Actually you could. Atomic CAS instructions support up to 64bits on a 32bit platform, and 128bits on a 64bit platform. As long as those are aligned and side-by-side, you can change both atomically. Although Boost does not currently do this.
Right, but the assignment operator doesn't *only* store those two values. Like I detailed elsewhere, it would need to initialize a temporary, do the double-wide swap of that with the LHS, and then let the temp go out of scope. The instruction is CMPXCHG8B (or -16B on x64), which as you point out also does a compare. So code a read followed by the cmp-and-swap. Checking the CPU manual, I also see that in x64 the operand must be aligned on a 16-byte boundary. The compiler will only align the structure on the 8-byte boundary (each field is an 8-byte pointer), so you'll also have to convince the compiler to align the structure more strictly. That doesn't seem to be necessary in x86 mode. TradeStation Group, Inc. is a publicly-traded holding company (NASDAQ GS: TRAD) of three operating subsidiaries, TradeStation Securities, Inc. (Member NYSE, FINRA, SIPC and NFA), TradeStation Technologies, Inc., a trading software and subscription company, and TradeStation Europe Limited, a United Kingdom, FSA-authorized introducing brokerage firm. None of these companies provides trading or investment advice, recommendations or endorsements of any kind. The information transmitted is intended only for the person or entity to which it is addressed and may contain confidential and/or privileged material. Any review, retransmission, dissemination or other use of, or taking of any action in reliance upon, this information by persons or entities other than the intended recipient is prohibited. If you received this in error, please contact the sender and delete the material from any computer.