* Regenerate code to update copyright end year to 2023
* Test behaviour of default values initialized in different ways
This adds repro tests for #126 and #129
* Fix Swap and CompareAndSwap for Value wrappers
Fixes#126, #129
All atomic types can be used without initialization, e.g., `var v
<AtomicType>`. This works fine for integer types as the initialized
value of 0 matches the default value for the user-facing type. However,
for Value wrappers, they are initialized to `nil`, which is a value that
can't be set (triggers a panic) so the default value for the user-facing
type is forced to be stored as a different value. This leads to multiple
possible values representing the default user-facing type.
E.g., an `atomic.String` with value `""` may be represented by the
underlying atomic as either `nil`, or `""`. This causes issues when we
don't handle the `nil` value correctly, causing to panics in `Swap` and
incorrectly not swapping values in `CompareAndSwap`.
This change fixes the above issues by:
* Requiring `pack` and `unpack` function in gen-atomicwrapper as the
only place we weren't supplying them was for `String`, and the
branching adds unnecessary complexity, especially with added `nil`
handling.
* Extending `CompareAndSwap` for `Value` wrappers to try an additional
`CompareAndSwap(nil, <new>)` only if the original `CompareAndSwap`
fails and the old value is the zero value.
Adds CompareAndSwap and Swap methods to String, Error, and Value,
implemented by making use of Value.CompareAndSwap and Value.Swap
added in Go 1.17.
Following that, add CompareAndSwap to all other types with "CAS" methods
and deprecate CAS in favor of CompareAndSwap, since that's the convention
the standard library chose for these in Go 1.19.
This change is a renaming with no functional changes.
It includes the following renames:
* `val` for arguments that replace the atomic value (e.g., `Store`).
* `delta` for arguments that offset the atomic value (e.g., `Add`).
* `old`, `new` for arguments to `CAS`.
* `old` named return from `Swap`.
* `swapped` for named return from `CAS`.
This also matches the names used in the stdlib atomic interface:
https://golang.org/pkg/sync/atomic/
The generators gen-atomicint and gen-atomicwrapper hard-coded the year
into the licenses of the generated files.
Update to generate year ranges for the licenses, starting at 2020, going
to whatever today's year is.
The embedded `nocmp` field and other similar fields are unused in tests
and the rest of our code.
We can get the effect of `nocmp` without embedding the fields by using
`_ nocmp` as a field.
Add safe `String()` methods for atomic types that replicate the same
behavior as `fmt.Sprintf("%v", x.Load())` without the allocations.
As with json.Marshaler/Unmarshaler, we've omitted the `atomic.Value`
type for now.
Resolves#50
It is currently possible to make non-atomic comparisons of atomic
values:
x := atomic.NewInt32(1)
y := atomic.NewInt32(1)
fmt.Println(*x == *y)
This is undesirable because it loads the value in a non-atomic way. The
correct method is,
x := atomic.NewInt32(1)
y := atomic.NewInt32(1)
fmt.Println(x.Load() == y.Load())
To prevent this, disallow comparison of atomic values by embedding an
uncomparable array into atomics. The empty array adds no runtime cost,
and does not increase the in-memory size of the structs. Inspired by
[go4.org/mem#RO][1].
[1]: 3dbcd07079/mem.go (L42)
Note that the Value struct, which embeds `"sync/atomic".Value` was also
changed. This will break usages in the following form, but that's
acceptable because unkeyed struct literals are among the exceptions
stated in the [Go 1 compatibility expectations][2].
import (
syncatomic "sync/atomic"
"go.uber.org/atomic"
)
atomic.Value{syncatomic.Value{..}}
[2]: https://golang.org/doc/go1compat#expectationsResolves#72
Generated files should contain the following comment in the first few
lines for them to be considered generated by GitHub.
Code generated by <executable>
The additional `@generated` tag does the same for Phabricator.
Rather than hand-writing the atomic integers, generate them
automatically from the same template. The generator is at
internal/gen-atomicint.
To ensure these are never out of date, add another `make` target which
verifies that the working tree is left unchanged after regenerating
code.
In anticipation of automatically generating these definitions, pull the
definitions of the various integer types into their own files as well as
their tests.
This will make it easier to review the changes when each of these files
is generated independently and automatically.
