Question: What Is Atomic And Nonatomic In IOS?

What are atomic writes?

In computer science, read–modify–write is a class of atomic operations (such as test-and-set, fetch-and-add, and compare-and-swap) that both read a memory location and write a new value into it simultaneously, either with a completely new value or some function of the previous value..

Does copy increase retain count?

No, a copied object will have a retain count of 1, just like a newly initialized object. I highly recommend you read the Memory Management Guide if you wish to learn more. If you’re new to iOS development, the iOS App Programming Guide should be read first, and is a great use of your time.

What is retain count?

Retain Count represents number of owners for a particular object. It is zero till object does not have any owners. Increase in one ownership claim will cause retain count to increase by 1 and decrease will cause it to decrement by 1. Example: – Class A object is created using alloc/init and retain count is 1.

What is atomic Swift?

Atomic property is one of the commonly-requested Swift features, that exists in Objective-C. By default, an Objective-C property is atomic. … There are many kinds of locks that are available in Swift via different Apple’s frameworks APIs: NSLock , pthread_mutex_t – mutex that allows access to only one thread at a time.

What is retain in IOS?

You send an object a retain message when you want to prevent it from being deallocated until you have finished using it. An object is deallocated automatically when its reference count reaches 0 . retain messages increment the reference count, and release messages decrement it.

What is atomic load?

When an atomic load is performed on a shared variable, it reads the entire value as it appeared at a single moment in time. … Any time two threads operate on a shared variable concurrently, and one of those operations performs a write, both threads must use atomic operations.

What is atomic API?

Atomicity. In computer programming, an operation done by a computer is considered atomic if it is guaranteed to be isolated from other operations that may be happening at the same time. Put another way, atomic operations are indivisible. Atomic operations are critically important when dealing with shared resources.

Why do we use atomic and non atomic and what is default Behaviour?

Atomic:- is the default behavior. it will ensure the present process is completed by the CPU, before another process accesses the variable.it is not fast, as it ensures the process is completed entirelyNon-Atomic: – is NOT the default behavior.

Is atomic thread safe?

7. Atomic Objects. It’s also possible to achieve thread-safety using the set of atomic classes that Java provides, including AtomicInteger, AtomicLong, AtomicBoolean, and AtomicReference. Atomic classes allow us to perform atomic operations, which are thread-safe, without using synchronization.

What is thread safe in Swift?

Thread safe is a concept in the context of multi-thread and it means any shared data is accessed by only one thread at any given time. If you want to write/read access to a shared resource from different threads, you should take the thread safety into consideration.

Is count ++ an atomic?

If you will run above program, you will notice that count value varies between 5,6,7,8. The reason is because count++ is not an atomic operation. So by the time one threads read it’s value and increment it by one, other thread has read the older value leading to wrong result.

What is the difference between atomic and nonatomic properties in IOS?

Atomic means only one thread accesses the variable (static type). Atomic is thread-safe, but it is slow. Nonatomic means multiple threads access the variable (dynamic type). Nonatomic is thread-unsafe, but it is fast.

What is the strong attribute of property?

strong / retain : Declaring strong means that you want to “own” the object you are referencing. Any data that you assign to this property will not be destroyed as long as you or any other object points to it with a strong reference.

What is Nonatomic?

Nonatomic means multiple thread access the variable (dynamic type). … it may result in unexpected behavior, when two different process (threads) access the same variable at the same time.

What is NSLock?

An NSLock is a mutex; it prevents multiple threads from accessing the same resource simultaneously, which is exactly what you want to do here. Once one thread acquires the lock, other threads attempting to acquire the lock will wait until the first thread releases the lock.

What is Property in iOS?

They define memory management, type, and access attributes of the values they store such as strong , weak , assign , readonly , readwrite , etc. Properties store values assigned to them in an instance variable that by convention has the same name as the property but starts with an underscore prefix.