Re: [patch libstdc++] Optimize synchronization in std::future if futexes are available.

[Doug Gilmore <Doug.Gilmore@imgtec.com>]

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On 01/18/2015 05:19 AM, Jonathan Wakely wrote:
> On 17/01/15 19:51 -0700, Sandra Loosemore wrote:
>> On 01/17/2015 03:58 PM, Jonathan Wakely wrote:
>>>
>>> My fault, this additional chunk is needed alongside the patch I sent
>>> earlier:
>>>
>>> --- a/libstdc++-v3/include/bits/atomic_futex.h
>>> +++ b/libstdc++-v3/include/bits/atomic_futex.h
>>> @@ -35,7 +35,7 @@
>>> #include <bits/c++config.h>
>>> #include <atomic>
>>> #include <chrono>
>>> -#if !defined(_GLIBCXX_HAVE_LINUX_FUTEX)
>>> +#if ! (defined(_GLIBCXX_HAVE_LINUX_FUTEX) && ATOMIC_INT_LOCK_FREE > 1)
>>> #include <mutex>
>>> #include <condition_variable>
>>> #endif
>>>
>>> What I sent earlier causes your target to use std::mutex and
>>> std::condition_variable, but without the bit above the headers aren't
>>> included.
>>
>> Still no joy:
>> /scratch/sandra/arm-fsf2/src/gcc-mainline/libstdc++-v3/src/c++11/futex.cc:45:3: error: '__atomic_futex_unsigned_base' has not been declared
>>   __atomic_futex_unsigned_base::_M_futex_wait_until(unsigned *__addr,
>>   ^
>> /scratch/sandra/arm-fsf2/src/gcc-mainline/libstdc++-v3/src/c++11/futex.cc:88:3: error: '__atomic_futex_unsigned_base' has not been declared
>>   __atomic_futex_unsigned_base::_M_futex_notify_all(unsigned* __addr)
>>   ^
> 
> futex.cc needs the same change ...
I am still noticing a problem building a native X86_64 ToT compiler on
Ubuntu 12.04.5 LTS.

Attached is a patch where the CPP guards in atomic_futex.h are
reflected in futex.cc, which fixes my build problem.

OK to commit?

Thanks,

Doug


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From 1debe13da342ac30d905e12a9ca243e30cb61870 Mon Sep 17 00:00:00 2001
From: Doug Gilmore <doug.gilmore@imgtec.com>
Date: Wed, 28 Jan 2015 14:29:14 -0800
Subject: [PATCH] CPP guards in futex.cc should match guards in futex.ii.

---
 libstdc++-v3/src/c++11/futex.cc |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/libstdc++-v3/src/c++11/futex.cc b/libstdc++-v3/src/c++11/futex.cc
index 1336779..5087483 100644
--- a/libstdc++-v3/src/c++11/futex.cc
+++ b/libstdc++-v3/src/c++11/futex.cc
@@ -23,6 +23,7 @@
 // <http://www.gnu.org/licenses/>.
 
 #include <bits/atomic_futex.h>
+#if defined(_GLIBCXX_HAS_GTHREADS) && defined(_GLIBCXX_USE_C99_STDINT_TR1)
 #if defined(_GLIBCXX_HAVE_LINUX_FUTEX) && ATOMIC_INT_LOCK_FREE > 1
 #include <chrono>
 #include <climits>
@@ -93,4 +94,5 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   }
 
 }
-#endif
+#endif // _GLIBCXX_HAVE_LINUX_FUTEX && ATOMIC_INT_LOCK_FREE > 1
+#endif // _GLIBCXX_HAS_GTHREADS && _GLIBCXX_USE_C99_STDINT_TR1
-- 
1.7.9.5