Pass a copy of the main coroutine context to the subroutine context

In PHP, coroutine is a powerful programming tool that can improve the execution efficiency of code. In coroutines, it is a common operation to pass a copy of the main coroutine context to the subroutine context. In this way, the context data of the main coroutine can be accessed in the subroutine to realize data sharing and transfer. This process is very simple in PHP, and you only need to use the yield keyword. In this article, we will introduce to you in detail how to pass a copy of the main coroutine context to the subroutine context, and give you some example code to help you better understand and apply this feature.

Question content

I have a golang API endpoint and its associated context.

The endpoint needs to do some heavy lifting behind the scenes, so I create a new subroutine inside the main endpoint and then return the response itself.

To handle context cancellation, I create a background context and pass it to the subroutine as a new context.

The problem is that by doing this, yes I can execute the background subroutine, but the values ​​in the main context, such as request ID, span ID, etc. (most of the keys I don't know), are used for tracing will be lost.

How to pass parent context to child routine without canceling execution even after response is sent to client.

edit

I'm not passing any value into the context. But initially we are passing the request-id, span-id, etc. required for tracking. This information is all in context. This is an internal library and the context is where we save it.

I know this is an anti-pattern of passing values ​​using context, no value will be passed except the request ID and other values ​​that are important to the library and not the business logic

Workaround

When you cancel a parent context, all contexts derived from it will also be cancelled. So you are correct to create a new context for the goroutine generated by the request handler.

When you create a new context, you should copy all the values ​​you are interested in from the original context to the new context. However, you say you don't know all the keys. Therefore, you can still keep a reference to the parent context so that it can be queried for its value. Something like this:

type nestedContext struct {
   context.Context
   parent context.Context
}

func (n nestedContext)  Value(key any) any {
   return n.parent.Value(key)
}

...
newContext := nestedContext{
   Context:context.Background(),
   parent: parentContext,
}

This will create a new context from context.background() which will look up the value from the canceled parent context.

Pass newcontext as the context to the goroutine created from the handler.

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