lab8.2 async serial exec with util modul
Hello,
In the lab 8.2 we have to run serialy (i am not sure we say like it, means serial execution) 3 async func.
I guess we should use "Promisify" as the util module is already import in the question.
But i don't get how to use it.
i can run the code without promisify
opA((err, d) => { print(err, d) opB((e, d) => { print(e, d) opC((e,d) => { print(e, d) }) }) })
i can run it with promise
function read(x) { return new Promise((resolve, reject) => { x((e,d) => { if(e) reject(print(e)) resolve(print(null, d)) }) }) } async function as() { await read(opA) await read(opB) await read(opC) } as()
But i don t understand how to run it with Promisify ???
i can promisify,
const a = promisify(opA) const b = promisify(opB) const c = promisify(opC)
But it does not work inside async/await, and it does not resolve, so i can not use .then().
So what am i missing, what is the point of promisify here ??
Using it with function returning promise like readFile(), i understand how it works. But in this case, using it with call-back, i don t.
Thanks if someone can explain.
Regards
ps; the code to run
const { promisify } = require('util') const print = (err, contents) => { if (err) console.error(err) else console.log(contents) } const opA = (cb) => { setTimeout(() => { cb(null, 'A') }, 500) } const opB = (cb) => { setTimeout(() => { cb(null, 'B') }, 250) } const opC = (cb) => { setTimeout(() => { cb(null, 'C') }, 125) }
Answers
-
I think the error handling is the part that's tripping you up:
SPOILERS - see for code
Given your `a`, `b` and `c` references: ``` async function as() { try { print(null, await a()) print(null, await b()) print(null, await c()) } catch (err) { print(err) } } ```When an awaited promise rejects in an async function it can be handled in a catch block.
In the above only the first to error will print and then execution will stop. If you wanted
to proceed if there's an error then you'd need to try catch each one. Either way is fine
for this exercise.0 -
Thank you very much, i got it.
ps. and Thanks for the course, It's great.
0 -
@djedje excellent!
0
Categories
- All Categories
- 112 LFX Mentorship
- 112 LFX Mentorship: Linux Kernel
- 604 Linux Foundation IT Professional Programs
- 315 Cloud Engineer IT Professional Program
- 139 Advanced Cloud Engineer IT Professional Program
- 52 DevOps Engineer IT Professional Program
- 67 Cloud Native Developer IT Professional Program
- 3 Express Training Courses
- 3 Express Courses - Discussion Forum
- 5.3K Training Courses
- 17 LFC110 Class Forum - Discontinued
- 8 LFC131 Class Forum
- 30 LFD102 Class Forum
- 178 LFD103 Class Forum
- LFD110 Class Forum
- 24 LFD121 Class Forum
- LFD133 Class Forum
- 2 LFD137 Class Forum
- 62 LFD201 Class Forum
- 2 LFD210 Class Forum
- 1 LFD210-CN Class Forum
- 1 LFD213 Class Forum - Discontinued
- 127 LFD232 Class Forum - Discontinued
- LFD233 Class Forum
- LFD237 Class Forum
- 22 LFD254 Class Forum
- 643 LFD259 Class Forum
- 107 LFD272 Class Forum
- 1 LFD272-JP クラス フォーラム
- 4 LFD273 Class Forum
- 1 LFS101 Class Forum
- LFS112 Class Forum
- LFS116 Class Forum
- LFS118 Class Forum
- LFS144 Class Forum
- 2 LFS145 Class Forum
- LFS151 Class Forum
- LFS157 Class Forum
- LFS158 Class Forum
- LFS162 Class Forum
- LFS167 Class Forum
- 28 LFS200 Class Forum
- 735 LFS201 Class Forum - Discontinued
- 1 LFS201-JP クラス フォーラム
- 13 LFS203 Class Forum
- 98 LFS207 Class Forum
- 299 LFS211 Class Forum
- 54 LFS216 Class Forum
- 47 LFS241 Class Forum
- 41 LFS242 Class Forum
- 36 LFS243 Class Forum
- 12 LFS244 Class Forum
- LFS245 Class Forum
- 41 LFS250 Class Forum
- 1 LFS250-JP クラス フォーラム
- LFS251 Class Forum
- 141 LFS253 Class Forum
- LFS254 Class Forum
- LFS255 Class Forum
- 2 LFS256 Class Forum
- LFS257 Class Forum
- 1.1K LFS258 Class Forum
- 9 LFS258-JP クラス フォーラム
- 109 LFS260 Class Forum
- 144 LFS261 Class Forum
- 39 LFS262 Class Forum
- 82 LFS263 Class Forum - Discontinued
- 15 LFS264 Class Forum - Discontinued
- 11 LFS266 Class Forum - Discontinued
- 20 LFS267 Class Forum
- 18 LFS268 Class Forum
- 26 LFS269 Class Forum
- 198 LFS272 Class Forum
- 1 LFS272-JP クラス フォーラム
- LFS274 Class Forum
- 3 LFS281 Class Forum
- 254 LFW211 Class Forum
- 173 LFW212 Class Forum
- 9 SKF100 Class Forum
- SKF200 Class Forum
- 781 Hardware
- 198 Drivers
- 68 I/O Devices
- 37 Monitors
- 95 Multimedia
- 174 Networking
- 87 Printers & Scanners
- 83 Storage
- 742 Linux Distributions
- 80 Debian
- 66 Fedora
- 15 Linux Mint
- 13 Mageia
- 23 openSUSE
- 143 Red Hat Enterprise
- 31 Slackware
- 13 SUSE Enterprise
- 347 Ubuntu
- 450 Linux System Administration
- 31 Cloud Computing
- 69 Command Line/Scripting
- Github systems admin projects
- 89 Linux Security
- 76 Network Management
- 101 System Management
- 46 Web Management
- 51 Mobile Computing
- 18 Android
- 23 Development
- 1.2K New to Linux
- 1K Getting Started with Linux
- 355 Off Topic
- 109 Introductions
- 167 Small Talk
- 18 Study Material
- 504 Programming and Development
- 283 Kernel Development
- 203 Software Development
- 844 Software
- 210 Applications
- 180 Command Line
- 3 Compiling/Installing
- 107 Games
- 308 Installation
- 51 All In Program
- 51 All In Forum
Upcoming Training
-
August 20, 2018
Kubernetes Administration (LFS458)
-
August 20, 2018
Linux System Administration (LFS301)
-
August 27, 2018
Open Source Virtualization (LFS462)
-
August 27, 2018
Linux Kernel Debugging and Security (LFD440)