await new Promise(exec); results.push({ wasSuccessful: true, result: ok }); } catch(err) { results.push({ wasSuccessful: false, error: err }); } } console.log("results_: ", results) } testIt();
只是一些伪代码来解决您的实际问题。 fn
是您要执行的操作,它应该返回 Promise。
async function run_in_chunks(fn, records, chunk_size) {
for (let chunk of chunkify(records, chunk_size))
await run_parallel(fn, chunk)
}
async function run_parallel(fn, records) {
await Promise.all(records.map(r => run_and_handle_error(fn, r)))
}
async function run_and_handle_error(fn, record) {
try {
await fn(record)
log_success(record)
} catch(e) {
log_error(record)
}
}
现有答案提供了您可以使用的“手工”解决方案。 但对于您的情况,我认为这种方法可以满足您的所有需求: https://caolan.github.io/async/v3/docs.html#parallelLimit
你给它 30k 记录的列表和“限制” - 即 10,这意味着它总是保持 10 个任务执行(一旦完成它就会启动另一个)。
如果您需要使用 Promise,请记住,一旦您创建 promise,它就会开始在后台执行并且您无法控制它,因此您需要某种“工厂”方法。 这意味着方法在执行时会创建 Promise。
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