The problem is that the main thread is deallocating the object before the other
thread has a chance to see it. Ideally you'd pass a managed object reference to
the block that runs in the other thread so the reference count does not fall to
zero. If you absolutely need to pass it as an unsafe pointer then you must
manage the reference count manually, like this:
let unsafePtr = Unmanaged.passRetained(self).toOpaque()
let safe =
Unmanaged<PointerTest>.fromOpaque(unsafePtr).takeRetainedValue()
useSafeObject(safe)
Make sure the calls to passRetained and takeRetainedValue are balanced. (If
this is a callback that gets called multiple times, use takeRetainedValue only
once at the end.)
> Le 18 juin 2017 à 9:23, Robert Nikander via swift-users
> <swift-users@swift.org> a écrit :
>
> Hi,
>
> I’m porting some C to Swift and I need to pass a Swift instance through a
> `void *` (ie, UnsafeMutableRawPointer). It works, in one thread, but when a
> second thread accesses the exact same pointer, it fails with memory errors
> like EXC_BAD_ACCESS
>
> The code below could be pasted into an AppDelegate.swift in a new single view
> iOS project.
>
> Anyone know what’s going on here? The second call to `tryUsingUnsafePointer`,
> in the new thread, crashes.
>
> Rob
>
>
> class PointerTest {
>
> let str = "Hello"
>
> init() { print("PointerTest.init") }
> deinit { print("PointerTest.deinit") }
>
> func start() {
> var mSelf = self
> let unsafePtr = UnsafeMutableRawPointer(&mSelf)
> tryUsingUnsafePointer(unsafePtr)
> print("Passing unsafe pointer to another thread: \(unsafePtr)")
>
> Thread.detachNewThread {
> tryUsingUnsafePointer(unsafePtr)
> }
> }
> }
>
> func tryUsingUnsafePointer(_ ptr: UnsafeMutableRawPointer) {
> print("Using unsafe pointer:")
> let typedPtr = ptr.assumingMemoryBound(to: PointerTest.self)
> // let typedPtr = ptr.bindMemory(to: PointerTest.self, capacity: 1)
> print(" typedPtr: \(typedPtr)")
> let obj = typedPtr.pointee
> print(" obj.str: \(obj.str)") // Memory error happening here, or
> sometimes line above
> }
>
>
> @UIApplicationMain
> class AppDelegate: UIResponder, UIApplicationDelegate {
>
> var window: UIWindow?
> var ptrTest: PointerTest?
>
> func application(_ application: UIApplication,
> didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey:
> Any]?) -> Bool {
>
> ptrTest = PointerTest()
> ptrTest?.start()
>
> return true
> }
>
> [...]
>
>
>
>
> _______________________________________________
> swift-users mailing list
> swift-users@swift.org
> https://lists.swift.org/mailman/listinfo/swift-users
--
Michel Fortin
https://michelf.ca
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