multithreading - Does Delphi have any equivalent to C's volatile variable?

Question

In C and C++ a variable can be marked as volatile, which means the compiler will not optimize it because it may be modified external to the declaring object. Is there an equivalent in Delphi programming? If not a keyword, maybe a work around?

My thought was to use Absolute, but I wasn't sure, and that may introduce other side effects.

Answer 1

Short answer: no.

However, I am not aware of any situation in which the conservative approach of the compiler will change the number of reads or writes if you follow this approach:

When reading a cross-thread visible location, save its value to a local before doing any further manipulation; similarly, restrict writes to a single assignment.

The Delphi compiler does not perform common subexpression elimination (CSE) on non-local location expressions when there are calls to non-inlined methods between the expressions, as the compiler doesn't do interprocedural optimization and thus it would not be correct even for single-threaded code.

So, you may want to use InterlockedExchange() to do your reads and writes to force this; additionally, this will cause a full memory barrier, so the processor won't reorder reads and writes either.