Segfault on SteamGameServerNetworkingSockets.SendMessages

[IvMisticos]

When calling SteamGameServerNetworkingSockets.SendMessages the Segmentation fault occurs in the following code:

// Fields
byte[] Data;
HSteamNetConnection Connection;
int SendFlags;

void Send() {
// The send method
var message = Marshal.PtrToStructure<SteamNetworkingMessage_t>(SteamGameServerNetworkingUtils.AllocateMessage(Data.Length));

message.m_conn = Connection;
message.m_nFlags = SendFlags;

Marshal.Copy(Data, 0, message.m_pData, Data.Length);

var messages = new[] {message};

var messagesr = new long[messages.Length]; // Just so that it exists, idk what to do with it
SteamGameServerNetworkingSockets.SendMessages(messages.Length, messages, messagesr);
}

What could go wrong, what am I doing wrong? Same happens when I use SteamGameServerNetworkingSockets.SendMessageToConnection.

[IvMisticos]

Is this an issue with my C# code, or I misunderstand the Steamworks documentation, or an issue with Steamworks itself?

[yaakov-h]

I suspect it is both, this looks extremely tricky.

The immediate point of suspicion is that PtrToStructure does not map that memory to a .NET struct, but copies it.

Then, and I might be reading the method signatures wrong here, but SendMessages appears to want a pointer to a set of pointers, but Steamworks.NET is instead passing it a pointer (marshalled array) to a set of structs.

It also looks like you're not setting some of the fields on SteamNetworkingMessage_t - such as the function to free the data, which looks particularly sus.

Lastly, since the data is not pinned or in any way retained for the native Steamworks components, the .NET memory manager is free to move the data around in memory and garbage-collect it while Steam is still trying to use it, which is bound to crash eventually.

[IvMisticos]

The free function is managed by Steamworks itself if I specify amount of bytes in SteamGameServerNetworkingUtils.AllocateMessage() method arguments, pretty sure I don't have to unless I specify 0 or such.

[IvMisticos]

I'm copying the data to the buffer Steam allocated and does manage and will free on its own with Marshal.Copy (at least that's what I think it should do), means .NET should not free the data that is.. not even managed, it's Steamworks allocated memory, unmanaged. I just copy my data to a pointer Steamworks gives me.

[IvMisticos]

But PtrToStructure might be why, I'll look into it. What should I use instead? Just casting the pointer to the needed type?

That clearly didn't work, lol Cannot declare a pointer to a managed type 'Steamworks.SteamNetworkingMessage_t'

[IvMisticos]

@rlabrecque and I do agree that it looks weird that the Steamworks documentation requires pointers, but we are passing an array of structs.

[yaakov-h]

I’m not sure if your game engine supports it or not, but Unsafe.AsRef is probably more correct here than PtrToStructure. Unless you want to copy it back with StructureToPtr?

[IvMisticos]

Alright, used Unsafe.AsRef, but don't think it helped still. Might consider passing array of pointers with custom Steamworks.NET build to see if it works.

[rlabrecque]

#411

This may help you, I can't quite take a look at this deeper yet though

[IvMisticos]

So far NOT calling message.Release helped us move a bit further, still testing.

[rlabrecque]

Hmm can you check this one out too: #388

[IvMisticos]

This is due to Release indeed. Can we have it fixed so that it passes what it actually should, or make it accept an argument?

[IvMisticos]

Also please expose m_pfnFreeData since it's supposed to be settable by users, unless you're willing to make a pooling and stuff helper.