Prepare ExecutionContext without prepare method

ec.scala

// Something like this will likely allow propagation of thread-local information

val originalEc: ExecutionContext = ... // the actual execution context
// This will get called every time an implicit EC is necessary, effectively preparing the context
implicit def wrappedEc: ExecutionContext = {
  val ctx = ...// capture thread local context here
  new ExecutionContext {
    override def execute(r: Runnable): Unit = originalEc.execute(new Runnable() {
      override def run(): Unit {
        val oldCtx = ... // get old context
        try {
          ... // restore captured context
          r.run()
        } finally {
          ... // restore old context
        }
      }
    })
  }
}

example.scala

// Just a silly example

implicit def myEc: ExecutionContext = {
    println("ec prepare")
    scala.concurrent.ExecutionContext.Implicits.global
}

Future(1).map(_ + 1).map(_ + 2).foreach(println)

// Output:
// ec prepare
// ec prepare
// ec prepare
// ec prepare
// 4