CODEWITHSUNDEEP
asynchronousbufferwinsocksendiocp
Megatron
Megatron

Reputation: 133

Winsock asynchronous multiple WSASend with one single buffer

MSDN states "For a Winsock application, once the WSASend function is called, the system owns these buffers and the application may not access them."

In a server application, does that mean that if I want to broadcast a message to multiple clients I cannot use a single buffer that holds the data and invoke WSASend on each socket with that one buffer?

Upvotes: 3

Views: 604

Answers (1)

Len Holgate
Len Holgate

Reputation: 21616

I don't have a documentation reference that confirms this is possible but I've been doing it for years and it hasn't failed yet, YMMV.

You CAN use a single data buffer as long as you have a unique OVERLAPPED structure per send. Since the WSABUF array is duplicated by the WSASend() call and can be stack based I would expect that you COULD have a single WSABUF array, but I've never done that.

What you DO need to make sure that you keep that single data buffer "alive" until all of the data writes complete.

Broadcasting like this can complicate a design if you tend to structure your extended OVERLAPPED so that it includes the data buffer, but it does avoid memory allocation and memory copying.

Note: I have a system whereby my extended OVERLAPPED structures include the data buffer and operation code and these are reference counted and pool and used for sends and recvs. When broadcasting a buffer I use a separate "buffer handle" per send, this handle is just an OVERLAPPED structure extended in a different way, it holds a reference to the original data buffer and has its own reference count. When all of the broadcast sends have completed all of the buffer handles will have been released and these will, in turn, have released the underlying data buffer for reuse.

Upvotes: 5

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