4 ms·

var buttons = []string{"red", "blue", "green", "yellow", "purple"} > go run level_9.go Sending Code Sequence... 1 : red 2 : blue 3 : green

var buttons = []string{"red", "blue", "green", "yellow", "purple"} > go run level_9.go Sending Code Sequence... 1 : red 2 : blue 3 : green 4 : yellow 5 : purple Sorry, that's not correct Not sure what the correct sequence is, if not that?

bemidji 7y ago
What are the concurrency guarantees of goroutines? ;)
- DuskStar 7y ago
  I'm confused here too - is there some other desired behavior? I thought the goal here was to avoid race conditions and just reproduce that order, since that's what's in the source code... > var buttons = []string{"red", "blue", "green", "yellow", "purple"}
- Thorrez 7y ago
  There are none, right? So even if you add mutexes to the existing code in an attempt to remove race conditions, it will still have race conditions, and have no guaranteed output order, because you have no guarantee which order the goroutines will start in. The obvious way to solve it in order to get the answer shown in the source code is if x == 0 { *sequence = []Button{{"red"}, {"blue"}, {"green"}, {"yellow"}, {"purple"}} } return This way there is nothing concurrently touching sequence, nor is there anything concurrent touching rand, nor is anything relying on goroutine starting order, nor are there other race conditions. But yet the site says this is wrong.
  - everdev 7y ago
    You can click the lightbulb to get a hint. The way I solved it was with a Mutex.
    - Thorrez 7y ago
      Yeah I know about the hint. But the result the hint leads you to doesn't make sense. Using a Mutex removes data races, but it does not remove race conditions. By leaving the race condition in, the code is has output that cannot be relied on. But yet the challenge wants us to think that somehow the output has a specific value that can be relied on.
  - AlexCoventry 7y ago
    It turns out there is a guaranteed order, because of the way this puzzle is executed. https://bit.ly/2rqqWkh https://bit.ly/2rqqWkh
    - Thorrez 7y ago
      Where is this guarantee stated? I don't see anything on that page about a guarantee. Does the go spec make this guarantee? How do we know how the puzzle is executed? And if you're saying some guarantee exists that the last executes first, then the rest execute in order, that's empirically false: https://play.golang.org/p/3gV0TYG4GQW https://play.golang.org/p/3gV0TYG4GQW 1000 773 774 775 776 ...
      - AlexCoventry 7y ago
        I'm not saying it's a good guarantee.
re 7y ago
The story is a little misleading -- the correct sequence is not in fact "sitting right there in the code." I "cheated" on some questions by causing the correct output to be printed without actually doing what the instructions recommend, but in this case, the path of the least resistance is probably to follow the instructions, including leveraging what the lightbulb hint recommends. Additional Hint 1: Tbebhgvarf nera'g arprffnevyl rkrphgrq va gur beqre gung gurl'er fgnegrq Additional Hint 2: Qb nf gur vafgehpgvbaf naq uvag fhttrfg naq svk gur enpr pbaqvgvba ol hfvat n zhgrk gb rafher gung bayl bar tbebhgvar ng n gvzr fyrrcf naq gura nccraqf gb gur neenl Additional Hint 3: Lbh pna eranzr gur frgOhggba zrgubq naq znxr lbhe bja ercynprzrag gung pnyyf gur byq bar If you want to "cheat": hfr lbhe oebjfre pbafbyr gb frr gur .tb svyrf gung ner ybnqrq juvpu pbagnva gur fgbel, pbqr, naq pbeerpg bhgchg. Decode hints with https://rot13.com/ https://rot13.com/
- DuskStar 7y ago
  Thanks for the help! Though I would have phrased the first hint as "Gur qrfverq beqre vf gur beqre va juvpu gur tbebhgvarf ner rkrphgrq"
- AlexCoventry 7y ago
  Another hint, a reddit discussion of a golang phenomenon this puzzle depends on: https://bit.ly/2rqqWkh https://bit.ly/2rqqWkh It's a bit annoying that it's depending on such an incidental behavior.
- fred256 7y ago
  My initial solution for this was to sleep 20*x milliseconds in setButton. Because the later random sleep is up to 10 milliseconds this ensures that the operations are always done in the defined order. But I guess that's not what they were after, the solution was indeed as simple as: z.Ybpx() qrsre z.Haybpx()

bemidji 7y ago

What are the concurrency guarantees of goroutines? ;)

DuskStar 7y ago
I'm confused here too - is there some other desired behavior? I thought the goal here was to avoid race conditions and just reproduce that order, since that's what's in the source code... > var buttons = []string{"red", "blue", "green", "yellow", "purple"}
Thorrez 7y ago
There are none, right? So even if you add mutexes to the existing code in an attempt to remove race conditions, it will still have race conditions, and have no guaranteed output order, because you have no guarantee which order the goroutines will start in. The obvious way to solve it in order to get the answer shown in the source code is if x == 0 { *sequence = []Button{{"red"}, {"blue"}, {"green"}, {"yellow"}, {"purple"}} } return This way there is nothing concurrently touching sequence, nor is there anything concurrent touching rand, nor is anything relying on goroutine starting order, nor are there other race conditions. But yet the site says this is wrong.
- everdev 7y ago
  You can click the lightbulb to get a hint. The way I solved it was with a Mutex.
  - Thorrez 7y ago
    Yeah I know about the hint. But the result the hint leads you to doesn't make sense. Using a Mutex removes data races, but it does not remove race conditions. By leaving the race condition in, the code is has output that cannot be relied on. But yet the challenge wants us to think that somehow the output has a specific value that can be relied on.
- AlexCoventry 7y ago
  It turns out there is a guaranteed order, because of the way this puzzle is executed. https://bit.ly/2rqqWkh https://bit.ly/2rqqWkh
  - Thorrez 7y ago
    Where is this guarantee stated? I don't see anything on that page about a guarantee. Does the go spec make this guarantee? How do we know how the puzzle is executed? And if you're saying some guarantee exists that the last executes first, then the rest execute in order, that's empirically false: https://play.golang.org/p/3gV0TYG4GQW https://play.golang.org/p/3gV0TYG4GQW 1000 773 774 775 776 ...
    - AlexCoventry 7y ago
      I'm not saying it's a good guarantee.

re 7y ago

The story is a little misleading -- the correct sequence is not in fact "sitting right there in the code." I "cheated" on some questions by causing the correct output to be printed without actually doing what the instructions recommend, but in this case, the path of the least resistance is probably to follow the instructions, including leveraging what the lightbulb hint recommends. Additional Hint 1: Tbebhgvarf nera'g arprffnevyl rkrphgrq va gur beqre gung gurl'er fgnegrq Additional Hint 2: Qb nf gur vafgehpgvbaf naq uvag fhttrfg naq svk gur enpr pbaqvgvba ol hfvat n zhgrk gb rafher gung bayl bar tbebhgvar ng n gvzr fyrrcf naq gura nccraqf gb gur neenl Additional Hint 3: Lbh pna eranzr gur frgOhggba zrgubq naq znxr lbhe bja ercynprzrag gung pnyyf gur byq bar If you want to "cheat": hfr lbhe oebjfre pbafbyr gb frr gur .tb svyrf gung ner ybnqrq juvpu pbagnva gur fgbel, pbqr, naq pbeerpg bhgchg. Decode hints with https://rot13.com/ https://rot13.com/

DuskStar 7y ago
Thanks for the help! Though I would have phrased the first hint as "Gur qrfverq beqre vf gur beqre va juvpu gur tbebhgvarf ner rkrphgrq"
AlexCoventry 7y ago
Another hint, a reddit discussion of a golang phenomenon this puzzle depends on: https://bit.ly/2rqqWkh https://bit.ly/2rqqWkh It's a bit annoying that it's depending on such an incidental behavior.
fred256 7y ago
My initial solution for this was to sleep 20*x milliseconds in setButton. Because the later random sleep is up to 10 milliseconds this ensures that the operations are always done in the defined order. But I guess that's not what they were after, the solution was indeed as simple as: z.Ybpx() qrsre z.Haybpx()