Venice provides CSP for Swift 2.2.
- No
Foundationdependency (Linux ready) - Coroutines
- Coroutine Preallocation
- Channels
- Fallible Channels
- Receive-only Channels
- Send-only Channels
- Channel Iteration
- Select
- Timers
- Tickers
- File Descriptor Polling
- IP
- TCP Sockets
- UDP Sockets
- UNIX Sockets
- File
Venice wraps a fork of the C library libmill.
Venice is the base for:
- Epoch - HTTP server
##Usage
func doSomething() {
print("did something")
}
// call sync
doSomething()
// call async
co(doSomething())
// async closure
co {
print("did something else")
}co {
// wakes up 1 second from now
wakeUp(now + 1 * second)
print("yawn")
}
// nap for two seconds so the program
// doesn't terminate before the print
nap(2 * second)after runs the coroutine after the specified duration.
after(1 * second) {
print("yoo")
}
// same as
co {
nap(1 * second)
print("yoo")
}Channels are typed and return optionals wrapping the value or nil if the channel is closed and doesn't have any values left in the buffer.
let messages = Channel<String>()
co(messages <- "ping")
let message = <-messages
print(message!)
// without operators
let messages = Channel<String>()
co(messages.receive("ping"))
let message = messages.send()
print(message!)
// buffered channels
let messages = Channel<String>(bufferSize: 2)
messages <- "buffered"
messages <- "channel"
print(!<-messages)
print(!<-messages)You can get a reference to a channel with receive or send only capabilities.
func receiveOnly(channel: ReceivingChannel<String>) {
// can only receive
channel <- "yo"
}
func sendOnly(channel: SendingChannel<String>) {
// can only send
<-channel
}
let channel = Channel<String>(bufferSize: 1)
receiveOnly(channel.receivingChannel)
sendOnly(channel.sendingChannel)Fallible channels accept values and errors as well.
struct Error : ErrorType {}
let channel = FallibleChannel<String>(bufferSize: 2)
channel <- "yo"
channel <- Error()
do {
let yo = try <-channel
try <-channel // will throw
} catch {
print("error")
}Sometimes select can clash with the system libraries function with the same name select. To solve this you can call Venice's select with Venice.selector with the terser alias sel.
let channel = Channel<String>()
let fallibleChannel = FallibleChannel<String>()
select { when in
when.receiveFrom(channel) { value in
print("received \(value)")
}
when.receiveFrom(fallibleChannel) { result in
result.success { value in
print(value)
}
result.failure { error in
print(error)
}
}
when.send("value", to: channel) {
print("sent value")
}
when.send("value", to: fallibleChannel) {
print("sent value")
}
when.throwError(Error(), into: fallibleChannel) {
print("threw error")
}
when.timeout(now + 1 * second) {
print("timeout")
}
when.otherwise {
print("default case")
}
}You can disable a channel selection by turning it to nil
var channelA: Channel<String>? = Channel<String>()
var channelB: Channel<String>? = Channel<String>()
if arc4random_uniform(2) == 0 {
channelA = nil
print("disabled channel a")
} else {
channelB = nil
print("disabled channel b")
}
co { channelA?.receive("a") }
co { channelB?.receive("b") }
sel { when in
when.receiveFrom(channelA) { value in
print("received \(value) from channel a")
}
when.receiveFrom(channelB) { value in
print("received \(value) from channel b")
}
}Another way to disable a channel selection is to simply put it's case inside an if.
let channelA = Channel<String>()
let channelB = Channel<String>()
co(channelA <- "a")
co(channelB <- "b")
select { when in
if arc4random_uniform(2) == 0 {
print("disabled channel b")
when.receiveFrom(channelA) { value in
print("received \(value) from channel a")
}
} else {
print("disabled channel a")
when.receiveFrom(channelB) { value in
print("received \(value) from channel b")
}
}
}A lot of times we need to wrap our select inside a while loop. To make it easier to work with this pattern we can use forSelect. forSelect will loop until you call done().
func flipCoin(result: FallibleChannel<String>) {
if arc4random_uniform(2) == 0 {
result <- "Success"
} else {
result <- Error(description: "Something went wrong")
}
}
let results = FallibleChannel<String>()
co(flipCoin(results))
forSelect { when, done in
when.receiveFrom(results) { result in
result.success { value in
print(value)
done()
}
result.failure { error in
print("\(error). Retrying...")
co(flipCoin(results))
}
}
}// local
do {
// all network interfaces
let ip1 = try IP(port: 5555, mode: .IPV4)
// specific network interface
let ip2 = try IP(networkInterface: "en0", port: 5555, mode: .IPV6)
} catch {
// something bad happened :(
}
// remote
do {
// if the deadline is reached the call will throw
let ip3 = try IP(address: "127.0.0.1", port: 5555, mode: .IPV4, deadline: now + 10 * second)
} catch {
// something bad happened :(
}// server
do {
let ip = try IP(port: 5555)
let serverSocket = try TCPServerSocket(ip: ip)
let clientSocket = try serverSocket.accept()
let yo = try clientSocket.receiveString(untilDelimiter: "\n")
} catch {
// something bad happened :(
}
// client
do {
let ip = try IP(address: "127.0.0.1", port: 5555)
let clientSocket = try TCPClientSocket(ip: ip)
let deadline = now + 10 * second
// calls to send append the data to an internal
// buffer to minimize system calls
try clientSocket.sendString("yo\n", deadline: deadline)
// flush actually sends all data in the buffer
try clientSocket.flush()
} catch {
// something bad happened :(
}- Install
libvenice
$ git clone https://github.com/Zewo/libvenice.git
$ cd libvenice
$ make
$ dpkg -i libvenice.deb- Add
Veniceto yourPackage.swift
import PackageDescription
let package = Package(
dependencies: [
.Package(url: "https://github.com/Zewo/Venice.git", majorVersion: 0, minor: 1)
]
)The examples 01-15 were taken from gobyexample and translated from Go to Swift using Venice.
A coroutine is a lightweight thread of execution.
func f(from: String) {
for i in 0 ..< 4 {
print("\(from): \(i)")
yield
}
}Suppose we have a function call f(s). Here's how we'd call
that in the usual way, running it synchronously.
f("direct")
To invoke this function in a coroutine, use co(f(s)). This new
coroutine will execute concurrently with the calling one.
co(f("coroutine"))
You can also start a coroutine with a closure.
co {
print("going")
}
Our two function calls are running asynchronously in separate coroutines now, so execution falls through to here. We wait 1 second before the program exits
nap(1 * second)
print("done")When we run this program, we see the output of the blocking call first, then the interleaved output of the two coroutines. This interleaving reflects the coroutines being run concurrently by the runtime.
###Output
direct: 0
direct: 1
direct: 2
direct: 3
coroutine: 0
going
coroutine: 1
coroutine: 2
coroutine: 3
done
Channels are the pipes that connect concurrent coroutines. You can send values into channels from one coroutine and receive those values into another coroutine.
Create a new channel with Channel<Type>().
Channels are typed by the values they convey.
let messages = Channel<String>()Send a value into a channel using the channel <- value
syntax. Here we send "ping" to the messages
channel we made above, from a new coroutine.
co(messages <- "ping")The <-channel syntax receives a value from the
channel. Here we'll receive the "ping" message
we sent above and print it out.
let message = <-messages
print(message!)When we run the program the "ping" message is successfully passed from one coroutine to another via our channel. By default sends and receives block until both the sender and receiver are ready. This property allowed us to wait at the end of our program for the "ping" message without having to use any other synchronization.
Values received from channels are Optionals. If you try to get a value from a closed channel with no values left in the buffer, it'll return nil. If you are sure that there is a value wraped in the Optional, you can use the !<- operator, which returns an implictly unwraped optional.
###Output
ping
By default channels are unbuffered, meaning that they
will only accept receiving values (channel <- value) if there is a
corresponding receive (let value = <-channel) ready to receive the
value sent by the channel. Buffered channels accept a limited
number of values without a corresponding receiver for
those values.
Here we make a channel of strings buffering up to 2 values.
let messages = Channel<String>(bufferSize: 2)Because this channel is buffered, we can send these values into the channel without a corresponding concurrent receive.
messages <- "buffered"
messages <- "channel"Later we can receive these two values as usual.
print(!<-messages)
print(!<-messages)###Output
buffered
channel
We can use channels to synchronize execution across coroutines. Here's an example of using a blocking receive to wait for a coroutine to finish.
This is the function we'll run in a coroutine. The
done channel will be used to notify another
coroutine that this function's work is done.
func worker(done: Channel<Bool>) {
print("working...")
nap(1 * second)
print("done")
done <- true // Send a value to notify that we're done.
}Start a worker coroutine, giving it the channel to notify on.
let done = Channel<Bool>(bufferSize: 1)
co(worker(done))Block until we receive a notification from the worker on the channel.
<-doneIf you removed the <-done line from this program, the program would
exit before the worker even started.
###Output
working...
done
When using channels as function parameters, you can specify if a channel is meant to only send or receive values. This specificity increases the type-safety of the program.
This ping function only accepts a channel that receives
values. It would be a compile-time error to try to
receive values from this channel.
func ping(pings: ReceivingChannel<String>, message: String) {
pings <- message
}The pong function accepts one channel that only sends values
(pings) and a second that only receives values (pongs).
func pong(pings: SendingChannel<String>, _ pongs: ReceivingChannel<String>) {
let message = !<-pings
pongs <- message
}
let pings = Channel<String>(bufferSize: 1)
let pongs = Channel<String>(bufferSize: 1)
ping(pings.receivingChannel, message: "passed message")
pong(pings.sendingChannel, pongs.receivingChannel)
print(!<-pongs)###Output
passed message
Select lets you wait on multiple channel operations. Combining coroutines and channels with select is an extremely powerful feature.
For our example we'll select across two channels.
let channel1 = Channel<String>()
let channel2 = Channel<String>()Each channel will receive a value after some amount of time, to simulate e.g. blocking RPC operations executing in concurrent coroutines.
co {
nap(1 * second)
channel1 <- "one"
}
co {
nap(2 * second)
channel2 <- "two"
}We'll use select to await both of these values
simultaneously, printing each one as it arrives.
for _ in 0 ..< 2 {
select { when in
when.receiveFrom(channel1) { message1 in
print("received \(message1)")
}
when.receiveFrom(channel2) { message2 in
print("received \(message2)")
}
}
}We receive the values "one" and then "two" as expected.
Note that the total execution time is only ~2 seconds since
both the 1 and 2 second naps execute concurrently.
###Output
received one
received two
Timeouts are important for programs that connect to
external resources or that otherwise need to bound
execution time. Implementing timeouts is easy and
elegant thanks to channels and select.
For our example, suppose we're executing an external
call that returns its result on a channel channel1
after 2s.
let channel1 = Channel<String>(bufferSize: 1)
co {
nap(2 * second)
channel1 <- "result 1"
}Here's the select implementing a timeout.
receiveFrom(channel1) awaits the result and timeout(now + 1 * second)
awaits a value to be sent after the timeout of
1s. Since select proceeds with the first
receive that's ready, we'll take the timeout case
if the operation takes more than the allowed 1s.
select { when in
when.receiveFrom(channel1) { result in
print(result)
}
when.timeout(now + 1 * second) {
print("timeout 1")
}
}If we allow a longer timeout of 3s, then the receive
from channel2 will succeed and we'll print the result.
let channel2 = Channel<String>(bufferSize: 1)
co {
nap(2 * second)
channel2 <- "result 2"
}
select { when in
when.receiveFrom(channel2) { result in
print(result)
}
when.timeout(now + 3 * second) {
print("timeout 2")
}
}Running this program shows the first operation timing out and the second succeeding.
Using this select timeout pattern requires communicating results over channels. This is a good idea in general because other important features are based on channels and select. We’ll look at two examples of this next: timers and tickers.
###Output
timeout 1
result 2
Basic sends and receives on channels are blocking.
However, we can use select with a otherwise clause to
implement non-blocking sends, receives, and even
non-blocking multi-way selects.
let messages = Channel<String>()
let signals = Channel<Bool>()Here's a non-blocking receive. If a value is
available on messages then select will take
the receiveFrom(messages) case with that value. If not
it will immediately take the otherwise case.
select { when in
when.receiveFrom(messages) { message in
print("received message \(message)")
}
when.otherwise {
print("no message received")
}
}A non-blocking send works similarly.
let message = "hi"
select { when in
when.send(message, to: messages) {
print("sent message \(message)")
}
when.otherwise {
print("no message sent")
}
}We can use multiple cases above the otherwise
clause to implement a multi-way non-blocking
select. Here we attempt non-blocking receives
on both messages and signals.
select { when in
when.receiveFrom(messages) { message in
print("received message \(message)")
}
when.receiveFrom(signals) { signal in
print("received signal \(signal)")
}
when.otherwise {
print("no activity")
}
}###Output
no message received
no message sent
no activity
Closing a channel indicates that no more values can be sent to it. This can be useful to communicate completion to the channel's receivers.
In this example we'll use a jobs channel to
communicate work to be done to a worker coroutine. When we have no more jobs for
the worker we'll close the jobs channel.
let jobs = Channel<Int>(bufferSize: 5)
let done = Channel<Bool>()Here's the worker coroutine. It repeatedly receives
from jobs with j = <-jobs. The return value
will be nil if jobs has been closed and all
values in the channel have already been received.
We use this to notify on done when we've worked
all our jobs.
co {
while true {
if let job = <-jobs {
print("received job \(job)")
} else {
print("received all jobs")
done <- true
return
}
}
}This sends 3 jobs to the worker over the jobs
channel, then closes it.
for job in 1 ... 3 {
print("sent job \(job)")
jobs <- job
}
jobs.close()
print("sent all jobs")We await the worker using the synchronization approach we saw earlier.
<-doneThe idea of closed channels leads naturally to our next example: iterating over channels.
###Output
sent job 1
received job 1
sent job 2
received job 2
sent job 3
received job 3
sent all jobs
received job 3
received all jobs
We can use for in to iterate over
values received from a channel.
We'll iterate over 2 values in the queue channel.
let queue = Channel<String>(bufferSize: 2)
queue <- "one"
queue <- "two"
queue.close()This for in loop iterates over each element as it's
received from queue. Because we closed the
channel above, the iteration terminates after
receiving the 2 elements. If we didn't close it
we'd block on a 3rd receive in the loop.
for element in queue {
print(element)
}This example also showed that it’s possible to close a non-empty channel but still have the remaining values be received.
###Output
one
two
We often want to execute code at some point in the future, or repeatedly at some interval. Timer and ticker features make both of these tasks easy. We'll look first at timers and then at tickers.
Timers represent a single event in the future. You tell the timer how long you want to wait, and it provides a channel that will be notified at that time. This timer will wait 2 seconds.
let timer1 = Timer(deadline: now + 2 * second)The <-timer1.channel blocks on the timer's channel
until it sends a value indicating that the timer
expired.
<-timer1.channel
print("Timer 1 expired")If you just wanted to wait, you could have used
nap. One reason a timer may be useful is
that you can cancel the timer before it expires.
Here's an example of that.
let timer2 = Timer(deadline: now + 1 * second)
co {
<-timer2.channel
print("Timer 2 expired")
}
let stop2 = timer2.stop()
if stop2 {
print("Timer 2 stopped")
}The first timer will expire ~2s after we start the program, but the second should be stopped before it has a chance to expire.
###Output
Timer 1 expired
Timer 2 stopped
Timers are for when you want to do something once in the future - tickers are for when you want to do something repeatedly at regular intervals. Here's an example of a ticker that ticks periodically until we stop it.
Tickers use a similar mechanism to timers: a
channel that is sent values. Here we'll use the
generator builtin on the channel to iterate over
the values as they arrive every 500ms.
let ticker = Ticker(period: 500 * millisecond)
co {
for time in ticker.channel {
print("Tick at \(time)")
}
}Tickers can be stopped like timers. Once a ticker is stopped it won't receive any more values on its channel. We'll stop ours after 1600ms.
nap(1600 * millisecond)
ticker.stop()
print("Ticker stopped")When we run this program the ticker should tick 3 times before we stop it.
###Output
Tick at 37024098
Tick at 37024599
Tick at 37025105
Ticker stopped
In this example we'll look at how to implement a worker pool using coroutines and channels.
Here's the worker, of which we'll run several
concurrent instances. These workers will receive
work on the jobs channel and send the corresponding
results on results. We'll sleep a second per job to
simulate an expensive task.
func worker(id: Int, jobs: Channel<Int>, results: Channel<Int>) {
for job in jobs {
print("worker \(id) processing job \(job)")
nap(1 * second)
results <- job * 2
}
}In order to use our pool of workers we need to send them work and collect their results. We make 2 channels for this.
let jobs = Channel<Int>(bufferSize: 100)
let results = Channel<Int>(bufferSize: 100)This starts up 3 workers, initially blocked because there are no jobs yet.
for workerId in 1 ... 3 {
co(worker(workerId, jobs: jobs, results: results))
}Here we send 9 jobs and then close that
channel to indicate that's all the work we have.
for job in 1 ... 9 {
jobs <- job
}
jobs.close()Finally we collect all the results of the work.
for _ in 1 ... 9 {
<-results
}Our running program shows the 9 jobs being executed by various workers. The program only takes about 3 seconds despite doing about 9 seconds of total work because there are 3 workers operating concurrently.
###Output
worker 1 processing job 1
worker 2 processing job 2
worker 3 processing job 3
worker 1 processing job 4
worker 2 processing job 5
worker 3 processing job 6
worker 1 processing job 7
worker 2 processing job 8
worker 3 processing job 9
Rate limiting is an important mechanism for controlling resource utilization and maintaining quality of service. Venice elegantly supports rate limiting with coroutines, channels, and tickers.
First we'll look at basic rate limiting. Suppose we want to limit our handling of incoming requests. We'll serve these requests off a channel of the same name.
var requests = Channel<Int>(bufferSize: 5)
for request in 1 ... 5 {
requests <- request
}
requests.close()This limiter channel will receive a value
every 200 milliseconds. This is the regulator in
our rate limiting scheme.
let limiter = Ticker(period: 200 * millisecond)By blocking on a receive from the limiter channel
before serving each request, we limit ourselves to
1 request every 200 milliseconds.
for request in requests {
<-limiter.channel
print("request \(request) \(now)")
}
print("")We may want to allow short bursts of requests in
our rate limiting scheme while preserving the
overall rate limit. We can accomplish this by
buffering our limiter channel. This burstyLimiter
channel will allow bursts of up to 3 events.
let burstyLimiter = Channel<Int64>(bufferSize: 3)Fill up the channel to represent allowed bursting.
for _ in 0 ..< 3 {
burstyLimiter <- now
}Every 200 milliseconds we'll try to add a new
value to burstyLimiter, up to its limit of 3.
co {
for time in Ticker(period: 200 * millisecond).channel {
burstyLimiter <- time
}
}Now simulate 5 more incoming requests. The first
3 of these will benefit from the burst capability
of burstyLimiter.
let burstyRequests = Channel<Int>(bufferSize: 5)
for request in 1 ... 5 {
burstyRequests <- request
}
burstyRequests.close()
for request in burstyRequests {
<-burstyLimiter
print("request \(request) \(now)")
}Running our program we see the first batch of requests handled once every ~200 milliseconds as desired.
For the second batch of requests we serve the first 3 immediately because of the burstable rate limiting, then serve the remaining 2 with ~200ms delays each.
###Output
request 1 37221046
request 2 37221251
request 3 37221453
request 4 37221658
request 5 37221860
request 1 37221863
request 2 37221864
request 3 37221865
request 4 37222064
request 5 37222265
In this example our state will be owned by a single
coroutine. This will guarantee that the data is never
corrupted with concurrent access. In order to read or
write that state, other coroutines will send messages
to the owning coroutine and receive corresponding
replies. These ReadOperation and WriteOperation structs
encapsulate those requests and a way for the owning
coroutine to respond.
struct ReadOperation {
let key: Int
let responses: Channel<Int>
}
struct WriteOperation {
let key: Int
let value: Int
let responses: Channel<Bool>
}We'll count how many operations we perform.
var operations = 0The reads and writes channels will be used by
other coroutines to issue read and write requests,
respectively.
let reads = Channel<ReadOperation>()
let writes = Channel<WriteOperation>()Here is the coroutine that owns the state, which
is a dictionary private
to the stateful coroutine. This coroutine repeatedly
selects on the reads and writes channels,
responding to requests as they arrive. A response
is executed by first performing the requested
operation and then sending a value on the response
channel responses to indicate success (and the desired
value in the case of reads).
co {
var state: [Int: Int] = [:]
while true {
select { when in
when.receiveFrom(reads) { read in
read.responses <- state[read.key] ?? 0
}
when.receiveFrom(writes) { write in
state[write.key] = write.value
write.responses <- true
}
}
}
}This starts 100 coroutines to issue reads to the
state-owning coroutine via the reads channel.
Each read requires constructing a ReadOperation, sending
it over the reads channel, and then receiving the
result over the provided responses channel.
for _ in 0 ..< 100 {
co {
while true {
let read = ReadOperation(
key: Int(arc4random_uniform(5)),
responses: Channel<Int>()
)
reads <- read
<-read.responses
operations++
}
}
}We start 10 writes as well, using a similar approach.
for _ in 0 ..< 10 {
co {
while true {
let write = WriteOperation(
key: Int(arc4random_uniform(5)),
value: Int(arc4random_uniform(100)),
responses: Channel<Bool>()
)
writes <- write
<-write.responses
operations++
}
}
}Let the coroutines work for a second.
nap(1 * second)Finally, capture and report the operations count.
print("operations: \(operations)")###Output
operations: 55798
func whisper(left: ReceivingChannel<Int>, _ right: SendingChannel<Int>) {
left <- 1 + !<-right
}
let n = 1000
let leftmost = Channel<Int>()
var right = leftmost
var left = leftmost
for _ in 0 ..< n {
right = Channel<Int>()
co(whisper(left.receivingChannel, right.sendingChannel))
left = right
}
co {
right <- 1
}
print(!<-leftmost)###Output
1001
final class Ball { var hits: Int = 0 }
func player(name: String, table: Channel<Ball>) {
while true {
let ball = !<-table
ball.hits++
print("\(name) \(ball.hits)")
nap(100 * millisecond)
table <- ball
}
}
let table = Channel<Ball>()
co(player("ping", table: table))
co(player("pong", table: table))
table <- Ball()
nap(1 * second)
<-table###Output
ping 1
pong 2
ping 3
pong 4
ping 5
pong 6
ping 7
pong 8
ping 9
pong 10
ping 11
var channelA: Channel<String>? = Channel<String>()
var channelB: Channel<String>? = Channel<String>()
if arc4random_uniform(2) == 0 {
channelA = nil
print("disabled channel a")
} else {
channelB = nil
print("disabled channel b")
}
co { channelA?.receive("a") }
co { channelB?.receive("b") }
select { when in
when.receiveFrom(channelA) { value in
print("received \(value) from channel a")
}
when.receiveFrom(channelB) { value in
print("received \(value) from channel b")
}
}###Output
disabled channel b
received a from channel a
or
disabled channel a
received b from channel b
func fibonacci(n: Int, channel: Channel<Int>) {
var x = 0
var y = 1
for _ in 0 ..< n {
channel <- x
(x, y) = (y, x + y)
}
channel.close()
}
let fibonacciChannel = Channel<Int>(bufferSize: 10)
co(fibonacci(fibonacciChannel.bufferSize, channel: fibonacciChannel))
for n in fibonacciChannel {
print(n)
}###Output
0
1
1
2
3
5
8
13
21
34
let tick = Ticker(period: 100 * millisecond).channel
let boom = Timer(deadline: now + 500 * millisecond).channel
var done = false
while !done {
select { when in
when.receiveFrom(tick) { _ in
print("tick")
}
when.receiveFrom(boom) { _ in
print("BOOM!")
done = true
}
when.otherwise {
print(" .")
nap(50 * millisecond)
}
}
}###Output
.
.
tick
.
.
tick
.
.
tick
.
.
tick
.
BOOM!
func flipCoin(result: FallibleChannel<String>) {
struct Error : ErrorType, CustomStringConvertible { let description: String }
if arc4random_uniform(2) == 0 {
result <- "Success"
} else {
result <- Error(description: "Something went wrong.")
}
}
let results = FallibleChannel<String>()
var done = false
co(flipCoin(results))
while !done {
do {
let value = try !<-results
print(value)
done = true
} catch {
print("\(error) Retrying...")
co(flipCoin(results))
}
}###Output
Something went wrong. Retrying...
Something went wrong. Retrying...
Something went wrong. Retrying...
Something went wrong. Retrying...
Something went wrong. Retrying...
Success
struct Error : ErrorType, CustomStringConvertible { let description: String }
func flipCoin(result: FallibleChannel<String>) {
if arc4random_uniform(2) == 0 {
result <- "Success"
} else {
result <- Error(description: "Something went wrong")
}
}
let results = FallibleChannel<String>()
co(flipCoin(results))
select { when in
when.receiveFrom(results) { result in
result.success { value in
print(value)
}
result.failure { error in
print(error)
}
}
}###Output
Success
or
Something went wrong
extension CollectionType where Index == Int {
func shuffle() -> [Generator.Element] {
var list = Array(self)
list.shuffleInPlace()
return list
}
}
extension MutableCollectionType where Index == Int {
mutating func shuffleInPlace() {
if count < 2 { return }
for i in 0..<count - 1 {
let j = Int(arc4random_uniform(UInt32(count - i))) + i
guard i != j else { continue }
swap(&self[i], &self[j])
}
}
}
final class Tree<T> {
var left: Tree?
var value: T
var right: Tree?
init(left: Tree?, value: T, right: Tree?) {
self.left = left
self.value = value
self.right = right
}
}Traverses a tree depth-first, sending each Value on a channel.
func walk<T>(tree: Tree<T>?, channel: Channel<T>) {
if let tree = tree {
walk(tree.left, channel: channel)
channel <- tree.value
walk(tree.right, channel: channel)
}
}Launches a walk in a new coroutine, and returns a read-only channel of values.
func walker<T>(tree: Tree<T>?) -> SendingChannel<T> {
let channel = Channel<T>()
co {
walk(tree, channel: channel)
channel.close()
}
return channel.sendingChannel
}Reads values from two walkers that run simultaneously, and returns true if tree1 and tree2 have the same contents.
func ==<T : Equatable>(tree1: Tree<T>, tree2: Tree<T>) -> Bool {
let channel1 = walker(tree1)
let channel2 = walker(tree2)
while true {
let value1 = <-channel1
let value2 = <-channel2
if value1 == nil || value2 == nil {
return value1 == value2
}
if value1 != value2 {
break
}
}
return false
}Returns a new, random binary tree holding the values 1k, 2k, ..., n*k.
func newTree(n n: Int, k: Int) -> Tree<Int> {
var tree: Tree<Int>?
for value in (1...n).shuffle() {
tree = insert(tree, value: value * k)
}
return tree!
}Inserts a value in the tree
func insert(tree: Tree<Int>?, value: Int) -> Tree<Int> {
if let tree = tree {
if value < tree.value {
tree.left = insert(tree.left, value: value)
return tree
} else {
tree.right = insert(tree.right, value: value)
return tree
}
} else {
return Tree<Int>(left: nil, value: value, right: nil)
}
}
let tree = newTree(n: 100, k: 1)
print("Same contents \(tree == newTree(n: 100, k: 1))")
print("Differing sizes \(tree == newTree(n: 99, k: 1))")
print("Differing values \(tree == newTree(n: 100, k: 2))")
print("Dissimilar \(tree == newTree(n: 101, k: 2))")###Output
Same contents true
Differing sizes false
Differing values false
Dissimilar false
let channelA = Channel<String>()
let channelB = Channel<String>()
co(channelA <- "a")
co(channelB <- "b")
select { when in
if arc4random_uniform(2) == 0 {
print("disabled channel b")
when.receiveFrom(channelA) { value in
print("received \(value) from channel a")
}
} else {
print("disabled channel a")
when.receiveFrom(channelB) { value in
print("received \(value) from channel b")
}
}
}###Output
disabled channel b
received a from channel a
or
disabled channel a
received b from channel b
struct Item : Equatable {
let domain: String
let title: String
let GUID: String
}
func ==(lhs: Item, rhs: Item) -> Bool {
return lhs.GUID == rhs.GUID
}
struct FetchResponse {
let items: [Item]
let nextFetchTime: Int
}
protocol FetcherType {
func fetch() -> Result<FetchResponse>
}
struct Fetcher : FetcherType {
let domain: String
func randomItems() -> [Item] {
let items = [
Item(domain: domain, title: "Swift 2.0", GUID: "1"),
Item(domain: domain, title: "Strings in Swift 2", GUID: "2"),
Item(domain: domain, title: "Swift-er SDK", GUID: "3"),
Item(domain: domain, title: "Swift 2 Apps in the App Store", GUID: "4"),
Item(domain: domain, title: "Literals in Playgrounds", GUID: "5"),
Item(domain: domain, title: "Swift Open Source", GUID: "6")
]
return [Item](items[0..<Int(arc4random_uniform(UInt32(items.count)))])
}
func fetch() -> Result<FetchResponse> {
if arc4random_uniform(2) == 0 {
let fetchResponse = FetchResponse(
items: randomItems(),
nextFetchTime: now + 300 * millisecond
)
return Result.Value(fetchResponse)
} else {
struct Error : ErrorType, CustomStringConvertible { let description: String }
return Result.Error(Error(description: "Network Error"))
}
}
}
protocol SubscriptionType {
var updates: SendingChannel<Item> { get }
func close() -> ErrorType?
}
struct Subscription : SubscriptionType {
let fetcher: FetcherType
let items = Channel<Item>()
let closing = Channel<Channel<ErrorType?>>()
init(fetcher: FetcherType) {
self.fetcher = fetcher
co(self.getUpdates())
}
var updates: SendingChannel<Item> {
return self.items.sendingChannel
}
func getUpdates() {
let maxPendingItems = 10
let fetchDone = Channel<Result<FetchResponse>>(bufferSize: 1)
var lastError: ErrorType?
var pendingItems: [Item] = []
var seenItems: [Item] = []
var nextFetchTime = now
var fetching = false
forSelect { when, done in
when.receiveFrom(closing) { errorChannel in
errorChannel <- lastError
self.items.close()
done()
}
if !fetching && pendingItems.count < maxPendingItems {
when.timeout(nextFetchTime) {
fetching = true
co {
fetchDone <- self.fetcher.fetch()
}
}
}
when.receiveFrom(fetchDone) { fetchResult in
fetching = false
fetchResult.success { response in
for item in response.items {
if !seenItems.contains(item) {
pendingItems.append(item)
seenItems.append(item)
}
}
lastError = nil
nextFetchTime = response.nextFetchTime
}
fetchResult.failure { error in
lastError = error
nextFetchTime = now + 1 * second
}
}
if let item = pendingItems.first {
when.send(item, to: items) {
pendingItems.removeFirst()
}
}
}
}
func close() -> ErrorType? {
let errorChannel = Channel<ErrorType?>()
closing <- errorChannel
return !<-errorChannel
}
}
let fetcher = Fetcher(domain: "developer.apple.com/swift/blog/")
let subscription = Subscription(fetcher: fetcher)
after(5 * second) {
if let lastError = subscription.close() {
print("Closed with last error: \(lastError)")
} else {
print("Closed with no last error")
}
}
for item in subscription.updates {
print("\(item.domain): \(item.title)")
}###Output
developer.apple.com/swift/blog/: Swift 2.0
developer.apple.com/swift/blog/: Strings in Swift 2
developer.apple.com/swift/blog/: Swift-er SDK
developer.apple.com/swift/blog/: Swift 2 Apps in the App Store
Closed with last error: Network Error
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