Summary:
Providers observers with insight into ACKs received. Works for both client and server transport.
Attempts to prevent wasted memory by removing any allocated memory for ACK events if no packets in flight. In tandem, reduces allocs by _not_ removing allocated memory when packets are in flight (as this means more ACK events will occur soon...).
Reviewed By: jbeshay
Differential Revision: D31221280
fbshipit-source-id: 64b73aa74c757ebbfc27bb9c2a047d08dc7a77ca
Summary:
Currently the `packetsWritten` observer event is only triggered when ACK-eliciting packets are written to the network. This change makes it so that the event is triggered even when non ACK-eliciting packets are written. In addition, this change increases the information provided in the observer event to reduce the processing that must be performed by observers.
More specifically, this diff makes the following changes:
- It creates two new structs — `WriteEvent` and `PacketsWrittenEvent` — and makes `PacketsWrittenEvent` and `AppLimitedEvent` inherit from `WriteEvent`, which contains the base set of fields that appear in both derived events. The base set of fields includes `writeCount` and the reference to the list of `OutstandingPackets`.
- A `PacketsWrittenEvent` is generated after each write loop during which packets are written.
- The `PacketsWrittenEvent` records the total number of packets written (the sum of ACK-eliciting and non ACK-eliciting packets written) and the total number of ACK-eliciting packets written during the last loop. By exposing this information, observers can determine whether there is value in inspecting the list of `OutstandingPackets` before doing so.
- In the future, I'll extend this event to also report the number of stream bytes written.
- It adopts a new builder pattern for observer events to make it easier to create instances of these structures:
- We use this approach instead of aggregate initialization (specifically designated initializers via aggregate initialization), because designated initializers (C++20 feature, although supported by some compilers long before) is not yet supported on all platforms for which we need this code to compile.
- I intend to change the other observer events to use this pattern as the number of arguments in some of their constructors makes them increasingly difficult to deal with.
Reviewed By: mjoras
Differential Revision: D31216724
fbshipit-source-id: 42ceb922d46ab0e0dc356f8726c2d0467a219587
