CODEWITHSUNDEEP
javamultithreading
Dmitry Zinkevich
Dmitry Zinkevich

Reputation: 3623

How to safely share ArrayDeque between multiple threads?

Recently I started reading 'Java 7 Concurrency Cookbook' and in a section Creating and running a daemon thread found the code where main thread creates and one instance of ArrayDeque and shares its reference with three producers and one consumer. The producers call deque.addFirst(event) and the consumer calls deque.getLast().

But JavaDoc of ArrayDeque clearly states that:

Array deques are not thread-safe; in the absence of external synchronization, they do not support concurrent access by multiple threads.

So I wonder whether it is a mistake or I just don't understand something?

Upvotes: 4

Views: 4145

Answers (2)

Jeril Kuruvila
Jeril Kuruvila

Reputation: 19960

Array deques are not thread safe, meaning you have to provide external synchronization.

However why it works is, like holger said Deque methods

You are using addFirst(e) is an insert model method which does causes change in underlying datastructure

You are using getLast() which is an examine model method which does not causes change in underlying datastructure.

That is why it is working, if you had used removeLast() instead of getLast(), you should have got ConcurrentModification Exception for sure.

Hope this clears up everything , Cheers

Upvotes: 2

Shikhar Upadhyay
Shikhar Upadhyay

Reputation: 7

It is clearly mentioned that if you are not going to provide any external synchronization, then ArrayDeque will not give you synchronization features just like Vector(provides internal features for thread safety-concurrency)

Upvotes: -2

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