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

[Dan Albert]

Howard, it looks like you're the one that added the commented out behavior,
and your commit said that you "could not yet do that". Any update?

- Dan


On Tue, May 6, 2014 at 3:35 PM, Dan Albert <danalbert at google.com> wrote:

> 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
>>
>>
>
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