Re: RFR 8161444 VarHandles should provide access bitwise atomics

[Paul Sandoz]

Hi,

I updated the webrev in place.

The doc of each bitwise access mode now includes:

* <p>If the variable type is the non-integral {@code boolean} type then a
* logical OR is performed instead of a bitwise OR.

The unsafe bitwise acquire CAS methods have:

@ForceInline
public final int getAndBitwiseOrIntAcquire(Object o, long offset, int mask) {
    int current;
    do {
        // Plain read, the value is a hint, the acquire CAS does the work
        current = getInt(o, offset);
    } while (!weakCompareAndSwapIntAcquire(o, offset,
                                           current, current | mask));
    return current;
}

Thanks,
Paul.

> On 9 Aug 2016, at 17:14, Paul Sandoz <paul.san...@oracle.com> wrote:
> 
> Hi
> 
> Please review the following webrev which combines:
> 
>  8161444 VarHandles should provide access bitwise atomics
>  8162107 Add acquire/release variants for getAndSet and getAndAdd
> 
>  
> http://cr.openjdk.java.net/~psandoz/jdk9/JDK-8161444-vhs-bitwise-atomics/webrev/
>  
> http://cr.openjdk.java.net/~psandoz/jdk9/JDK-8161444-vhs-bitwise-atomics/specdiff/overview-summary.html
> 
> The set of access modes are expanded for support bitwise or/and/xor 
> operations for volatile/acquire/release. Acquire/release getAndAdd and 
> getAndSet access modes are also added (a future webrev will remove 
> getAndAdd). This gets closer to parity with C++ atomics.
> 
> As a follow on i will:
> 
> - update the Hotspot Unsafe tests as a separate issue (the VarHandle tests 
> implicitly test the Unsafe methods).
> 
> - log HotSpot bugs for making the Unsafe bitwise atomics intrinsic for 
> various platforms.
> 
> Thanks,
> Paul.