Paralelizando promesas

Si necesitamos ejecutar muchas tareas asíncronas (imagina un arreglo de promesas) se convierte en una gran limitación no poder controlar la concurrencia de las operaciones con Promise.all. En esta charla veremos como podemos agregar la noción de concurrencia, throttling y manejo de errores para grupos de tareas modeladas como promesas.

Slides originales: https://docs.google.com/presentation/d/e/2PACX-1vTTXUEP7CCckZ4gefsnLe0DeYIbigf-7WwGrq76_VwTlp9qzV2xeB4gQZjZ2NYehViAeIjnnS09Mw2h/pub?start=false&loop=false&delayms=3000

Presentado en SantiagoJS el 13 Sep 2018: https://www.meetup.com/NodersJS/events/snrpwpyxmbrb/

Blog post en Medium: https://medium.com/laboratoria-developers/paralelizando-promesas-372894c1d21f

Transcript

1. @lupomontero SantiagoJS 13/09/2018
2. Director de tecnología @Laboratoriala Co-organizador @LimaJSorg
4. Delete user auth.deleteUser(uid) .then(console.log) .catch(console.error);
5. Promise.all (todos a la vez!) Promise.all(users.map(user => auth.deleteUser(user.localId))) .then(console.log) .catch(console.error);
6. { Error: An internal error has occurred. Raw server response: "{"error":{"code":400,"message":"QUOTA_EXCEEDED : Exceeded quota for deleting accounts.","errors":[{"message":"QUOTA_EXCEEDED : Exceeded quota for deleting accounts.","domain":"global","reason":"invalid"}]}}" at FirebaseAuthError.FirebaseError [as constructor] (/Users/lupo/work/lupomontero/paralelizando-promesas/node_modules/firebase-admin/lib/utils/error.js:39:28) at FirebaseAuthError.PrefixedFirebaseError [as constructor] (/Users/lupo/work/lupomontero/paralelizando-promesas/node_modules/firebase-admin/lib/utils/error.js:85:28) at new FirebaseAuthError (/Users/lupo/work/lupomontero/paralelizando-promesas/node_modules/firebase-admin/lib/utils/error.js:143:16) at Function.FirebaseAuthError.fromServerError (/Users/lupo/work/lupomontero/paralelizando-promesas/node_modules/firebase-admin/lib/utils/error.js:173:16) at /Users/lupo/work/lupomontero/paralelizando-promesas/node_modules/firebase-admin/lib/auth/auth-api-request.js:723 :45 at process._tickCallback (internal/process/next_tick.js:68:7) errorInfo: { code: 'auth/internal-error', message: 'An internal error has occurred. Raw server response: "{"error":{"code":400,"message":"QUOTA_EXCEEDED : Exceeded quota for deleting accounts.","errors":[{"message":"QUOTA_EXCEEDED : Exceeded quota for deleting accounts.","domain":"global","reason":"invalid"}]}}"' }, codePrefix: 'auth' } QUOTA_EXCEEDED : Exceeded quota for deleting accounts.
8. Requerimientos • No más de 10 tareas (invocaciones a auth.deleteUser()) por segundo. • Batches (grupos) de 10 • Intervalo entre batches (1 seg) • Si una tarea falla las demás deben continuar
9. Tareas vs promesas const promises = users.map(user => auth.deleteUser(user.localId)) const tasks = users.map(user => () => auth.deleteUser(user.localId))
10. En serie vs en paralelo
11. Series const series = (tasks, results = []) => ( (!tasks.length) ? Promise.resolve(results) : tasks[0]().then(result => series(tasks.slice(1), [...results, result])) );
12. Concurrency
13. Dividiendo arreglo en “batches” (grupos?) const splitArrayIntoBatches = (arr, limit) => arr.reduce((memo, item) => { if (memo.length && memo[memo.length - 1].length < limit) { memo[memo.length - 1].push(item); return memo; } return [...memo, [item]]; }, []);
14. const array = ['a', 'b', 'c', 'd', 'e']; splitArrayIntoBatches(array, 1); // => [['a'], ['b'], ['c'], ['d'], ['e']] splitArrayIntoBatches(array, 2); // => [['a', 'b'], ['c', 'd'], ['e']] splitArrayIntoBatches(array, 3); // => [['a', 'b', 'c'], ['d', 'e']] splitArrayIntoBatches(array, 4); // => [['a', 'b', 'c', 'd'], ['e']] splitArrayIntoBatches(array, 5); // => [['a', 'b', 'c', 'd', 'e']]
15. const batched = (tasks, concurrency) => { const processBatches = (batches, prevResults = []) => ( (!batches.length) ? Promise.resolve(prevResults) : Promise.all(batches[0].map(fn => fn())) .then(batchResults => processBatches(batches.slice(1), [ ...prevResults, ...batchResults, ])) ); return processBatches(splitArrayIntoBatches(tasks, concurrency)); };
16. // ejecuta todas las tareas de 5 en 5 batched(tasks, 5) .then(console.log) .catch(console.error);
17. Throttling
18. Agregando tiempo de espera entre lotes // Antes processBatches(batches.slice(1), results) // Después new Promise((resolve, reject) => setTimeout( () => processBatches(batches.slice(1), results) .then(resolve, reject), interval, ))
19. const throttled = (tasks, concurrency, interval = 0) => { const processBatches = (batches, prevResults = []) => { if (!batches.length) { return Promise.resolve(prevResults); } return Promise.all(batches[0].map(fn => fn())).then((batchResults) => { const results = [...prevResults, ...batchResults]; return (batches.length <= 1) ? results : new Promise((resolve, reject) => setTimeout( () => processBatches(batches.slice(1), results).then(resolve, reject), interval, )); }); }; return processBatches(splitArrayIntoBatches(tasks, concurrency)); };
20. // ejecuta tareas de 5 en 5, // esperando 1s entre cada lote throttled(tasks, 5, 1000) .then(console.log) .catch(console.error);
21. Error handling
22. // así procesábamos las tareas de un batch (en paralelo) Promise.all( batches[0].map(fn => fn()), ) // agregamos la opción `failFast` y manejamos errores cuando // `failFast` sea `false` Promise.all( batches[0].map(fn => (failFast ? fn() : fn().catch(err => err))), )
23. const pact = (tasks, concurrency, interval = 0, failFast = true) => { const processBatches = (batches, prevResults = []) => { if (!batches.length) { return Promise.resolve(prevResults); } return Promise.all( batches[0].map(fn => (failFast ? fn() : fn().catch(err => err))), ).then((batchResults) => { const results = [...prevResults, ...batchResults]; return (batches.length <= 1) ? results : new Promise((resolve, reject) => setTimeout( () => processBatches(batches.slice(1), results).then(resolve, reject), interval, )); }); }; return processBatches(splitArrayIntoBatches(tasks, concurrency)); };
24. pact(tasks, 5, 1000, false) .then(console.log);
25. Material complementario Código fuente: https://github.com/lupomontero/pact Blog post: https://medium.com/laboratoria-developers/p aralelizando-promesas-372894c1d21f
26. Gracias!