Allow AsyncWrapper to flush in batches instead of one giant flush

Have an application that writes several GByte data using NLog as part of startup-rutine.

After startup-rutine has completed, and just about to go online, then it performs a blocking garbage collection.

It could be nice if one could flush NLog buffers before starting the garbage collection. The problem is that the async-target might have a lot of data pending at this point.

If one calls NLog LogManager.Flush() then it will take the entire async-queue-buffer and write in one operation.

Lets say 200.000 items are still pending and each of them is 1000 bytes. Then it becomes close to 2 gigabyte which is the upper limit for a MemoryStream. Calling NLog LogManager.Flush() will then either lead to application crashing with out-of-memory exception, or discarding data because of stream-is-too-long.

It could be nice if AsyncWrapper had a MaxBatchSize (nullable) that could be configured instead of BatchSize. And it would also have effect during flush-operations. Instead of writing 200.000 in one operation, then it would do 200 write-operations of MaxBatchSize=1000

Start by locating AsyncWrapper and the LogManager.Flush() path, then trace how pending queue items are passed to the target during a flush. Verify the behavior with a large pending queue and confirm that a configured maximum batch size limits each flush operation without discarding data.