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Preserve the MDC context during callbacks. #5

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Preserve the MDC context during callbacks. #5

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27 changes: 27 additions & 0 deletions src/Deferred.java
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Original file line number Diff line number Diff line change
Expand Up @@ -28,9 +28,11 @@
import java.util.ArrayList;
import java.util.Collection;
import java.util.concurrent.atomic.AtomicIntegerFieldUpdater;
import java.util.Map;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.slf4j.MDC;

/**
* A thread-safe implementation of a deferred result for easy asynchronous
Expand Down Expand Up @@ -570,6 +572,12 @@ public final class Deferred<T> {
private static final AtomicIntegerFieldUpdater<Deferred> stateUpdater =
AtomicIntegerFieldUpdater.newUpdater(Deferred.class, "state");

/**
* Captures the current context map of the current thread. This map is later
* reconstituted on the thread that begins the callback chain.
*/
private final Map mdcContext = MDC.getCopyOfContextMap();

/**
* Atomically compares and swaps the state of this Deferred.
* @param cmp The expected state to compare against.
Expand Down Expand Up @@ -1223,10 +1231,28 @@ public String toString() {
}
};

/**
* Sets the MDC context to the given {@code map}. It returns the original map
* that was in effect before the call took place. If {@code map} is null, the
* MDC context is cleared.
* @param map The context map to set.
* @return the original map that was in effect before this call took place.
*/
private Map setMdc(Map map) {
Map old = MDC.getCopyOfContextMap();
if (map != null) {
MDC.setContextMap(map);
} else {
MDC.clear();
}
return old;
}

/**
* Executes all the callbacks in the current chain.
*/
private void runCallbacks() {
Map old = setMdc(mdcContext);
while (true) {
Callback cb = null;
Callback eb = null;
Expand Down Expand Up @@ -1263,6 +1289,7 @@ private void runCallbacks() {
// + "), result=" + result
// + " in " + (System.nanoTime() - start) / 1000 + "us");
}
setMdc(old);
}

/**
Expand Down