'Why is volatile deprecated in C++20?

According to cppreference, most uses of the volatile keyword are to be deprecated in C++20. What is the disadvantage of volatile? And what is the alternative solution when not using volatile?

c++volatilec++20


Solution 1:[1]

There's a good talk by the C++ committee language evolution chair on why.

Brief summary, the places that volatile is being removed from didn't have any well defined meaning in the standard and just caused confusion.

Motivating (Ambiguous) Examples

  • Volatile bit Fields should be specified by your hardware manual and/or compiler.
  • Is += a single/atomic instruction? How about ++?
  • How many reads/writes are needed for compare_exchange? What if it fails?
  • What does void foo(int volatile n) mean? or int volatile foo()?
  • Should *vp; do a load? (This has changed twice in the standard.)

Threading

Historically, people have used volatile to achieve thread safety in C and C++. In C++11, non-UB ways to create synchronization and shared state between threads were added. I recommend Back to Basics: Concurrency as a good introduction.

Sources

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Source: Stack Overflow

Solution Source
Solution 1 Clifford

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