Swift implementation that uses only Swift's Grand Central Dispatch framework.
Before the introduction of async/await, this was the recommended way of doing concurrency in Swift,
and is still the only option for running Swift on Linux, Windows or MacOS 10.14 or earlier.
Swift's HTTP/concurrency model seems to rely on file descriptors under the hood, in order for scenario 3 to succeed, the file descriptors limit must be increased:
ulimit -n 10000
Run the tests (manages scenario server in Docker):
swift test -c release
Run against a manually started scenario server:
swift run -c release