swift playground / deinit {}中的内存泄漏并未始终如一地调用 [英] Memory leaks in the swift playground / deinit{} not called consistently

问题描述

ARC对象删除似乎在Swift Playground中不一致。它是一个bug还是设计？

ARC object deletion seems to be inconsistent in the Swift Playground. Is it a bug or by design?

考虑这个类：

class Test {
  var name: String
  init(name:String){
    self.name = name
    println("\(name) initialized")
  }
  deinit{
    println("\(name) deinitialized")
  }
}

当我从操场上调用它时（不是命令行REPL，请参阅下面的评论）：

When I call it from the playground (not the command line REPL, see comment below):

var t1 = Test(name: "t1")
var t2 : Test? = Test(name: "t2")
t2 = nil

我只看到初始化消息在控制台中：

I see only initialization messages in the console:

t1 initialized
t2 initialized

缺少的是t2的deinit。

What's missing is deinit of t2.

当我在应用程序中运行它时（例如，应用代表的输入） ），输出与ARC删除一致（即t1 init，然后t2，t2 deinit然后t1，因为整个调用块超出范围）：

When I run it in an app (e.g. entry of app delegate), I the output is consistent with ARC deletion (i.e. t1 init, then t2, and t2 deinit and then t1, since the entire invocation block goes out of scope):

t1 initialized
t2 initialized
t2 deinitialized
t1 deinitialized

最后，在命令行REPL中（请参阅下面的注释以访问REPL），结果是明确的，即：t1由于其顶级范围而处于活动状态，但是t2被ARC删除，如人们会期待。

Finally, in the command line REPL (see comment below for accessing the REPL), the results are consisent, i.e.: t1 is alive due to its top level scope, but t2 is ARC deleted, as one would expect.

  1> class Test {
  2.       var name: String
  3.       init(name:String){
  4.               self.name = name
  5.               println("\(name) initialized")
  6.       }
  7.       deinit{
  8.               println("\(name) deinitialized")
  9.       }
 10. }
 11> var t1 = Test(name: "t1")
t1 initialized
t1 initialized
t1 deinitialized
t1: Test = {
  name = "t1"
}
 12> var t2 : Test? = Test(name: "t2")
t2 initialized
t2 initialized
t2 deinitialized
t2: Test? = (name = "t2")
 13> t2 = nil
t2 deinitialized
 14> t1
$R2: Test = {
  name = "t1"
}
 15> t2
$R3: Test? = nil

推荐答案

我们比较了ARC /删除异议应用场景和游乐场内。我们的测试代码使用在特定范围内外创建的对象。我们还嵌套了测试对象以测试多嵌套作用域。

We compared ARC/deletion of objection in an app scenario and within the Playground. Our test code used object created inside and outside a particular scope. We also nested the tester object to test multi-nested scoping.

我们看到应用场景在cue上删除了对象（第0个引用），而Playground场景删除了一些，但保留了多数对象（无论范围如何，但在多次运行中显然是一致的）。

We saw that the app scenario deletes objects right on cue (zeroth reference) whereas the Playground scenario deletes a few, but holds on to a majority of objects (irrespective of scope, but apparently consistent over multiple runs).

Playground可能会保留对象以便为其辅助GUI输出（和/或其播放功能）提供服务。

The Playground probably holds on to objects in order to service its assistant GUI output (and/or its playback feature).

参见博文这里。

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