[cfe-dev] [PATCH] Replaces __sync_swap with std::atomic

[Dan Albert]

I don't know if these were left commented out because they don't work on
some platforms, but they work on OS X. Were they left commented out because
they had been forgotten?

- Dan

On Tue, May 6, 2014 at 3:32 PM, Dan Albert <danalbert at google.com> wrote:

> The commented out regions mentioning this worked as is.
> ---
>  src/cxa_default_handlers.cpp | 16 ++++------------
>  src/cxa_handlers.cpp         | 23 +++++------------------
>  src/cxa_handlers.hpp         | 27 +++++----------------------
>  3 files changed, 14 insertions(+), 52 deletions(-)
>
> diff --git a/src/cxa_default_handlers.cpp b/src/cxa_default_handlers.cpp
> index 27ffb71..6a48cd9 100644
> --- a/src/cxa_default_handlers.cpp
> +++ b/src/cxa_default_handlers.cpp
> @@ -87,12 +87,8 @@ static void default_unexpected_handler()
>  //
>  // Global variables that hold the pointers to the current handler
>  //
> -std::terminate_handler  __cxa_terminate_handler =
> default_terminate_handler;
> -std::unexpected_handler __cxa_unexpected_handler =
> default_unexpected_handler;
> -
> -// In the future these will become:
> -// std::atomic<std::terminate_handler>
>  __cxa_terminate_handler(default_terminate_handler);
> -// std::atomic<std::unexpected_handler>
> __cxa_unexpected_handler(default_unexpected_handler);
> +std::atomic<std::terminate_handler>
>  __cxa_terminate_handler(default_terminate_handler);
> +std::atomic<std::unexpected_handler>
> __cxa_unexpected_handler(default_unexpected_handler);
>
>  namespace std
>  {
> @@ -102,9 +98,7 @@ set_unexpected(unexpected_handler func) _NOEXCEPT
>  {
>         if (func == 0)
>                 func = default_unexpected_handler;
> -       return __sync_swap(&__cxa_unexpected_handler, func);
> -//  Using of C++11 atomics this should be rewritten
> -//  return __cxa_unexpected_handler.exchange(func, memory_order_acq_rel);
> +       return __cxa_unexpected_handler.exchange(func,
> memory_order_acq_rel);
>  }
>
>  terminate_handler
> @@ -112,9 +106,7 @@ set_terminate(terminate_handler func) _NOEXCEPT
>  {
>         if (func == 0)
>                 func = default_terminate_handler;
> -       return __sync_swap(&__cxa_terminate_handler, func);
> -//  Using of C++11 atomics this should be rewritten
> -//  return __cxa_terminate_handler.exchange(func, memory_order_acq_rel);
> +       return __cxa_terminate_handler.exchange(func,
> memory_order_acq_rel);
>  }
>
>  }
> diff --git a/src/cxa_handlers.cpp b/src/cxa_handlers.cpp
> index 6c13fcd..2d1682e 100644
> --- a/src/cxa_handlers.cpp
> +++ b/src/cxa_handlers.cpp
> @@ -25,10 +25,7 @@ namespace std
>  unexpected_handler
>  get_unexpected() _NOEXCEPT
>  {
> -    return __sync_fetch_and_add(&__cxa_unexpected_handler,
> (unexpected_handler)0);
> -//  The above is safe but overkill on x86
> -//  Using of C++11 atomics this should be rewritten
> -//  return __cxa_unexpected_handler.load(memory_order_acq);
> +       return __cxa_unexpected_handler.load(memory_order_acquire);
>  }
>
>  __attribute__((visibility("hidden"), noreturn))
> @@ -50,10 +47,7 @@ unexpected()
>  terminate_handler
>  get_terminate() _NOEXCEPT
>  {
> -    return __sync_fetch_and_add(&__cxa_terminate_handler,
> (terminate_handler)0);
> -//  The above is safe but overkill on x86
> -//  Using of C++11 atomics this should be rewritten
> -//  return __cxa_terminate_handler.load(memory_order_acq);
> +       return __cxa_terminate_handler.load(memory_order_acquire);
>  }
>
>  __attribute__((visibility("hidden"), noreturn))
> @@ -101,25 +95,18 @@ terminate() _NOEXCEPT
>      __terminate(get_terminate());
>  }
>
> -extern "C" new_handler __cxa_new_handler = 0;
> -// In the future these will become:
> -// std::atomic<std::new_handler>  __cxa_new_handler(0);
> +std::atomic<std::new_handler>  __cxa_new_handler(0);
>
>  new_handler
>  set_new_handler(new_handler handler) _NOEXCEPT
>  {
> -    return __sync_swap(&__cxa_new_handler, handler);
> -//  Using of C++11 atomics this should be rewritten
> -//  return __cxa_new_handler.exchange(handler, memory_order_acq_rel);
> +       return __cxa_new_handler.exchange(handler, memory_order_acq_rel);
>  }
>
>  new_handler
>  get_new_handler() _NOEXCEPT
>  {
> -    return __sync_fetch_and_add(&__cxa_new_handler, (new_handler)0);
> -//  The above is safe but overkill on x86
> -//  Using of C++11 atomics this should be rewritten
> -//  return __cxa_new_handler.load(memory_order_acq);
> +       return __cxa_new_handler.load(memory_order_acquire);
>  }
>
>  }  // std
> diff --git a/src/cxa_handlers.hpp b/src/cxa_handlers.hpp
> index ce567ec..23669fe 100644
> --- a/src/cxa_handlers.hpp
> +++ b/src/cxa_handlers.hpp
> @@ -13,7 +13,9 @@
>  #ifndef _CXA_HANDLERS_H
>  #define _CXA_HANDLERS_H
>
> +#include <atomic>
>  #include <exception>
> +#include <new>
>
>  namespace std
>  {
> @@ -28,27 +30,8 @@ __terminate(terminate_handler func) _NOEXCEPT;
>
>  }  // std
>
> -extern "C"
> -{
> -
> -extern void (*__cxa_terminate_handler)();
> -extern void (*__cxa_unexpected_handler)();
> -extern void (*__cxa_new_handler)();
> -
> -/*
> -
> -    At some point in the future these three symbols will become
> -    C++11 atomic variables:
> -
> -    extern std::atomic<std::terminate_handler>  __cxa_terminate_handler;
> -    extern std::atomic<std::unexpected_handler> __cxa_unexpected_handler;
> -    extern std::atomic<std::new_handler>        __cxa_new_handler;
> -
> -    This change will not impact their ABI.  But it will allow for a
> -    portable performance optimization.
> -
> -*/
> -
> -} // extern "C"
> +extern std::atomic<std::terminate_handler>  __cxa_terminate_handler;
> +extern std::atomic<std::unexpected_handler> __cxa_unexpected_handler;
> +extern std::atomic<std::new_handler>        __cxa_new_handler;
>
>  #endif  // _CXA_HANDLERS_H
> --
> 1.9.2
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/cfe-dev/attachments/20140506/228bd4fa/attachment.html>