[proposal] NetlinkSocketBase to become thread unsafe

[svinota]

Current status and problem desciption

• methods like get(), put(), nlm_request() are thread safe
• all the received messages are parsed and buffered, regardless the sequence_number
• one thread acts as a master while running get(), it fetches data buffers with recv(); other threads are waiting for the buffer updates or until the master thread finishes running get()
• Marshal class allows mixed sequence_number values within one data buffer
• Marshal class allows terminator messages to be in the middle of on data buffer

Such complicated workflow makes any performance optimizations or local code refactoring next to impossible.

Proposal

• split out all the thread safe methods into one base class
• create another base class with same methods but thread unsafe
• configure base classes for NetlinkSocket on the fly or at the start time

Thread unsafe version features

• Drop any messages with alien sequence_number
• Assume that one buffer must have the same sequence_number
• The terminator message is always the last in the buffer

Discussion needed

Whether to make the thread unsafe version the default (starting from 0.8).

Related

• nlsocket: thread unsafe base #1012