Do seastar::connected_socket really do not support 2 writes at once from single thread?

[kelbon]

seastar output streams comment says:

/// \note All methods must be called sequentially.  That is, no method
/// may be invoked before the previous method's returned future is
/// resolved.

This means, 2 out.write() futures at one time is.. Undefined behavior? Why didn't you just add queue then? How programmer supposed to write code using your socket?

I know no one socket with such intertface ever, even windows system socket supports writing 2 times from one thread

[xemul]

PR making the output_stream::write() fiber-safe is truly welcome, if that's your message