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Comment by alphaalpha101 | Hacker News Reader

So this new concurrent map? Am I right in understanding it's designed for cases where you have a map shared between goroutines but where each goroutine essentially owns some subset of the keys in the map?

So basically it's designed for cases like 'I have N goroutines and each one owns 1/N keys'?

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> each goroutine essentially owns some subset of the keys in the map

With those constraints, why not create a small map for each goroutine at that point, and merge the maps afterwards?

Then you have to merge them on every read (after any modification).

This lightning talk gives some great information on use cases for the new sync.Map: https://youtu.be/C1EtfDnsdDs

Wow great find!

It could just be one map shared by many goroutines, which normally causes a panic:

    fatal error: concurrent map writes

i am dealing with this problem right now. also i have a big problem with deepclone,

I did a big rewrite of a current project, and clearly it was badly designed :(

Standard practice is to use a mutex to guard against concurrent usage.

also necessary for reads?

Also, do you have any good references to proper best practices around concurrent and parallel programming? (in Go.) Like just basic things. Code I can copy and paste without it having obscure race conditions because that use of mutex is absolutely correct, and something that lets me understand the limitations. I feel like it is very easy to do things "wrong" or not notice some edge cases. In C++ I didn't only ever coded single-threaded for this reason. Too many gotchas. Any help would be appreciated.

Necessary for reads unless no additional writing will be done. If you initialize/write into a map and then later have concurrent reads from it, the program will run. If you try to write in the midst of this, it will crash.

I would suggest you to read the book "Concurrency in Go", by Katherine Cox-Budai, 2017: http://shop.oreilly.com/product/0636920046189.do

Thank you for the recommendation!

I really, really don't understand why this would get downvoted. Are people not allowed to ask questions now?

They're discouraged from complaining about downvoting.

It was not a complaint, it was a question, just like my top-level comment.

Was that interpreted as a complaint as well? Is that the problem?

A concurrent map in my understanding, is a map that can be accessed concurrently without explicit synchronization, not each coroutine has a piece of it. Check java ConcurrentHashMap.

It sounded like complaining but either way, take a look at these.

https://news.ycombinator.com/newsguidelines.html

"Please don't comment about the voting on comments. It never does any good, and it makes boring reading."

or you just have two or more goroutines that need to modify a map

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