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We're currently trying to fix an elsuive crash bug which didn't make much sense
to us until recently. Basically, our weapons access data from a singleton
"NDGameSettings" entity that is networked to all clients (in similar fashion to
how CTeam is broadcast to all clients). This singleton is currently accessed
from the weapon entity's Spawn() method on both client and server side.The
strange thing is, occasionnaly, the game would crash with an error-trapping
message saying that the NDGameSettings singleton instance pointer is null,
while the game has been running fine for several minutes. The only way of this
happening is if the weapon entity is created & spawned before the
NDGameSettings() entity. One would expect this error scenario to happen at map
load time since this is the only place where the NDGameSettings entity is
created. However, it doesnt crash at load time, but randomly during the game,
at any moment.Here is a quick snippet of the NDGameSettings code
used.*************************************************************class
CNDGameSettings : public CBaseEntity{ DECLARE_CLASS( CNDGameSettings,
CBaseEntity ); DECLARE_NETWORKCLASS();public: static CNDGameSettings*
GetInstance() { return s_pInstance; }protected: static CNDGameSettings*
s_pInstance; ...}CNDGameSettings::CNDGameSettings(){ if( GetInstance() )
{#ifdef CLIENT_DLL Warning("[CLIENT]
CNDGameSettings::CNDGameSettings() - An instance of CNDGameSettings already
exists on the client side\n");#else Warning("[SERVER]
CNDGameSettings::CNDGameSettings() - An instance of CNDGameSettings already
exists\n"); UTIL_Remove( GetInstance() );#endif } // Save pointer
to instance in class global s_pInstance =
this;}CNDGameSettings::~CNDGameSettings(){ if( GetInstance() == this ) {
Msg( "####### CNDGameSettings Destructor - Instance removed ########\n"
); s_pInstance = NULL; }}*** server side only ***int
CNDGameSettings::UpdateTransmitState( void ){ // always transmit to all
clients return SetTransmitState( FL_EDICT_ALWAYS
);}***************************************************************************After
several attempts at reproducing the crash bug, we found out that people with
bad/unstable connections and high latency were a lot more susceptible to this
crash. We therefore suspected that the bug had something to do with the network
behavior of HL2, and that some mechanism unknown to us would cause the
NDGameSettings entity to be recreated during the game, instead of just once at
map load time. Our debugging tests proved this, as we got the "#######
CNDGameSettings Destructor - Instance removed ########" message several times
during the game (along with many other debugging messages displayed when weapon
entities are created), using a laptop with a very bad connection to our test
server. Now my theory is this has something to do with this "full world
snapshot" update explained in the Source Multiplayer Networking article
(http://developer.valvesoftware.com/wiki/Source_Multiplayer_Networking):"Game
data is compressed using delta compression to reduce
network load. That means the server doesn't send a full world snapshot
each time, but rather only changes (a delta snapshot) that happened
since the last acknowledged update. With each packet sent between the
client and server, acknowledge numbers are attached to keep track of
their data flow. Usually full (non-delta) snapshots are only sent when
a game starts or a client suffers from heavy packet loss for a couple
of seconds. Clients can request a full snapshot manually with the cl_fullupdate
command."To me, it seems that the client-side entities list is cleared and
recreated when receiving a full world snapshot from the network. This would
explain why the client-side NDGameSettings entity is destroyed and then
recreated at random moments during the game and would also explain why the
"load time error scenario" can happen at anytime while the game is running,
especially to people with bad connections to the server.My questions:- Am I
looking in the wrong direction?- If not, could someone explain the mechanics
behind the full world snapshot a bit more indepth? - Are there any flags I can
set to my NDGameSettings entity to somehow make it resistant to this?- Why use
a proxy entity to network the GameRules data and not make the GameRules class
directly inherit from CBaseEntity? - What is a correct way of safely
creating/accessing singleton entity objects in Source?Thanks in advance!
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