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Asked: 2026-05-27T02:18:12+00:00

This is about thread safety of std::map . Now, simultaneous reads are thread-safe but

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This is about thread safety of std::map. Now, simultaneous reads are thread-safe but writes are not. My question is that if I add unique element to the map everytime, will that be thread-safe?

  1. So, for an example, If I have a map like this std:map<int, std::string> myMap
    and I always add new keys and never modify the existing key-value, will that be thread-safe?

  2. More importantly, will that give me any random run-time behavior?

  3. Is adding new keys also considered modification? If the keys are always different while adding, shouldn’t it be thread-safe as it modifies an independent part of the memory?

Thanks
Shiv

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1 Answer

  1. Editorial Team

    1) Of course not

    2) Yes, I hope you’ll encounter it during testing, not later

    3) Yes, it is. The new element is added in a different location, but many pointers are modified during that.

    The map is implemented by some sort of tree in most if not all implementations. Inserting a new element in a tree modifies it by rearranging nodes by means of resetting pointers to point to different nodes. So it is not thread safe

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