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swiftconcurrencygrand-central-dispatchnsoperationqueue
Kishoretheju
Kishoretheju

Reputation: 957

Is there a way we might face race condition when running async tasks on serial queue

Suppose if multiple async tasks running in a serial queue are accessing a same shared resource, are there any chances we might face race condition?

Upvotes: 2

Views: 1706

Answers (2)

Jagermeiste
Jagermeiste

Reputation: 1

No you can not run into a race condition, see what I did there, when running async tasks on a serial queue due to the fact that the type of queue has to deal with the ways the tasks are executed and while synchrony and asynchrony has to deal with the responsiveness of your application when completing an expensive task.

The reason it is easy to run into a race condition when on a concurrrent queue because on a concurrent queue tasks are allowed to be executed at the same time therefore different threads sometimes may be "racing" to perform an action and in all actuality they are overwriting the previous threads work due to the threads performing the same action. Where as on a serial queue tasks are executed one at a time so two threads cant race to complete a task because it happens in sequential order. Hope that helps!

Upvotes: 0

Lorenzo B
Lorenzo B

Reputation: 33428

Following the comment I've added, this is taken from Apple doc. In bold I put the emphasis to what you are looking for.

Serial queues (also known as private dispatch queues) execute one task at a time in the order in which they are added to the queue. The currently executing task runs on a distinct thread (which can vary from task to task) that is managed by the dispatch queue. Serial queues are often used to synchronize access to a specific resource.

If you are using a concurrent queue instead you could have a race condition. You can prevent it using dispatch barriers, for example. See Grand Central Dispatch In-Depth: Part 1/2 for more details.

For NSOperation and NSOperationQueue the same applies. NSOperationQueue can be made serial with maxConcurrentOperationCount set to 1. In addition, using dependencies through operations, you can synchronize the access to a shared resource.

Upvotes: 1

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