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I asked a question on persistence data structure here. After that I came across an article on code project. I have got a question on the following figure from the same article:

enter image description here

The author says:

Inserting a new item into a persistent singly linked list will not alter the existing list but create a new version with the item inserted into it. Instead of copying the entire list and then inserting the item into the copy, a better strategy is to reuse as much of the old list as possible.

Now my doubt wrt to this idea is that since the two versions (Red and Yellow + Red), have common nodes (i.e last three Red nodes), how can one access these two versions simultaneously (for example in a multithreaded application)?

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up vote 3 down vote accepted

Such list is intended to be immutable - the shared nodes will never be written to. There is no problem with several threads reading from the same memory location.

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