Fix `schedule(after:interval:leeway:)` disposal #584

jjoelson · 2017-12-28T17:00:12Z

Addresses #582. Retain timers in QueueScheduler so that they will not be cancelled if the user doesn’t retain the returned Disposable.

Note that the test leaks a timer, but I'm not sure how else to test that the timer continues running even when the Disposable is not retained.

Checklist

Updated CHANGELOG.md.

Retain timers in `QueueScheduler` so that they will not be cancelled if the user doesn’t retain the returned `Disposable`.

andersio

Thanks for the PR. 😸

The timers would be released upon deinitialisation of the scheduler, so there should have no leakage AFAICU.

andersio · 2017-12-28T19:05:20Z

Tests/ReactiveSwiftTests/SchedulerSpec.swift

+						expect(false).to(equal(true), description: "timer not cancelled on disposal")
+					}
+
+					scheduler.schedule(after: Date(), interval: .milliseconds(10), leeway: .seconds(0)) {


You might scope the scheduling call in a function, so that the disposable is guaranteed to be deinitialised.

andersio · 2017-12-28T19:07:03Z

Tests/ReactiveSwiftTests/SchedulerSpec.swift

+					var count = 0
+					let timesToIncrement = 3
+
+					// Start two repeating timers, dispose the first, and ensure only the second runs.


It'd probably be better off as two separate test cases. One for cancellation, while another for not retaining the disposable.

andersio · 2017-12-28T19:08:45Z

Sources/Scheduler.swift

@@ -193,8 +193,14 @@ public final class QueueScheduler: DateScheduler {

 	public let queue: DispatchQueue

+	private let lock: Lock
+
+	private var timers: [DispatchSourceTimer]


You may use Atomic. I'd prefer Set which fits the scenario here (insert/removal only).

DispatchSourceTimer isn't Hashable, so I think it would have to be an NSMutableSet. Is that an improvement over using a Swift array?

andersio · 2017-12-28T19:12:28Z

CHANGELOG.md

@@ -1,6 +1,8 @@
 # master
 *Please add new entries at the top.*

+1. Fixed `schedule(after:interval:leeway:)` being cancelled when the returned `Disposable` is not retained.


Please add the PR no & your handle.

andersio · 2017-12-28T19:16:09Z

Tests/ReactiveSwiftTests/SchedulerSpec.swift

+					// Start two repeating timers, dispose the first, and ensure only the second runs.
+
+					disposable.inner = scheduler.schedule(after: Date(), interval: .milliseconds(10), leeway: .seconds(0)) {
+						expect(false).to(equal(true), description: "timer not cancelled on disposal")


You may replace this with fail("message").

andersio · 2017-12-28T19:18:38Z

Tests/ReactiveSwiftTests/SchedulerSpec.swift

+
+					expect(count) == 0
+
+					scheduler.queue.resume()


For the cancellation test, I'd wait for 1.5-2x the interval after resuming the queue so that the test case could actually fail.

andersio · 2017-12-29T08:21:40Z

A private wrapper for DispatchSourceTimer would work. The hash value & the equality can be derived from the object identity with ObjectIdentifier and ===.

andersio · 2017-12-29T16:55:08Z

Sources/Scheduler.swift

+	private let value: DispatchSourceTimer
+
+	fileprivate var hashValue: Int {
+		return value.hash


Please use ObjectIdentifier(value).hashValue. The Dispatch protocol hierarchies do not inherit from NSObjectProtocol on platforms w/o ObjC interop.

andersio · 2017-12-29T16:56:38Z

Sources/Scheduler.swift

 		timers.modify { timers in
-			timers.append(timer)
+			timers.insert(wrappedTimer)
 		}

 		return AnyDisposable {
 			timer.cancel()

 			self.timers.modify { timers in


Could we weakify self here?

andersio · 2017-12-29T16:59:15Z

Tests/ReactiveSwiftTests/SchedulerSpec.swift

+						count += 1
+
+						if count == timesToRun {
+							disposable1.dispose()


This should be disposable2. The macOS CI seems failing because of this.

andersio · 2017-12-29T17:04:36Z

Tests/ReactiveSwiftTests/SchedulerSpec.swift

+					expect(count) == 0
+
+					scheduler.queue.resume()
+					expect{count}.toEventually(equal(timesToIncrement))


IIRC expect uses @autoclosure, so it is already implicitly captured.

andersio · 2017-12-29T17:04:53Z

Tests/ReactiveSwiftTests/SchedulerSpec.swift

+
+					// This expectation should take about 2.0 * interval to be fulfilled, and that's
+					// enough time to ensure that the first timer was actually cancelled.
+					expect{count}.toEventually(equal(timesToRun))


Ditto for @autoclosure.

andersio · 2017-12-29T19:22:50Z

Hmm

ReactiveSwiftTests.SchedulerSpec
  QueueScheduler__on_a_given_queue__should_repeatedly_run_actions_after_a_given_date_when_the_disposable_is_not_retained, expected to eventually equal <3>, got <4>

jjoelson · 2017-12-29T19:30:43Z

I think I see the bug, but strange that it’s not failing on my machine. I guess there’s a race condition where the expectation sees that it got incremented to 3 and succeeds before it gets incremented that last time.

I will fix when I get back to my PC.

andersio · 2017-12-29T19:55:32Z

CI has limited concurrency (1 logical processor IIRC).

Specify `pollInterval` on the asynchronous expectation to avoid false positive test success.

jjoelson · 2018-01-02T13:24:24Z

Is there a test still failing on Linux? I'm having a tough time understanding the log.

jjoelson · 2018-01-02T14:27:53Z

OK, I found the error on Linux:

/home/travis/build/ReactiveCocoa/ReactiveSwift/Sources/Scheduler.swift:185:10: error: cannot invoke initializer for type 'ObjectIdentifier' with an argument list of type '(DispatchSourceTimer)'
                return ObjectIdentifier(value).hashValue
                       ^
/home/travis/build/ReactiveCocoa/ReactiveSwift/Sources/Scheduler.swift:185:10: note: overloads for 'ObjectIdentifier' exist with these partially matching parameter lists: (AnyObject), (Any.Type)
                return ObjectIdentifier(value).hashValue
                       ^
/home/travis/build/ReactiveCocoa/ReactiveSwift/Sources/Scheduler.swift:193:20: error: binary operator '===' cannot be applied to two 'DispatchSourceTimer' operands
                return lhs.value === rhs.value
                       ~~~~~~~~~ ^   ~~~~~~~~~
/home/travis/build/ReactiveCocoa/ReactiveSwift/Sources/Scheduler.swift:193:20: note: overloads for '===' exist with these partially matching parameter lists: (AnyObject?, AnyObject?), (NSNull?, NSNull?), (AnyClass, AnyClass)
                return lhs.value === rhs.value

Will fix when I get home tonight.

`DispatchSourceTimer` doesn’t inherit from `NSObjectProtocol` on Linux. Basing hashing and equality on the wrapper is sufficient because the same wrapper instance can be used insert and remove from the `Set` of retained timers.

jjoelson · 2018-01-03T04:08:25Z

Stumped by this one:

2018-01-02 23:49:31.857 xcodebuild[2551:9128] Error 2018-01-02 23:49:31.857 xcodebuild[2551:9128] Error Domain=IDETestOperationsObserverErrorDomain Code=6 "Early unexpected exit, operation never finished bootstrapping - no restart will be attempted" UserInfo={NSLocalizedDescription=Early unexpected exit, operation never finished bootstrapping - no restart will be attempted}

** TEST EXECUTE FAILED **

mdiep · 2018-01-03T12:22:22Z

Usually that's downstream from whatever the actual error was.

jjoelson · 2018-01-03T13:40:05Z

Seems to be working now. Judging by this Stackoverflow thread, that's an error that can occur randomly.

Fix schedule(after:interval:leeway:) disposal

421f86c

Retain timers in `QueueScheduler` so that they will not be cancelled if the user doesn’t retain the returned `Disposable`.

andersio requested changes Dec 28, 2017

View reviewed changes

andersio reviewed Dec 28, 2017

View reviewed changes

jjoelson added 3 commits December 28, 2017 14:39

Add pull request # and handle

4c47d4e

Use Atomic instead of Lock

07570af

Separate the tests for repeated action disposal

bed149e

Use Set instead of Array to store timers

74667b2

andersio requested changes Dec 29, 2017

View reviewed changes

jjoelson added 3 commits December 29, 2017 14:01

Use ObjectIdentifier(value).hashValue

2fb93cf

Weakify self in the returned Disposable

4a4bebc

Fix QueueScheduler tests

8e3299b

Fix increment in test

90f69c6

Specify `pollInterval` on the asynchronous expectation to avoid false positive test success.

Conform to timer wrapper to Hashable by self ref

7911a73

`DispatchSourceTimer` doesn’t inherit from `NSObjectProtocol` on Linux. Basing hashing and equality on the wrapper is sufficient because the same wrapper instance can be used insert and remove from the `Set` of retained timers.

andersio approved these changes Jan 4, 2018

View reviewed changes

andersio merged commit 8fa0921 into ReactiveCocoa:master Jan 5, 2018

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Fix `schedule(after:interval:leeway:)` disposal #584

Fix `schedule(after:interval:leeway:)` disposal #584

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Fix schedule(after:interval:leeway:) disposal #584

Fix schedule(after:interval:leeway:) disposal #584

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jjoelson commented Dec 28, 2017

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Fix `schedule(after:interval:leeway:)` disposal #584

Fix `schedule(after:interval:leeway:)` disposal #584

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