diff options
Diffstat (limited to 'deps/v8/src/builtins/builtins-sharedarraybuffer.cc')
| -rw-r--r-- | deps/v8/src/builtins/builtins-sharedarraybuffer.cc | 24 |
1 files changed, 11 insertions, 13 deletions
diff --git a/deps/v8/src/builtins/builtins-sharedarraybuffer.cc b/deps/v8/src/builtins/builtins-sharedarraybuffer.cc index e6251c9480..f89bc25bdb 100644 --- a/deps/v8/src/builtins/builtins-sharedarraybuffer.cc +++ b/deps/v8/src/builtins/builtins-sharedarraybuffer.cc @@ -25,20 +25,18 @@ namespace internal { // #sec-atomics.islockfree inline bool AtomicIsLockFree(double size) { // According to the standard, 1, 2, and 4 byte atomics are supposed to be - // 'lock free' on every platform. But what exactly does 'lock free' mean? - // For example, on x64 V8 uses a lock prefix to implement the semantics of - // many atomic operations. Is that considered a lock? Probably not. + // 'lock free' on every platform. 'Lock free' means that all possible uses of + // those atomics guarantee forward progress for the agent cluster (i.e. all + // threads in contrast with a single thread). // - // On the other hand, V8 emits a few instructions for some arm atomics which - // do appear to be a low level form of a spin lock. With an abundance of - // caution, we only claim to have 'true lock free' support for 8 byte sizes - // on x64 platforms. If people care about this function returning true, then - // we need to clarify exactly what 'lock free' means at the standard level. - bool is_lock_free = size == 1 || size == 2 || size == 4; -#if V8_TARGET_ARCH_x64 - is_lock_free |= size == 8; -#endif - return is_lock_free; + // This property is often, but not always, aligned with whether atomic + // accesses are implemented with software locks such as mutexes. + // + // V8 has lock free atomics for all sizes on all supported first-class + // architectures: ia32, x64, ARM32 variants, and ARM64. Further, this property + // is depended upon by WebAssembly, which prescribes that all atomic accesses + // are always lock free. + return size == 1 || size == 2 || size == 4 || size == 8; } // ES #sec-atomics.islockfree |