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[WIP] DistinctErrorLog lock free. #325

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[WIP] DistinctErrorLog lock free. #325

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71 changes: 58 additions & 13 deletions agrona/src/main/java/org/agrona/concurrent/errors/DistinctErrorLog.java
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Original file line number Diff line number Diff line change
Expand Up @@ -97,7 +97,7 @@ public class DistinctErrorLog
private final EpochClock clock;
private final AtomicBuffer buffer;
private final Charset charset;
private DistinctObservation[] distinctObservations = new DistinctObservation[0];
private volatile DistinctObservation[] distinctObservations = new DistinctObservation[0];

/**
* Create a new error log that will be written to a provided {@link AtomicBuffer}.
Expand Down Expand Up @@ -157,38 +157,83 @@ public Charset charset()
*/
public boolean record(final Throwable observation)
{
final long timestampMs;
DistinctObservation distinctObservation;
final long timestampMs = clock.time();
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I think the above logic should be moved into the updateLastObservationTimestamp method.


timestampMs = clock.time();
synchronized (this)
DistinctObservation distinctObservation;
DistinctObservation[] currentDistinctObservations;
int searchIndex = 0;
for (; ; )
{
distinctObservation = find(distinctObservations, observation);
currentDistinctObservations = this.distinctObservations;
distinctObservation = find(currentDistinctObservations, searchIndex, observation);
searchIndex = currentDistinctObservations.length;

if (null == distinctObservation)
if (distinctObservation != null)
{
// A distinctObservation was found
break;
}
else if (currentDistinctObservations == distinctObservations)
{
distinctObservation = newObservation(timestampMs, observation);
if (INSUFFICIENT_SPACE == distinctObservation)
// A distinctObservation was not found, and now an attempt is made to create the new observation
synchronized (this)
{
return false;
// One more find is needed, because it could be a new observation was added prior to
// obtaining the lock.
if (currentDistinctObservations != distinctObservations)
{
distinctObservation = find(distinctObservations, searchIndex, observation);
}

if (null == distinctObservation)
{
distinctObservation = newObservation(timestampMs, observation);
if (INSUFFICIENT_SPACE == distinctObservation)
{
return false;
}
}
}

break;
}
}

final int offset = distinctObservation.offset;
buffer.getAndAddInt(offset + OBSERVATION_COUNT_OFFSET, 1);
buffer.putLongRelease(offset + LAST_OBSERVATION_TIMESTAMP_OFFSET, timestampMs);

updateLastObservationTimestamp(offset, timestampMs);
return true;
}

private void updateLastObservationTimestamp(final int offset, final long timestampMs)
{
// A cas loop to ensure that the timestamp is monotonic increasing.
for (; ; )
{
final long current = buffer.getLongVolatile(offset + LAST_OBSERVATION_TIMESTAMP_OFFSET);
if (current < timestampMs)
{
if (buffer.compareAndSetLong(offset + LAST_OBSERVATION_TIMESTAMP_OFFSET, current, timestampMs))
{
break;
}
}
else
{
break;
}
}
}

private static DistinctObservation find(
final DistinctObservation[] existingObservations, final Throwable observation)
final DistinctObservation[] existingObservations, final int startIndex, final Throwable observation)
{
DistinctObservation existingObservation = null;

for (final DistinctObservation o : existingObservations)
for (int k = startIndex; k < existingObservations.length; k++)
{
final DistinctObservation o = existingObservations[k];
if (equals(o.throwable, observation))
{
existingObservation = o;
Expand Down
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