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Is UserDefaults thread safe in Swift? How to check it?


Is UserDefaults thread safe in Swift? How to check it?

By : KellyMoylan
Date : November 23 2020, 03:01 PM
fixed the issue. Will look into that further Is UserDefaults thread safe in Swift? How to check it? For example, if there 10 thread write data with UserDafaults. How we can check that is Thread Safe? , Yes it is:
code :


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Is Set in Swift 1.2 thread safe? If not how can I make it thread safe?

Is Set in Swift 1.2 thread safe? If not how can I make it thread safe?


By : user3709535
Date : March 29 2020, 07:55 AM
This might help you It is not thread safe. You can try to always access/update if from the same thread. Or protect it with locks, semaphores, etc.
UserDefaults swift as array check if value exists

UserDefaults swift as array check if value exists


By : Zohair Ahmed
Date : March 29 2020, 07:55 AM
I hope this helps . Use array(forKey. data(forKey is for (NS)Data objects.
You can check for nil and if the array contains the value in one expression:
code :
let defaults = UserDefaults.standard
if let seenPosts = defaults.array(forKey: "seen_posts") as? [Int], !seenPosts.contains(5) {
    seenPosts.insert(CellsData[indexPath.row]["id"] as! Int, at: 0)

}
Thread 1: EXC_BAD_INSTRUCTION when encoding data in UserDefaults (Swift)

Thread 1: EXC_BAD_INSTRUCTION when encoding data in UserDefaults (Swift)


By : Christian
Date : March 29 2020, 07:55 AM
Hope that helps Hi, I am trying to save data in Userdefaults but whenever I run this page of the app I am getting Thread 1: EXC_BAD_INSTRUCTION (code=EXC_I386_INVOC) as shown in the image. , Try using
code :
highScore =  defaults.integer(forKey: "Add1High")
defaults.set(highScore, forKey: "Add1High")
Swift: How to check if UserDefaults exists and if not save a chosen standard value?

Swift: How to check if UserDefaults exists and if not save a chosen standard value?


By : Scott
Date : March 29 2020, 07:55 AM
fixed the issue. Will look into that further The problem is you can't determine exists with UserDefaults.standard.bool(forKey: key). UserDefaults.standard.object(forKey: key) returns Any? so you can use it to test for nil e.g.
code :
extension UserDefaults {

    static func exists(key: String) -> Bool {
        return UserDefaults.standard.object(forKey: key) != nil
    }

}
Double check lock optimization to implement thread-safe lazy-loading in Swift

Double check lock optimization to implement thread-safe lazy-loading in Swift


By : Jackie.Qi
Date : March 29 2020, 07:55 AM
fixed the issue. Will look into that further IMO, the correct tool here is os_unfair_lock. The point of double-check locking is to avoid the expense of a full kernel lock. os_unfair_lock provides that in the uncontested case. The "unfair" part of it is that it doesn't make promises to waiting threads. If one thread unlocks, it is allowed to relock without another waiting thread getting a chance (and thus could starve). In practice with a very small critical section, this is not relevant (in this case you're just checking a local variable against nil). It is a lower-level primitive than dispatching to a queue, which is very fast, but not as fast as an unfair_lock, since it relies on primitives like unfair_lock.
code :
final class Builder<I> {

    private let body: () -> I
    private var lock = os_unfair_lock()

    init(body: @escaping () -> I) {
        self.body = body
    }

    private var _value: I!
    var value: I {
        os_unfair_lock_lock(&lock)
        if _value == nil {
            _value = body()
        }
        os_unfair_lock_unlock(&lock)

        return _value
    }
}
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