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Asked: 2026-06-05T01:36:19+00:00

I am planning to do the following: store a deque of pre-built objects to

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I am planning to do the following:

store a deque of pre-built objects to be consumed. The main thread might consume these objects here and there. I have another junky thread used for logging and other not time-critical but expensive things. When the pre-built objects are running low, I will refill them in the junky thread.

Now my question is, is there going to be race condition here? Technically one thread is consuming objects from the front, and another thread is pushing objects into the back. As long as I don’t let the size run down to zero, it should be fine. The only thing that concerns me is the “size” of this deque. Do they store a integer “size” variable in STL containers? should modifying that size variable introduce race conditions?

What’s the best way of solving this problem? I don’t really want to use locks, because the main thread is performance critical (the reason I pre-built these objects in the first place!)

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1 Answer

  1. Editorial Team

    Another option would be to have 2 deques, one for read another for write. The main thread reads, and the other writes. When the read deque is empty, switch the deques (just move 2 pointers), which would involve a lock, but only occasionally.

    The consumer thread would drive the switch so it would only need to do a lock when switching. The producer thread would need to lock per write in case the switch happens in the middle of a write, but as you mention the consumer is less performance-critical, so no worries there.

    What you’re suggesting regarding no locks is indeed dangerous as others mention.

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