Either not returning *this, or in the case of Variant, not checking for
self assignment. In AK::Atomic, we can't return *this due to the wrapper
semantics Atomic implements.
Note: this exact implementation is needed for __atomic_is_lock_free to
link with both GCC (for the SerenityOS build) and Clang (for the Fuzzer
build). The size argument must be a compile-time constant, otherwise it
fails to link with both compilers. Alternatively, the following
definition links with GCC but fails with Clang:
template<size_t S>
static inline bool atomic_is_lock_free(volatile void* ptr = nullptr)
{
return __atomic_is_lock_free(S, ptr);
}
While Clang claims to implement GCC's atomics libcall API, a small
incompatibility caused our builds to fail on Clang.
Clang requires requires the operands to its fixed-size functions to be
integer types, while GCC will take any type with the same size and
alignment as the various integer primitives. This was problematic, as
atomic `enum class`es would not compile.
Furthermore, Clang does not like if only one operand pointer is marked
volatile. Because it only affects the standalone atomic functions, that
will be fixed in a later commit.
As an added benefit, the code is more type-safe, as it won't let us
perform arithmetic on non-integer types. Types with overloaded
arithmetic types won't cause unexpected behavior anymore.
The constructors for the various atomic types can now be used in
constant expressions.
SPDX License Identifiers are a more compact / standardized
way of representing file license information.
See: https://spdx.dev/resources/use/#identifiers
This was done with the `ambr` search and replace tool.
ambr --no-parent-ignore --key-from-file --rep-from-file key.txt rep.txt *
This commit makes the user-facing StdLibExtras templates and utilities
arguably more nice-looking by removing the need to reach into the
wrapper structs generated by them to get the value/type needed.
The C++ standard library had to invent `_v` and `_t` variants (likely
because of backwards compat), but we don't need to cater to any codebase
except our own, so might as well have good things for free. :^)
We use atomic_signal_fence and atomic_thread_fence together to prevent
reordering of memory accesses by the CPU and the compiler.
The usage of these functions was suggested by @tomuta so we can be sure
that important memory accesses happen in the expected order :)
This is useful for collecting statistics, e.g.
Atomic<unsigned, MemoryOrder::memory_order_relaxed> would allow
using operators such as ++ to use relaxed semantics throughout
without having to explicitly call fetch_add with the memory order.
As suggested by Joshua, this commit adds the 2-clause BSD license as a
comment block to the top of every source file.
For the first pass, I've just added myself for simplicity. I encourage
everyone to add themselves as copyright holders of any file they've
added or modified in some significant way. If I've added myself in
error somewhere, feel free to replace it with the appropriate copyright
holder instead.
Going forward, all new source files should include a license header.
