How can I share some value without sharing Context.Key object instance?

[hojongs]

Summary

How can I store and get a value from Context without sharing Context.Key instance?

Detail

I want to share some value with grpc Context. but I can't get the stored value with Context.Key instance

I tried this snippet

Context.key("A") == Context.key("A")

The result was

false

But I expected

true

It means if I want to get value from a Context, I should use same Context.Key instance.
It is strange. Because, I'm trying to share some values with Context and when I get the stored value I should use same Context.Key.
To share some value, should share the key object instance. (not the key value)

For example (with kotlin)

// Function A
val myKey = Context.key("myKey")

Context.current()
    .withValue(key, "myVal")
    .attach()

// Function B, After call A
Context.key<String>("myKey").get() // == null // I think, It should be "myVal"

myKey.get() // == "myVal" 

If I can share myKey object instance, I don't need Context to share value.
What about multi-threaded case? It is more difficult to share the Context.Key object instance.

I can't understand use of Context and Context.key to share value.

In short, My question is.

How can I store and get a value from Context without sharing Context.Key instance?

[ericgribkoff]

You're correct that multiple Context.Key can share the same debug name but still won't return true when tested for equality. From the doc at https://grpc.github.io/grpc-java/javadoc/io/grpc/Context.html#key-java.lang.String-:

Create a Context.Key with the given debug name. Multiple different keys may have the same name; the name is intended for debugging purposes and does not impact behavior.

You need to use the same Context.Key reference when inserting and retrieving values from the context. A simple way to achieve this is to create your key as essentially a global constant and use it when setting and retrieving values. I didn't look through it carefully but https://github.com/saturnism/grpc-by-example-java/tree/master/metadata-context-example shows example code that uses Context.Key to propagate values.

[hojongs]

Thank you for your answer. I was missing the doc of Context.key API.
I understood of the way to use it for my purpose.
But I think it is confuse still.
Generally, key's name will be recognized it is identifier by people (In my opinion)
the name parameter of Context.key(name) is debugging name, so Let me give a suggestion.

• Make Context.key(name) function have default parameter value
  • or overload key function without any parameter.
  • It represents the name parameter is optional.

  public static <T> Key<T> key() {
    return new Key<>(DEFAULT_KEY_NAME);
  }

[ericgribkoff]

Since the question here is resolved, I'm going to mark this issue as closed (discussion on the updates can continue on the PR). Thanks!