Bus error crash in the new mg_wakeup() function about mongoose

[scaprile]

Mongoose needs to get that amount of memory from somewhere. If you expect to pass 1MB chunks, then you need at least a 1MB task stack. That function wasn't meant to be used with huge chunks of memory, you can change alloca for alloc and that memory will come out of your heap instead of your task stack. That may be great for your case but a penalty for typical applications passing a simple response.

[jvo203]

Yes I agree the memory has to come out of somewhere. As you say, either the stack needs to be made sufficiently large or that memory has to come from the heap.

Personally I don't send 1MB payloads 'as is'. As you are aware I send pointers to large payloads, pointers do not take up much memory so using alloca() is not a pressing problem.

If you think it's OK to close this issue without changing mongoose then it's absolutely OK with me too. It's just one thing to keep in mind when using mongoose, one needs to be aware of the stack size etc.

[scaprile]

@cpq I think we should keep things as they are. I can add a note on stack usage at the function entry in the API docs. IMO, having several allocs for small messages would be detrimental. We already have a note telling users to dimension their stack, they are just missing this new piece of information. WDYT ?

[cpq]

@jvo203 @scaprile

We should not send messages so big.
They are sent over UDP socketpair, which has its internal limit.
I am not sure that we should impose the limit in the code, let's change the documentation.

I've updated the docs, https://mongoose.ws/documentation/#mg_wakeup