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CDS C library. The Concurrent Data Structures (CDS) library is a collection of concurrent containers that don't require external (manual) synchronization for shared access, and safe memory reclamation (SMR) algorithms like Hazard Pointer and user-space RCU that is used as an epoch-based SMR. Lock-free programming is a challenge, not just because of the complexity of the task itself, but because of how difficult it can be to penetrate the subject in the first place. I was fortunate in that my first introduction to lock-free (also known as lockless) programming was Bruce Dawson’s.
Active1 year ago
How could I implement this lock-free queue pseudocode in
C
?How would be using the Built-in functions for atomic memory access
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cMinor
cMinorcMinor13.6k6868 gold badges206206 silver badges341341 bronze badges
5 Answers
Public domain, no license, portable implementation of lock-free algorithms in C.
Builds out of the box for Windows and Linux.
Uses GCC on Linux, so uses the intrinsics (well, apart from 128 bit CAS, there's no intrinsic - uses inline assembly for that).
Contains the M&S queue. Have a look at the source code and see how it's done.
user82238
If your goal is production code, simply don't do that; use locks.
In your previous question, you have got enough information explaining why. Correct lock-free implementations of even simple data structures such as queue and stack in the absence of garbage collector are tricky and sophisticated due to the (in)famous ABA problem. Unfortunately some research papers do not take ABA into account for whatever reasons; your pseudo-code seems taken from one of such papers. If you translate it to C and use heap allocated memory for nodes, it will cause undeterministic bugs if used in real code.
If you are doing this stuff to gain experience, then don't expect SO fellows to solve it for you. You have to read all the cited materials and much more, make sure you really understand all nuances of lock-free algorithms such as ABA, study various techniques intended to address the issue, study existing lock-free implementations, etc.
Finally, little guidance for translating the given pseudo-code into C:
q^.value ← x
means q_elem->data = x;
repeat .. until COMPARE&SWAP(head, p, p^.next)
is equivalent to do {..} while (!__sync_bool_compare_and_swap(q_obj->head, q_elem, q_elem->next);
where
q_obj
is an instance of type queue_t
(i.e. a queue) and q_elem
is an instance of type queueelem_t
(i.e. a queue node).Community♦
Alexey KukanovAlexey Kukanov10.5k11 gold badge3030 silver badges5353 bronze badges
While not exactly C, check out the proposed Boost.Lockfree library. The internals are pretty easy to grok and could be ported to C, or, conversely, you could wrap Boost.Lockfree in a C API and use that.
Similarly, Boostcon 2010 had lots of discussion about lockfree programming and STM which is worth looking at if you're interested in this subject. I can't find a link to the videos, but the talks from Intel, IBM and AMD were worth watching since they're dealing with STM at the CPU level.
SeanSean8,05544 gold badges3232 silver badges4040 bronze badges
It sounds like what you want is called an MCS queue lock (although deceptively named, it's really lock-free, just not wait-free), and there is some good pseudo-code available here: http://www.cs.rochester.edu/research/synchronization/pseudocode/ss.html#mcs
mattst88mattst88
I use C to write a minimize lockfree queue implementation.
lfq.
It support many producer, many consumer.
Darkautism NongDarkautism Nong
Not the answer you're looking for? Browse other questions tagged cqueuelock-free or ask your own question.
The Concurrent Data Structures (CDS) library is a collection of concurrent containersthat don't require external (manual) synchronization for shared access, and safe memory reclamation (SMR)algorithms like Hazard Pointerand user-space RCU that is used as an epoch-based SMR.
CDS is mostly header-only template library. Only SMR core implementation is segregated to .so/.dll file.
The library contains the implementations of the following containers:
- lock-free stack with optional elimination support
- several algo for lock-free queue, including classic Michael & Scott algorithm and its derivatives,the flat combining queue, the segmented queue.
- several implementation of unordered set/map - lock-free and fine-grained lock-based
- flat-combining technique
- lock-free skip-list
- lock-free FeldmanHashMap/Set Multi-Level Array Hashwith thread-safe bidirectional iterator support
- Bronson's et al algorithm for fine-grained lock-based AVL tree
Generally, each container has an intrusive and non-intrusive (STL-like) version belonging tocds::intrusive and cds::container namespace respectively.
Version 2.x of the library is written on C++11 and can be compiled by GCC 4.8+, clang 3.6+, Intel C++ 15+,and MS VC++ 14 (2015) and above
Download the latest release from http://sourceforge.net/projects/libcds/files/
See online doxygen-generated doc here: http://libcds.sourceforge.net/doc/cds-api/index.html
Evolution of libcds (Gource visualization by Landon Wilkins): https://www.youtube.com/watch?v=FHaJvVdmJ0w
How to build
- *nix: use CMake
- Windows: use MS Visual C++ 2017 project
Some parts of libcds may depend on DCAS (double-width compare-and-swap) atomic primitive ifthe target architecture supports it. For x86, cmake build script enables
-mcx16
compiler flag thatswitches DCAS support on. You may manually disable DCAS support with the following command line flagsin GCC/clang (for MS VC++ compiler DCAS is not supported):-DCDS_DISABLE_128BIT_ATOMIC
- for 64bit build-DCDS_DISABLE_64BIT_ATOMIC
- for 32bit build
All your projects AND libcds MUST be compiled with the same flags - either with DCAS support or without it.
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Pull request requirements
- Pull-request to master branch will be unconditionally rejected
- integration branch is intended for pull-request. Usually, integration branch is the same as master
- dev branch is intended for main developing. Usually, it contains unstable code
References
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Stack
- TreiberStack: [1986] R. K. Treiber. Systems programming: Coping with parallelism. Technical Report RJ 5118, IBM Almaden Research Center, April 1986.
- Elimination back-off implementation is based on idea from [2004] Danny Hendler, Nir Shavit, Lena Yerushalmi 'A Scalable Lock-free Stack Algorithm'pdf
- FCStack - flat-combining wrapper for std::stack
Queue
- BasketQueue: [2007] Moshe Hoffman, Ori Shalev, Nir Shavit 'The Baskets Queue'pdf
- MSQueue:
- [1998] Maged Michael, Michael Scott 'Simple, fast, and practical non-blocking and blocking concurrent queue algorithms'pdf
- [2002] Maged M.Michael 'Safe memory reclamation for dynamic lock-free objects using atomic reads and writes'pdf
- [2003] Maged M.Michael 'Hazard Pointers: Safe memory reclamation for lock-free objects'pdf
- RWQueue: [1998] Maged Michael, Michael Scott 'Simple, fast, and practical non-blocking and blocking concurrent queue algorithms'pdf
- MoirQueue: [2000] Simon Doherty, Lindsay Groves, Victor Luchangco, Mark Moir 'Formal Verification of a practical lock-free queue algorithm'pdf
- OptimisticQueue: [2008] Edya Ladan-Mozes, Nir Shavit 'An Optimistic Approach to Lock-Free FIFO Queues'pdf
- SegmentedQueue: [2010] Afek, Korland, Yanovsky 'Quasi-Linearizability: relaxed consistency for improved concurrency'pdf
- FCQueue - flat-combining wrapper for std::queue
- VyukovMPMCCycleQueue Dmitry Vyukov (see http://www.1024cores.net)
Deque
- flat-combining deque based on stl::deque
Map, set
- MichaelHashMap: [2002] Maged Michael 'High performance dynamic lock-free hash tables and list-based sets'pdf
- SplitOrderedList: [2003] Ori Shalev, Nir Shavit 'Split-Ordered Lists - Lock-free Resizable Hash Tables'pdf
- StripedMap, StripedSet: [2008] Maurice Herlihy, Nir Shavit 'The Art of Multiprocessor Programming'
- CuckooMap, CuckooSet: [2008] Maurice Herlihy, Nir Shavit 'The Art of Multiprocessor Programming'
- SkipListMap, SkipListSet: [2008] Maurice Herlihy, Nir Shavit 'The Art of Multiprocessor Programming'
- FeldmanHashMap, FeldmanHashSet: [2013] Steven Feldman, Pierre LaBorde, Damian Dechev 'Concurrent Multi-level Arrays:Wait-free Extensible Hash Maps'. Supports thread-safe bidirectional iteratorspdf
Ordered single-linked list
- LazyList: [2005] Steve Heller, Maurice Herlihy, Victor Luchangco, Mark Moir, William N. Scherer III, and Nir Shavit 'A Lazy Concurrent List-Based Set Algorithm'pdf
- MichaelList: [2002] Maged Michael 'High performance dynamic lock-free hash tables and list-based sets'pdf
Priority queue
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- MSPriorityQueue: [1996] G.Hunt, M.Michael, S. Parthasarathy, M.Scott 'An efficient algorithm for concurrent priority queue heaps'pdf
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- EllenBinTree: [2010] F.Ellen, P.Fatourou, E.Ruppert, F.van Breugel 'Non-blocking Binary Search Tree'pdf
- BronsonAVLTreeMap - lock-based fine-grained AVL-tree implementation:[2010] Nathan Bronson, Jared Casper, Hassan Chafi, Kunle Olukotun 'A Practical Concurrent Binary Search Tree'pdf
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- Hazard Pointers
- [2002] Maged M.Michael 'Safe memory reclamation for dynamic lock-free objects using atomic reads and writes'pdf
- [2003] Maged M.Michael 'Hazard Pointers: Safe memory reclamation for lock-free objects'pdf
- [2004] Andrei Alexandrescy, Maged Michael 'Lock-free Data Structures with Hazard Pointers'pdf
- User-space RCU
- [2009] M.Desnoyers 'Low-Impact Operating System Tracing' PhD Thesis,Chapter 6 'User-Level Implementations of Read-Copy Update'pdf
- [2011] M.Desnoyers, P.McKenney, A.Stern, M.Dagenias, J.Walpole 'User-LevelImplementations of Read-Copy Update'pdf
Flat Combining technique
- [2010] Hendler, Incze, Shavit and Tzafrir 'Flat Combining and the Synchronization-Parallelism Tradeoff'pdf