Despite my pathological distrust of spin locks, the number just don't lie. I've put a small spin in __sp_mut::lock() on std::mutex::try_lock(), which is testing quite well. In my experience, putting in a yield for every failed iteration is also a major performance booster. This change makes one of the performance tests I was using (a highly contended one) run about 20 times faster.
git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@160967 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/src/memory.cpp b/src/memory.cpp
index 7caab26..1c108b8 100644
--- a/src/memory.cpp
+++ b/src/memory.cpp
@@ -10,6 +10,7 @@
#define _LIBCPP_BUILDING_MEMORY
#include "memory"
#include "mutex"
+#include "thread"
_LIBCPP_BEGIN_NAMESPACE_STD
@@ -129,13 +130,23 @@
void
__sp_mut::lock() _NOEXCEPT
{
- reinterpret_cast<mutex*>(_)->lock();
+ mutex& m = *static_cast<mutex*>(_);
+ unsigned count = 0;
+ while (!m.try_lock())
+ {
+ if (++count > 16)
+ {
+ m.lock();
+ break;
+ }
+ this_thread::yield();
+ }
}
void
__sp_mut::unlock() _NOEXCEPT
{
- reinterpret_cast<mutex*>(_)->unlock();
+ static_cast<mutex*>(_)->unlock();
}
__sp_mut&