Performant ways of emulating C's VARARGS using P/Invoke or unsafe C#
Provides two sample implementations for passing varidic arguments from C# to native (C).
Both implementations will pin pointer types (byte[] and string) for the duration of the native call. The unsafe implementation runs faster only because it can use stackalloc and avoiding to copy the VarArg structure that the safe version uses.
3205 calls/millisecond for SAFE "OnlyValueTypes"
4918 calls/millisecond for UNSAFE "OnlyValueTypes"
2209 calls/millisecond for SAFE "OnlyValueTypesAndString"
2952 calls/millisecond for UNSAFE "OnlyValueTypesAndString"
1617 calls/millisecond for SAFE "AllTypes"
1944 calls/millisecond for UNSAFE "AllTypes"
An interesting note here is that in some cases, pinning strings and buffers isn't the most performant way of passing these values. In the case of a slow native call, pinning objects will degrade GC performance and may cause erratic performance in multithreaded applications. In these situations, it's better to rely on P/Invoke or to use unmanaged memory allocations and make copies.