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I'm currently reading C++ Concurrency in Action book by Anthony Williams and there are several lock free data structures implementations. In the forward of the chapter about lock free data structures in the book Anthony is writing:
This brings us to another downside of lock-free and wait-free code: although it can increase the potential for concurrency of operations on a data structure and reduce the time an individual thread spends waiting, it may well decrease overall performance.
And indeed I tested all lock free stack implementations described in the book against lock based implementation from one of the previous chapters. And it seems the performance of lock free code is always lower than the lock based stack.
In what circumstances lock free data structure are more optimal and must be preferred?
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The lock- free mode is almost as fast as blocking mode under almost all workloads, and significantly faster when threads are over- subscribed (more threads than processors). We also compare with several existing lock-based and lock-free alternatives. CCS Concepts: • Theory of computation → Concurrent algorithms.
Lock-Free queues provides us better performance for concurrent queue which is non-blocking and linearizable. Although it introduces ABA problem, we have some workaround solutions for it. In general, if if don't want to lock your queue in concurrent programming, try lock-free queue algorithm.
With a lock-free data structure, some thread makes progress with every step. With a wait-free data structure, every thread can make forward progress, regardless of what the other threads are doing; there's no need for waiting. This is a desirable property to have but hard to achieve.
A lock-free data structure can be used to improve performance. A lock-free data structure increases the amount of time spent in parallel execution rather than serial execution, improving performance on a multi-core processor, because access to the shared data structure does not need to be serialized to stay coherent.
One benefit of lock-free structures is that they do not require context switch. However, in modern systems, uncontended locks are also context-switch free. To benefit (performance-wise) from lock-free algo, several conditions have to be met:
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