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Purpose
Abstractions:
-
ThreadLocalAccessor
- contract to assist with access to aThreadLocal
value. -
ContextAccessor
- contract to assist with access to aMap
-like context. -
ContextRegistry
- registry for instances ofThreadLocalAccessor
andContextAccessor
. -
ContextSnapshot
- holder of contextual values, that provides methods to capture and to propagate.
Example Scenarios:
-
In imperative code, e.g. Spring MVC controller, capture
ThreadLocal
values into aContextSnapshot
. After that use the snapshot to populate a ReactorContext
with the captured values, or to wrap a task (e.g.Runnable
,Callable
, etc) or anExecutor
with a decorator that restoresThreadLocal
values when the task executes. -
In reactive code, e.g. Spring WebFlux controller, create a
ContextSnapshot
from ReactorContext
values. After that use the snapshot to restoreThreadLocal
values within a specific stage (operator) of the reactive chain.
Context values can originate from any context mechanism and propagate to any other, any
number of times. For example, a value in a Reactor
context may originate as a
ThreadLocal
, and may yet become a ThreadLocal
again, and so on.
Generally, imperative code should interact with ThreadLocal
values as usual, and
likewise Reactor code should interact with the Reactor Context
as usual. The Context
Propagation library is not intended to replace those, but to assist with propagation when
crossing from one type of context to another, e.g. when imperative code invokes a Reactor
chain, or when a Reactor chain invokes an imperative component that expects
ThreadLocal
values.
The library is not limited to context propagation from imperative to reactive. It can
assist in asynchronous scenarios to propagate ThreadLocal
values from one thread to
another. It can also propagate to any other type of context for which there is a
registered ContextAccesor
instance.