The idiomatic way to modify two variables atomically is to use a lock. You can’t do it for std::unique_ptr without a lock. Even std::atomic<int> doesn’t provide a way to swap two values atomically. You can update one atomically and get its previous value back, but a swap is conceptually three steps, in terms of the … Read more
Beyond the simple cases of the InterlockedXxx functions, it seems like the prevailing pattern with all of these is that they implement their own locks. None of the answers here really seem to get to the heart of the difference between a “lock-free” CAS loop and a mutex or spin-lock. The important difference is that … Read more
I’m a firm believer in that if you’re using interlocked to increment shared data, then you should use interlocked everywhere you access that shared data. Likewise, if you use insert you favorite synchronization primitive here to increment shared data, then you should use insert you favorite synchronization primitive here everywhere you access that shared data. … Read more
Here is an article over at software.intel.com on that sheds little light on user level locks: User level locks involve utilizing the atomic instructions of processor to atomically update a memory space. The atomic instructions involve utilizing a lock prefix on the instruction and having the destination operand assigned to a memory address. The following … Read more
I’ve made a particular study of lock-free data structures in the last couple of years. I’ve read most of the papers in the field (there’s only about fourty or so – although only about ten or fifteen are any real use 🙂 AFAIK, a lock-free circular buffer has not been invented. The problem will be … Read more
As of 1.53, boost provides a set of lock free data structures, including queues, stacks and single-producer/single-consumer queues (i.e. ring buffers).
Current “lock-free” implementations follow the same pattern most of the time: read some state and make a copy of it* modify copy* do an interlocked operation retry if it fails (*optional: depends on the data structure/algorithm) The last bit is eerily similar to a spinlock. In fact, it is a basic spinlock. 🙂 I agree … Read more
I have looked for actual data for the past days, and found nothing. However, I did some research, which compares the cost of atomic ops with the costs of cache misses. The cost of the x86 LOCK prefix, (including lock cmpxchg for atomic CAS), before PentiumPro (as described in the doc), is a memory access … Read more