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171import Dispatch
import Foundation
import Noise
import NoiseSerde
import OSLog
fileprivate let logger = Logger(
subsystem: "io.defn.NoiseBackend",
category: "Backend"
)
/// Statistics reported by Backends.
public struct BackendStats: Sendable {
public let totalRequests: UInt64
public let totalWaitDuration: Duration
public let totalReadDuration: Duration
public let totalWriteDuration: Duration
}
/// Client implementation for an async Racket backend.
public final class Backend: @unchecked Sendable {
private let ip = Pipe() // in from Racket's perspective
private let op = Pipe() // out from Racket's perspective
private let mu = DispatchSemaphore(value: 1) // mu guards everything below here
private let out: OutputPort!
private var seq = UVarint(0)
fileprivate var pending = [UInt64: ResponseHandler]()
private var totalRequests = UInt64(0)
private var totalWaitDuration = Duration.zero
private var totalReadDuration = Duration.zero
private var totalWriteDuration = Duration.zero
public init(withZo zo: URL, andMod modname: String, andProc proc: String) {
out = FileHandleOutputPort(withHandle: ip.fileHandleForWriting)
let server = Thread {
self.serve(zo, modname, proc)
}
server.name = "Noise Backend (Server)"
server.qualityOfService = .userInitiated
server.start()
let reader = Thread {
self.read()
}
reader.name = "Noise Backend (Reader)"
reader.qualityOfService = .userInitiated
reader.start()
}
private func serve(_ zo: URL, _ modname: String, _ proc: String) {
logger.debug("\(#function): booting Racket")
let t0 = ContinuousClock.now
let r = Racket(execPath: zo.path)
let dt = ContinuousClock.now - t0
logger.debug("\(#function): took \(dt) to boot Racket")
r.bracket {
logger.debug("\(#function): loading backend")
let t0 = ContinuousClock.now
r.load(zo: zo)
let dt = ContinuousClock.now - t0
logger.debug("\(#function): took \(dt) to load backend")
let mod = Val.cons(Val.symbol("quote"), Val.cons(Val.symbol(modname), Val.null))
let ifd = Val.fixnum(Int(ip.fileHandleForReading.fileDescriptor))
let ofd = Val.fixnum(Int(op.fileHandleForWriting.fileDescriptor))
let serve = r.require(Val.symbol(proc), from: mod).unsafeCar()
serve.unsafeApply(Val.cons(ifd, Val.cons(ofd, Val.null)))
preconditionFailure("Racket server exited")
}
}
private func read() {
let inp = FileHandleInputPort(withHandle: op.fileHandleForReading)
var buf = Data(count: 8*1024) // will grow as needed
while true {
let id = UVarint.read(from: inp, using: &buf)
//logger.debug("\(RequestId(value: id)): reading response; bufsize: \(buf.count)b")
mu.wait()
guard let handler = pending[id] else {
logger.fault("\(RequestId(value: id)): future is gone")
mu.signal()
continue
}
mu.signal()
let readDuration = handler.handle(from: inp, using: &buf)
//logger.debug("\(RequestId(value: id)): took \(Duration(nanos: readDuration), privacy: .public) to read")
mu.wait()
pending.removeValue(forKey: id)
let requestDuration = ContinuousClock.now - handler.time
totalRequests += 1
totalWaitDuration += requestDuration
totalReadDuration += readDuration
mu.signal()
logger.debug("\(RequestId(value: id)): took \(requestDuration) to fulfill")
}
}
public func send<T>(
writeProc write: (OutputPort) -> Void,
readProc read: @escaping (InputPort, inout Data) -> T,
commandName: String = #function
) -> Future<String, T> {
mu.wait()
let id = seq
seq += 1
logger.debug("\(RequestId(value: id)): \(commandName)")
let t0 = ContinuousClock.now
id.write(to: out)
write(out)
out.flush()
let dt = ContinuousClock.now - t0
let fut = Future<String, T>()
let handler = ResponseHandlerImpl<T>(id: id, fut: fut, read: read)
pending[id] = handler
totalWriteDuration += dt
mu.signal()
return fut
}
public func stats() -> BackendStats {
mu.wait()
defer { mu.signal() }
return BackendStats(
totalRequests: totalRequests,
totalWaitDuration: totalWaitDuration,
totalReadDuration: totalReadDuration,
totalWriteDuration: totalWriteDuration
)
}
}
fileprivate struct Request<Data: Writable>: Writable {
let id: UVarint
let data: Data
func write(to out: OutputPort) {
id.write(to: out)
data.write(to: out)
}
}
fileprivate protocol ResponseHandler {
var time: ContinuousClock.Instant { get }
func handle(from inp: InputPort, using buf: inout Data) -> Duration
}
fileprivate struct ResponseHandlerImpl<T>: ResponseHandler where T: Sendable {
let id: UInt64
let fut: Future<String, T>
let read: (InputPort, inout Data) -> T
let time = ContinuousClock.now
func handle(from inp: InputPort, using buf: inout Data) -> Duration {
let t0 = ContinuousClock.now
if inp.readByte() == 1 {
fut.resolve(with: read(inp, &buf))
} else {
fut.reject(with: String.read(from: inp, using: &buf))
}
return ContinuousClock.now - t0
}
}
fileprivate struct RequestId: CustomStringConvertible {
let value: UInt64
var description: String {
return String(format: "#%06d", value)
}
}