STL vector and thread-safety

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I want to ask whether a problem may occur during reallocating of vector to a larger memory block, if there are some child working threads left from the previous update.

Yes, this would be very bad.

If you are using a container from multiple threads and at least one thread may perform some action that may modify the state of the container, access to the container must be synchronized.

In the case of std::vector, anything that changes its size (notably, insertions and erasures) change its state, even if a reallocation is not required (any insertion or erasure requires std::vector‘s internal size bookkeeping data to be updated).

One solution to your problem would be to have the producer dynamically allocate the std::vector and use a std::shared_ptr<std::vector<T> > to own it and give this std::shared_ptr to each of the consumers.

When the producer needs to add more data, it can dynamically allocate a new std::vector with a new, larger size and copies of the elements from the old std::vector. Then, when you spin off new consumers or update consumers with the new data, you simply need to give them a std::shared_ptr to the new std::vector.

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