[SR-8036] deinit of global variables

[swift-ci]

Previous ID	SR-8036
Radar	None
Original Reporter	mrwerdo (JIRA User)
Type	Bug
Status	Resolved
Resolution	Won't Do

Attachment: Download

Environment

Xcode

Version 10.0 beta (10L176w)

Swift Version

Apple Swift version 4.2 (swiftlang-1000.0.16.7 clang-1000.10.25.3)
Target: x86_64-apple-darwin17.6.0

Additional Detail from JIRA

Votes	0
Component/s	Compiler
Labels	Bug
Assignee	None
Priority	Medium

md5: 05e05a93f64aace81cf33f2841e6c9e3

Issue Description:

Global variable's deinit methods are not called, but they should be.

The attached file produces the following output:

Read the image at: ~/Pictures/New York.png
Made the image black and white: ~/Pictures/New York.png
Read the image at: ~/Pictures/Sydney.png
Made the image black and white: ~/Pictures/Sydney.png
Saved the image: ~/Pictures/Sydney.png

There should be a second 'Save the image' line in the output, because there was two objects created.

The example also demonstrates how this problem can exhibit itself in real projects, files may not be saved/flushed before the program exits. Swift's guide actually lists this as a use case for `deinit` methods, "For example, if you create a custom class to open a file and write some data to it, you might need to close the file before the class instance is deallocated."

[belkadan]

Calling all global deinitializers would slow down program exit and could potentially lead to ordering problems. It's a deliberate feature of Swift that they are not called. If you want to have code run before a program exits, you'll have to register that code explicitly.