Is ‘volatile’ needed in this multi-threaded C++ code?

by

You should not depend on volatile to guarantee thread safety, this is because even though the compiler will guarantee that the the variable is always read from memory (and not a register cache), in multi-processor environments a memory barrier will also be required.

Rather use the correct lock around the shared memory. Locks like a Critical Section are often extremely lightweight and in a case of no contention will probably be all implemented userside. They will also contain the necessary memory barriers.

Volatile should only be used for memory mapped IO where multiple reads may return different values. Similarly for memory mapped writes.

More Related Contents:

  1. When to use volatile with multi threading?
  2. Why is volatile not considered useful in multithreaded C or C++ programming?
  3. Does the C++ volatile keyword introduce a memory fence?
  4. Is volatile bool for thread control considered wrong?
  5. Simple example of threading in C++
  6. Concurrency: Atomic and volatile in C++11 memory model
  7. Programmatically find the number of cores on a machine
  8. How can I implement ABA counter with c++11 CAS?
  9. Multithreading program stuck in optimized mode but runs normally in -O0
  10. Using stdlib’s rand() from multiple threads
  11. Lock-free Progress Guarantees in a circular buffer queue
  12. What are the correct link options to use std::thread in GCC under linux?
  13. Are C++ Reads and Writes of an int Atomic?
  14. When should I use _mm_sfence _mm_lfence and _mm_mfence
  15. How to efficiently display OpenCV video in Qt?
  16. What’s the difference between “static” and “dynamic” schedule in OpenMP?
  17. Does Interlocked.CompareExchange use a memory barrier?
  18. Precise thread sleep needed. Max 1ms error
  19. Why does std::cout convert volatile pointers to bool?
  20. Which std::async implementations use thread pools?
  21. What is the difference between packaged_task and async
  22. Thread safe lazy construction of a singleton in C++
  23. Is it ok to read a shared boolean flag without locking it when another thread may set it (at most once)?
  24. c++ work queues with blocking
  25. Is C++ static member variable initialization thread-safe?
  26. C++ – std::thread crashes upon execution
  27. Understanding std::atomic::compare_exchange_weak() in C++11
  28. Is it allowed for a compiler to optimize away a local volatile variable?
  29. What Rules does compiler have to follow when dealing with volatile memory locations?
  30. Loading a dll from a dll?

Leave a Comment