* [committed] libstdc++: Relax memory ordering for default memory resource object
@ 2022-05-17 19:56 Jonathan Wakely
0 siblings, 0 replies; only message in thread
From: Jonathan Wakely @ 2022-05-17 19:56 UTC (permalink / raw)
To: libstdc++, gcc-patches; +Cc: Thomas Rodgers
Tested powerpc64le-linux, pushed to trunk.
-- >8 --
Currently pmr::set_default_resource and pmr::get_default_resource both
use sequentially consistent memory ordering. This is overkill. The
standard only requires that a call to set_default_resource synchronizes
with subsequent calls to set_default_resource and get_default_resource.
Using acquire-release for the setter and acquire for the getter is
sufficient to meet the requirement.
Reviewed-by: Thomas Rodgers <trodgers@redhat.com>
libstdc++-v3/ChangeLog:
* src/c++17/memory_resource.cc (set_default_resource): Use
memory_order_acq_rel.
(get_default_resource): Use memory_order_acquire.
---
libstdc++-v3/src/c++17/memory_resource.cc | 12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)
diff --git a/libstdc++-v3/src/c++17/memory_resource.cc b/libstdc++-v3/src/c++17/memory_resource.cc
index bb6334c9694..8bc55a69f1f 100644
--- a/libstdc++-v3/src/c++17/memory_resource.cc
+++ b/libstdc++-v3/src/c++17/memory_resource.cc
@@ -112,13 +112,13 @@ namespace pmr
mutex mx;
memory_resource* val;
- memory_resource* load()
+ memory_resource* load(std::memory_order)
{
lock_guard<mutex> lock(mx);
return val;
}
- memory_resource* exchange(memory_resource* r)
+ memory_resource* exchange(memory_resource* r, std::memory_order)
{
lock_guard<mutex> lock(mx);
return std::__exchange(val, r);
@@ -134,12 +134,12 @@ namespace pmr
memory_resource* val;
- memory_resource* load() const
+ memory_resource* load(std::memory_order) const
{
return val;
}
- memory_resource* exchange(memory_resource* r)
+ memory_resource* exchange(memory_resource* r, std::memory_order)
{
return std::__exchange(val, r);
}
@@ -166,12 +166,12 @@ namespace pmr
{
if (r == nullptr)
r = new_delete_resource();
- return default_res.obj.exchange(r);
+ return default_res.obj.exchange(r, std::memory_order_acq_rel);
}
memory_resource*
get_default_resource() noexcept
- { return default_res.obj.load(); }
+ { return default_res.obj.load(std::memory_order_acquire); }
// Member functions for std::pmr::monotonic_buffer_resource
--
2.34.3
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2022-05-17 19:56 [committed] libstdc++: Relax memory ordering for default memory resource object Jonathan Wakely
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