use a ring buffer for the datagram queue

[marten-seemann]

No description provided.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (1fce81f) 83.97% compared to head (60db14b) 83.99%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4223      +/-   ##
==========================================
+ Coverage   83.97%   83.99%   +0.02%     
==========================================
  Files         149      149              
  Lines       15419    15421       +2     
==========================================
+ Hits        12948    12952       +4     
+ Misses       1972     1971       -1     
+ Partials      499      498       -1     

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[sukunrt]

Sorry for the drive by comment. Just to point it out in case it was actually missed. Please ignore if not relevant.

Is a Peek followed by a Pop threadsafe considering that we only synchronise the calls individually and not the whole Peek + Pop operation?
I can't see any issues currently because it seems to be called only from the connection run loop go routine.

[marten-seemann]

Sorry for the drive by comment.

Thanks for reviewing!

Is a Peek followed by a Pop threadsafe considering that we only synchronise the calls individually and not the whole Peek + Pop operation?

The entire RingBuffer is not thread-safe (it doesn't try to: it doesn't even contain a mutex). It's the caller's responsibility to synchronize access.

I believe the datagramQueue does that: Peek will return a non-nil frame iff there's actually a frame queued. While it's possible that new frames are added between the Peek and Pop call, the only way that frame could disappear via Pop call, there's no other way to dequeue / delete a frame from the queue. Do you see any problem with that logic?

[sukunrt]

This makes sense.
Only Add happens from a different goroutine. Peek and Pop happen from the same goroutine so we will always Pop the element we received from Peek since Add puts it at the back of the queue.