• mw (18/18) Nov 10 2022 Hi,
• Paul Backus (4/7) Nov 10 2022 Looking at the source in druntime, `atomicOp!"+="` forwards to
• mw (8/16) Nov 10 2022 Thanks! Indeed:

mw <mingwu gmail.com> writes:

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.

Paul Backus <snarwin gmail.com> writes:

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

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

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

mw <mingwu gmail.com> writes:

On Thursday, 10 November 2022 at 18:30:16 UTC, Paul Backus wrote:
 On Thursday, 10 November 2022 at 17:04:31 UTC, mw wrote:
 Hi,

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

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

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);
```