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import java.util.{Map => JMap}
import com.twitter.inject.logging.MDCInitializer
import org.slf4j.MDC
import scala.concurrent.ExecutionContext
* An `ExecutionContext` which takes the calling thread's MDC context map and copies it into
* the thread of where the runnable will be executed. As the `prepare` method of `ExecutionContext`
* is deprecated, it is advised to capture thread local data when the `ExecutionContext` is created.
* As a result of this, this `ExecutionContext` should not be stored as a `val` as it will not
* update the MDC value on each run.
object MdcPropagatingExecutionContext {
def apply(underlying: ExecutionContext): ExecutionContext = new ExecutionContext {
private val context: JMap[String, String] = MDC.getCopyOfContextMap
override def execute(r: Runnable): Unit = {
val previousContext = MDC.getCopyOfContextMap
underlying.execute(() => {
MDCInitializer.let {
try {
} finally {
private def setMdcContext(context: JMap[String, String]): Unit =
if (context != null) MDC.setContextMap(context) else MDC.clear()
override def reportFailure(t: Throwable): Unit = underlying.reportFailure(t)
object Implicits {
* Wrapper around the global execution context. Needs to be a `def` so that each call to it uses the
* current thread's MDC values.
implicit def global: ExecutionContext = MdcPropagatingExecutionContext(
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