使用 LET 定义的 Swift 常量有时会在读取 (OSX) 时产生 EXC_BAD_ACCESS (EXC_I386_GPFLT)

Question

In my AppDelegate I have a constant for a statusbar icon, used when the application is busy:

class AppDelegate: NSObject, NSApplicationDelegate {

let busyImage = NSImage(named: "BusyStatus");
...

In another class I'm accessing this several times over the time the app is running. On a Macbook Air with SSD I sometimes get an

EXC_BAD_ACCESS (SIGSEGV)
Exception Codes:       EXC_I386_GPFLT

Thread 0 Crashed:: Dispatch queue: com.apple.main-thread
0   libswiftCore.dylib              0x0000000103876cf9 swift_unknownRetain + 41
1   de.test.myapp   0x000000010304743b TestApp.AppDelegate.busyImage.getter : ObjectiveC.NSImage? (in TestApp) (AppDelegate.swift:0)
2   de.test.myapp   0x0000000102f9aa77 TestApp.Sync.(update (TestApp.Sync) -> () -> ()).(closure #2) (in TestApp) (Sync.swift:271)

The code there:

statusBarItem!.image = appDelegate!.busyImage

It's in a block called in the Main Thread:

let updateBlock: () -> () = {

    appDelegate!.statusBarItem!.image = self.appDelegate!.busyImage
        [... other code ...]
 }

 if NSThread.isMainThread()
 {
     updateBlock()
 }
 else
 {
     dispatch_sync(dispatch_get_main_queue(),updateBlock)
 }

What can cause this and how to avoid this?

Answer 1

问题似乎从 swift 2 开始就消失了。再也没有这个问题并且我的代码中没有任何改变。

Answer 2

Hello People from the Internet,

My env is macOS 10.15.4 and I am running XCode 11.5 (11E608c) with Swift 5.

I have exactly the same issue with a little piece of code here which fails 100% of the time when using the rotation:

override func rotate(delta: float2) {
    let sensitivity: Float = 0.005
    rotation.y += delta.x * sensitivity    // FAILS with Thread 1: EXC_BAD_ACCESS (code=EXC_I386_GPFLT)
    _viewMatrix = updateViewMatrix()
}

This code does not look weird at all. rotation is a vector of floats defined in the Class as:

var rotation: float3 = [0, 0, 0]

Now, I spent some time trying many versions of the same function and if I rewrite it as:

override func rotate(delta: float2) {
    let sensitivity: Float = 0.005
    var deltaX: Float = delta.x * sensitivity
    rotation.y += deltaX
    _viewMatrix = updateViewMatrix()
}

it now runs smoothly. This is crazy since I see no obvious reason. I do not try to change a constant and even the linter advises me to change the var to let in deltaX definition.

I feel like this is a Swift issue but this is worrying for a 5th version of a language used by many.

I would update my answer if I find a solution or at least a valid explanation.

Live long and prosper lads!