marshaling (json) map element in struct thread safe?

[Samit Pal]

Hi,

I have a struct which has some nested struct elements. The nested structs are just wrappers around maps with a RWMutex each. The maps will be written to by multiple goroutines. I intend to marshal the struct using json.Marshal() to expose it via an http handler. The question is will the marshalling be thread safe.

Thanks
Samit

[Brad Fitzpatrick]

Nope. It's not safe to read from a map if another goroutine is writing to it.

The json marshalling code certainly won't use your RWMutex for you. (not that you were asking that)

You can verify that it's not safe by using the race detector.

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[Samit Pal]

I thought so. Thanks!

[Matt Harden]

You can write your own MarshalJSON methods for those structs to grab the read lock while doing the marshaling. The same goes for other serialiers like String.