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

Message ID 20150118131915.GY3360@redhat.com
State New
Headers show

Commit Message

Jonathan Wakely Jan. 18, 2015, 1:19 p.m. UTC 
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 ...
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Patch

diff --git a/libstdc++-v3/src/c++11/futex.cc b/libstdc++-v3/src/c++11/futex.cc
index ad766c8..f24b44e 100644
--- a/libstdc++-v3/src/c++11/futex.cc
+++ b/libstdc++-v3/src/c++11/futex.cc
@@ -23,7 +23,7 @@ 
 // <http://www.gnu.org/licenses/>.
 
 #include <bits/c++config.h>
-#if defined(_GLIBCXX_HAVE_LINUX_FUTEX)
+#if defined(_GLIBCXX_HAVE_LINUX_FUTEX) && ATOMIC_INT_LOCK_FREE > 1
 #include <bits/atomic_futex.h>
 #include <chrono>
 #include <climits>