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An equivalent of Go's select
statement?
#28
Comments
@ckornher I'm not familiar with go lang, but // Message types for actor
enum CounterMessages {
case increment, getCounter(CoPromise<Int>)
}
let actor = DispatchQueue.global().actor(of: CounterMessages.self) { receiver in
var counter = 0
for message in receiver {
switch message {
case .increment:
counter += 1
case .getCounter(let promise):
promise.success(counter)
}
}
}
DispatchQueue.concurrentPerform(iterations: 100_000) { _ in
actor.offer(.increment)
}
let promise = CoPromise<Int>()
promise.whenSuccess { print($0) }
actor.offer(.getCounter(promise))
actor.close() |
In golang you can use select to read from multiple channels in the same coroutine. for i := 0; i < n; i++ {
select {
case msgFromChannel1 := <-channel1:
println("received", msgFromChannel1)
case msgFromChannel2 := <-channel2:
println("received", msgFromChannel2)
}
} |
@FabianTerhorst @ckornher Hi, it looks really great in golang. We can create some "select" channel to combine results from several channels. It may look something like this (may still need to think about which channel closes or cancels whom): extension CoChannel {
func addSubchannel(_ channel: CoChannel) {
// Cancel subchannel on complete
whenComplete(channel.cancel)
// Offer value when receive result
channel.whenReceive { _ = $0.map(self.offer) }
}
func addSubchannel<T>(_ channel: CoChannel<T>, transformer: @escaping (T) -> Element) {
// Cancel subchannel on complete
whenComplete(channel.cancel)
// Offer value when receive result
channel.whenReceive { result in
guard let value = try? result.get() else { return }
self.offer(transformer(value))
}
}
} Then the use may look like this: enum Foo {
case caseA(Int), caseB(String)
}
let channelA: CoChannel<Int>
let channelB: CoChannel<String>
let selectChannel = CoChannel<Foo>()
selectChannel.addSubchannel(channelA, transformer: Foo.caseA)
selectChannel.addSubchannel(channelB, transformer: Foo.caseB)
DispatchQueue.global().startCoroutine {
for foo in selectChannel.makeIterator() {
switch foo {
case .caseA(let a):
print(a)
case .caseB(let b):
print(b)
}
}
} |
Yes, this would work except that I think that it suffers from the same problem that I ran into when I tried to use the library as-is. I could not avoid a case where the logic captures values from the "subchannels" while an element is being processed. Golang never buffers elements within a Golang's select is often used to have a measure of "out-of-band" control over a "goroutine" and buffering would defeat this sort of logic. Golang Golang's I do not see a way around something like a multi-channel |
@ckornher @FabianTerhorst Thank you for explanation. It seems that |
…detect mods to free blocks SwiftCoroutineDemo(39856,0x11266e600) malloc: nano zone abandoned due to inability to preallocate reserved vm space. DispatchQueue::scheduleTask() <OS_dispatch_queue_main: com.apple.main-thread> SharedCoroutineDispatcher::getFreeQueue(SwiftCoroutine.SharedCoroutineDispatcher) CoroutineContext::init(stackSize=196608, guardPage=true, SwiftCoroutine.CoroutineContext) returnEnv = 0x000060f0000042d0 stack = 0x000000010effb000 SharedCoroutineQueue::start(SwiftCoroutine.SharedCoroutineQueue) CoroutineContext::start(SwiftCoroutine.CoroutineContext) enter CoroutineContext::stackTop(SwiftCoroutine.CoroutineContext) 0x000000010f02b000 CoroutineContext::start(Optional(0x00006060000b8400)) block enter ==39856==WARNING: ASan is ignoring requested __asan_handle_no_return: stack type: default top: 0x7ff7b7045000; bottom 0x00010f028000; size: 0x7ff6a801d000 (140697357373440) False positive error reports may follow For details see google/sanitizers#189 CoroutineContext::start(SwiftCoroutine.CoroutineContext) leave DispatchQueue::scheduleTask() <OS_dispatch_queue_main: com.apple.main-thread> SharedCoroutineDispatcher::getFreeQueue(SwiftCoroutine.SharedCoroutineDispatcher) SharedCoroutineQueue::start(SwiftCoroutine.SharedCoroutineQueue) CoroutineContext::stackTop(SwiftCoroutine.CoroutineContext) 0x000000010f02b000 ================================================================= ==39856==ERROR: AddressSanitizer: stack-buffer-overflow on address 0x00010f029ec1 at pc 0x00010949d77d bp 0x7ff7b7040e90 sp 0x7ff7b7040650 READ of size 4416 at 0x00010f029ec1 thread T0 #0 0x10949d77c in wrap_memcpy+0x16c (libclang_rt.asan_iossim_dynamic.dylib:x86_64+0x1977c) belozierov#1 0x109ef7f83 in SharedCoroutine.saveStack() SharedCoroutine.swift:79 belozierov#2 0x109eff514 in SharedCoroutineQueue.start(dispatcher:scheduler:task:) SharedCoroutineQueue.swift:39 belozierov#3 0x109efc229 in closure belozierov#1 in SharedCoroutineDispatcher.execute(on:task:) SharedCoroutineDispatcher.swift:27 belozierov#4 0x109ee7ed9 in OS_dispatch_queue.scheduleTask(_:) CoroutineScheduler+DispatchQueue.swift:16 belozierov#5 0x109ee88ad in protocol witness for CoroutineScheduler.scheduleTask(_:) in conformance OS_dispatch_queue <compiler-generated> belozierov#6 0x109efbf48 in SharedCoroutineDispatcher.execute(on:task:) SharedCoroutineDispatcher.swift:26 belozierov#7 0x109ee3616 in CoroutineScheduler._startCoroutine(_:) CoroutineScheduler.swift:51 belozierov#8 0x109ee3c78 in CoroutineScheduler.startCoroutine(in:task:) CoroutineScheduler.swift:69 belozierov#9 0x108ebe2ed in AppDelegate.test() AppDelegate.swift:43 belozierov#10 0x108ebdd77 in AppDelegate.application(_:didFinishLaunchingWithOptions:) AppDelegate.swift:18 belozierov#11 0x108ebe4b7 in @objc AppDelegate.application(_:didFinishLaunchingWithOptions:) <compiler-generated> belozierov#12 0x7fff2509a592 in -[UIApplication _handleDelegateCallbacksWithOptions:isSuspended:restoreState:]+0xd5 (UIKitCore:x86_64+0xcd7592) belozierov#13 0x7fff2509c283 in -[UIApplication _callInitializationDelegatesWithActions:forCanvas:payload:fromOriginatingProcess:]+0x101f (UIKitCore:x86_64+0xcd9283) belozierov#14 0x7fff250a1c23 in -[UIApplication _runWithMainScene:transitionContext:completion:]+0x4a5 (UIKitCore:x86_64+0xcdec23) belozierov#15 0x7fff246124a2 in -[_UISceneLifecycleMultiplexer completeApplicationLaunchWithFBSScene:transitionContext:]+0xb2 (UIKitCore:x86_64+0x24f4a2) belozierov#16 0x7fff2509e2ac in -[UIApplication _compellApplicationLaunchToCompleteUnconditionally]+0x3a (UIKitCore:x86_64+0xcdb2ac) belozierov#17 0x7fff2509e64b in -[UIApplication _run]+0x391 (UIKitCore:x86_64+0xcdb64b) belozierov#18 0x7fff250a32b4 in UIApplicationMain+0x64 (UIKitCore:x86_64+0xce02b4) belozierov#19 0x7fff59d55cc1 in UIApplicationMain(_:_:_:_:)+0x61 (libswiftUIKit.dylib:x86_64+0x21cc1) belozierov#20 0x108ebf357 in static UIApplicationDelegate.main() <compiler-generated> belozierov#21 0x108ebf2a0 in static AppDelegate.$main() AppDelegate.swift:11 belozierov#22 0x108ebfc77 in main <compiler-generated> belozierov#23 0x1090f8f20 in start_sim+0x9 (dyld_sim:x86_64+0x1f20) belozierov#24 0x1125f352d (<unknown module>) 0x00010f029ec1 is located 192193 bytes inside of 200704-byte region [0x00010effb000,0x00010f02c000) allocated by thread T0 here: #0 0x1094c7bb3 in wrap_posix_memalign+0xb3 (libclang_rt.asan_iossim_dynamic.dylib:x86_64+0x43bb3) belozierov#1 0x7fff30c9e62c in swift_slowAlloc+0x4c (libswiftCore.dylib:x86_64+0x30762c) belozierov#2 0x109ede243 in CoroutineContext.init(stackSize:guardPage:) CoroutineContext.swift:32 belozierov#3 0x109eddc1f in CoroutineContext.__allocating_init(stackSize:guardPage:) CoroutineContext.swift belozierov#4 0x109efe985 in SharedCoroutineQueue.init(stackSize:) SharedCoroutineQueue.swift:28 belozierov#5 0x109efe5c3 in SharedCoroutineQueue.__allocating_init(stackSize:) SharedCoroutineQueue.swift belozierov#6 0x109efcb3d in SharedCoroutineDispatcher.getFreeQueue() SharedCoroutineDispatcher.swift:38 belozierov#7 0x109efc20d in closure belozierov#1 in SharedCoroutineDispatcher.execute(on:task:) SharedCoroutineDispatcher.swift:27 belozierov#8 0x109ee7ed9 in OS_dispatch_queue.scheduleTask(_:) CoroutineScheduler+DispatchQueue.swift:16 belozierov#9 0x109ee88ad in protocol witness for CoroutineScheduler.scheduleTask(_:) in conformance OS_dispatch_queue <compiler-generated> belozierov#10 0x109efbf48 in SharedCoroutineDispatcher.execute(on:task:) SharedCoroutineDispatcher.swift:26 belozierov#11 0x109ee3616 in CoroutineScheduler._startCoroutine(_:) CoroutineScheduler.swift:51 belozierov#12 0x109ee3c78 in CoroutineScheduler.startCoroutine(in:task:) CoroutineScheduler.swift:69 belozierov#13 0x108ebe2ed in AppDelegate.test() AppDelegate.swift:43 belozierov#14 0x108ebdd77 in AppDelegate.application(_:didFinishLaunchingWithOptions:) AppDelegate.swift:18 belozierov#15 0x108ebe4b7 in @objc AppDelegate.application(_:didFinishLaunchingWithOptions:) <compiler-generated> belozierov#16 0x7fff2509a592 in -[UIApplication _handleDelegateCallbacksWithOptions:isSuspended:restoreState:]+0xd5 (UIKitCore:x86_64+0xcd7592) belozierov#17 0x7fff2509c283 in -[UIApplication _callInitializationDelegatesWithActions:forCanvas:payload:fromOriginatingProcess:]+0x101f (UIKitCore:x86_64+0xcd9283) belozierov#18 0x7fff250a1c23 in -[UIApplication _runWithMainScene:transitionContext:completion:]+0x4a5 (UIKitCore:x86_64+0xcdec23) belozierov#19 0x7fff246124a2 in -[_UISceneLifecycleMultiplexer completeApplicationLaunchWithFBSScene:transitionContext:]+0xb2 (UIKitCore:x86_64+0x24f4a2) belozierov#20 0x7fff2509e2ac in -[UIApplication _compellApplicationLaunchToCompleteUnconditionally]+0x3a (UIKitCore:x86_64+0xcdb2ac) belozierov#21 0x7fff2509e64b in -[UIApplication _run]+0x391 (UIKitCore:x86_64+0xcdb64b) belozierov#22 0x7fff250a32b4 in UIApplicationMain+0x64 (UIKitCore:x86_64+0xce02b4) belozierov#23 0x7fff59d55cc1 in UIApplicationMain(_:_:_:_:)+0x61 (libswiftUIKit.dylib:x86_64+0x21cc1) belozierov#24 0x108ebf357 in static UIApplicationDelegate.main() <compiler-generated> belozierov#25 0x108ebf2a0 in static AppDelegate.$main() AppDelegate.swift:11 belozierov#26 0x108ebfc77 in main <compiler-generated> belozierov#27 0x1090f8f20 in start_sim+0x9 (dyld_sim:x86_64+0x1f20) belozierov#28 0x1125f352d (<unknown module>) SUMMARY: AddressSanitizer: stack-buffer-overflow (libclang_rt.asan_iossim_dynamic.dylib:x86_64+0x1977c) in wrap_memcpy+0x16c Shadow bytes around the buggy address: 0x0001344ad380: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x0001344ad390: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x0001344ad3a0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x0001344ad3b0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x0001344ad3c0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 =>0x0001344ad3d0: 00 00 00 00 f1 f1 f1 f1[01]f3 f3 f3 00 00 00 00 0x0001344ad3e0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x0001344ad3f0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x0001344ad400: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x0001344ad410: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x0001344ad420: 00 00 00 00 00 00 00 00 00 00 00 00 ca ca ca ca Shadow byte legend (one shadow byte represents 8 application bytes): Addressable: 00 Partially addressable: 01 02 03 04 05 06 07 Heap left redzone: fa Freed heap region: fd Stack left redzone: f1 Stack mid redzone: f2 Stack right redzone: f3 Stack after return: f5 Stack use after scope: f8 Global redzone: f9 Global init order: f6 Poisoned by user: f7 Container overflow: fc Array cookie: ac Intra object redzone: bb ASan internal: fe Left alloca redzone: ca Right alloca redzone: cb ==39856==ABORTING AddressSanitizer report breakpoint hit. Use 'thread info -s' to get extended information about the report. (lldb)
Another feature request:
Go has a
select
statement that facilitates the use of multiple channels simultaneously for timers, out-of-band control, etc.Are you planning to add something similar?
https://tour.golang.org/concurrency/5
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