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[Java] Add method to get the latest value from the BroadcastReceiver #282

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[Java] Add method to get the latest value from the BroadcastReceiver #282

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29 changes: 27 additions & 2 deletions agrona/src/main/java/org/agrona/concurrent/broadcast/BroadcastReceiver.java
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Original file line number Diff line number Diff line change
Expand Up @@ -145,6 +145,24 @@ public MutableDirectBuffer buffer()
* set for the next message to be consumed. If no transmission is available then false.
*/
public boolean receiveNext()
{
return doReceiveNext(false);
}

/**
* Similar to {@link #receiveNext()}, but will skip all messages in the transmission stream
* and only set for the latest messaged.
*
* @return true if transmission is available with {@link #offset()}, {@link #length()} and {@link #typeId()}
* set for the next latest message to be consumed. If no transmission is available then false.
*/
public boolean receiveLatest()
{
return doReceiveNext(true);
}


private boolean doReceiveNext(final boolean latest)
{
boolean isAvailable = false;
final AtomicBuffer buffer = this.buffer;
Expand All @@ -154,16 +172,23 @@ public boolean receiveNext()
if (tail > cursor)
{
final int capacity = this.capacity;
int recordOffset = (int)cursor & (capacity - 1);

if (!validate(cursor, buffer, capacity))
{
lappedCount.lazySet(lappedCount.get() + 1);
if (!latest)
{
cursor = buffer.getLongVolatile(latestCounterIndex);
}
}

if (latest)
{
cursor = buffer.getLongVolatile(latestCounterIndex);
recordOffset = (int)cursor & (capacity - 1);
}

int recordOffset = (int)cursor & (capacity - 1);

this.cursor = cursor;
nextRecord = cursor + align(buffer.getInt(lengthOffset(recordOffset)), RECORD_ALIGNMENT);

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31 changes: 31 additions & 0 deletions agrona/src/test/java/org/agrona/concurrent/broadcast/BroadcastReceiverTest.java
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Original file line number Diff line number Diff line change
Expand Up @@ -151,6 +151,37 @@ void shouldReceiveTwoMessagesFromBuffer()
inOrder.verify(buffer).getLongVolatile(TAIL_INTENT_COUNTER_OFFSET);
}

@Test
void shouldReceiveLatestSecondMessagesFromBuffer()
{
final int length = 8;
final int recordLength = length + HEADER_LENGTH;
final int recordLengthAligned = align(recordLength, RECORD_ALIGNMENT);
final long tail = recordLengthAligned * 2L;
final long latestRecord = tail - recordLengthAligned;
final int recordOffsetTwo = (int)latestRecord;

when(buffer.getLongVolatile(TAIL_INTENT_COUNTER_OFFSET)).thenReturn(tail);
when(buffer.getLongVolatile(TAIL_COUNTER_INDEX)).thenReturn(tail);

when(buffer.getInt(lengthOffset(recordOffsetTwo))).thenReturn(recordLength);
when(buffer.getInt(typeOffset(recordOffsetTwo))).thenReturn(MSG_TYPE_ID);
when(buffer.getLongVolatile(TAIL_COUNTER_INDEX + length)).thenReturn(2L * length);

assertTrue(broadcastReceiver.receiveLatest());
assertThat(broadcastReceiver.typeId(), is(MSG_TYPE_ID));
assertThat(broadcastReceiver.buffer(), is(buffer));
assertThat(broadcastReceiver.offset(), is(msgOffset(recordOffsetTwo)));
assertThat(broadcastReceiver.length(), is(length));

assertTrue(broadcastReceiver.validate());

final InOrder inOrder = inOrder(buffer);
inOrder.verify(buffer).getLongVolatile(TAIL_COUNTER_INDEX);
inOrder.verify(buffer).getLongVolatile(TAIL_INTENT_COUNTER_OFFSET);
inOrder.verify(buffer).getLongVolatile(TAIL_INTENT_COUNTER_OFFSET);
}

@Test
void shouldLateJoinTransmission()
{
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