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Do not fixup "out of order" messages from different lanes.

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Messages numbers cannot be compared across lanes, there are no ordering
guarantees, and actual arrival/decode order is actually the
preferred/expected result.  The previous code was making reorderings to
get message numbers from different lanes to be ascending.  This was legal,
but unexpected and undesirable.  It broke a unit test consistently on MacOS.

Added some comments to explain the situation more clearly

P4:10589992
This commit is contained in:
Fletcher Dunn
2026-04-12 18:18:05 -07:00
parent f14ea8a666
commit 99ae2827d9
1 changed files with 52 additions and 20 deletions
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src/steamnetworkingsockets/clientlib/steamnetworkingsockets_connections.cpp
+52 -20
View File
@@ -2742,25 +2742,60 @@ bool CSteamNetworkConnectionBase::ReceivedMessage( CSteamNetworkingMessage *pMsg
}
// Check for messages are received out of order. If the messages with a higher
// message number have not been removed from the queue, then we can correct this
const int64 nMessageNumber = pMsg->m_nMessageNumber;
if ( m_queueRecvMessages.m_pLast && unlikely( m_queueRecvMessages.m_pLast->m_nMessageNumber > pMsg->m_nMessageNumber ) )
// message number have not been removed from the queue, then we can correct this.
//
// NOTE: This is a totally optional fixup to try to reduce how often we present
// out-of-order messages to the application. Some applications don't
// handle out of order messages well. (I.e. they just drop them.) If we can
// correct it at this layer, without violating any of the guarantees of
// the protocol, it will improve the experience for applications with less
// robust code, at very little cost.
CSteamNetworkingMessage *pMsgInsertBefore = m_queueRecvMessages.m_pLast;
if ( pMsgInsertBefore )
{
const uint16 idxLane = pMsg->m_idxLane;
#if STEAMNETWORKINGSOCKETS_MAX_LANES > 1
if ( m_receiverState.m_vecLanes.size() > 1 )
{
// Scan backwards until we find the first message
// with a different lane number
while ( pMsgInsertBefore->m_idxLane != idxLane )
{
pMsgInsertBefore = pMsgInsertBefore->m_links.m_pPrev;
if ( !pMsgInsertBefore )
goto add_to_tail;
}
}
#endif
const int64 nMessageNumber = pMsg->m_nMessageNumber;
if ( likely( pMsgInsertBefore->m_nMessageNumber <= nMessageNumber ) )
goto add_to_tail;
// Scan the linked list to find the insertion point
int nMessagesGreaterThanCurrent = 1;
CSteamNetworkingMessage *pMsgInsertBefore = m_queueRecvMessages.m_pLast;
const int64 nMessageNumberLast = pMsgInsertBefore->m_nMessageNumber;
CSteamNetworkingMessage *ptr = pMsgInsertBefore;
for (;;)
{
Assert( pMsgInsertBefore->m_links.m_pQueue == &m_queueRecvMessages );
CSteamNetworkingMessage *pPrev = pMsgInsertBefore->m_links.m_pPrev;
if ( !pPrev || pPrev->m_nMessageNumber <= nMessageNumber )
Assert( ptr->m_links.m_pQueue == &m_queueRecvMessages );
CSteamNetworkingMessage *pPrev = ptr->m_links.m_pPrev;
if ( !pPrev )
break;
pMsgInsertBefore = pPrev;
++nMessagesGreaterThanCurrent;
if ( pPrev->m_idxLane == idxLane )
{
if ( pPrev->m_nMessageNumber <= nMessageNumber )
break;
pMsgInsertBefore = ptr;
++nMessagesGreaterThanCurrent;
}
ptr = pPrev;
}
const int64 nMessageNumberInsertBefore = pMsgInsertBefore->m_nMessageNumber;
// Insert before this in the main queue for the connection
@@ -2797,21 +2832,18 @@ bool CSteamNetworkConnectionBase::ReceivedMessage( CSteamNetworkingMessage *pMsg
(long long)nMessageNumberInsertBefore,
(long long)nMessageNumberLast );
return true;
}
else
{
add_to_tail:
// Add to end of my queue.
pMsg->LinkToQueueTail( &CSteamNetworkingMessage::m_links, &m_queueRecvMessages );
// Add to end of my queue.
pMsg->LinkToQueueTail( &CSteamNetworkingMessage::m_links, &m_queueRecvMessages );
// Add to the poll group, if we are in one
if ( m_pPollGroup )
pMsg->LinkToQueueTail( &CSteamNetworkingMessage::m_linksSecondaryQueue, &m_pPollGroup->m_queueRecvMessages );
// Each if() branch has its own unlock, so we can spew in the branch above
g_lockAllRecvMessageQueues.unlock();
}
// Add to the poll group, if we are in one
if ( m_pPollGroup )
pMsg->LinkToQueueTail( &CSteamNetworkingMessage::m_linksSecondaryQueue, &m_pPollGroup->m_queueRecvMessages );
g_lockAllRecvMessageQueues.unlock();
return true;
}