Hi,

Anyone can help explain what is the difference between x.atomicOp!"+="(1) and atomicFetchAdd(x, 1)?

From the doc, their return values are different

atomicOp
Performs the binary operation 'op' on val using 'mod' as the modifier.
Returns:
The result of the operation.

atomicFetchAdd
Atomically adds mod to the value referenced by val and returns the value val held previously. This operation is both lock-free and atomic.
Returns:
The value held previously by val.

Apart from this, any other difference, esp in a multithreaded program? Are they the same? Is atomicOp also lock-free?

Thanks.

On Thursday, 10 November 2022 at 17:04:31 UTC, mw wrote:

Looking at the source in druntime, atomicOp!"+=" forwards to atomicFetchAdd internally, so they should have the same behavior.

On Thursday, 10 November 2022 at 18:30:16 UTC, Paul Backus wrote:

Thanks! Indeed:

https://github.com/dlang/dmd/blob/master/druntime/src/core/atomic.d#L582

(source is always your best friend :-)

and looks like atomicFetchAdd is more fundamental:

        return cast(T)(atomicFetchAdd(val, mod) + mod);