This defines __platform_wait, __platform_notify, and
__platform_wait_until for FreeBSD, making use of the _umtx_op syscall.
The Linux versions of those functions only support 32-bit integers, but
the FreeBSD versions use the syscall for both 32-bit and 64-bit types,
as the _umtx_op supports both.
libstdc++-v3/ChangeLog:
PR libstdc++/120527
* include/bits/atomic_wait.h [__FreeBSD__] (__platform_wait_t):
Define typedef.
[__FreeBSD__] (__platform_wait_uses_type): Define variable
template.
* src/c++20/atomic.cc [__FreeBSD__] (_GLIBCXX_HAVE_PLATFORM_WAIT)
(__platform_wait, __platform_notify, __platform_wait_until):
Define.
(__platform_load): Define.
---
v4: Tomasz noticed that __spin_impl assumes the waitable is always a
__platform_wait_t, but the FreeBSD patch enables the fast path for both
32-bit and 64-bit integers, so we need to adjust how __spin_impl loads
the current value of the waitable. This adds a __platform_load function,
which does an atomic load of the right size. For Linux, it's always
loading from int* but for FreeBSD it might be a 4B or 8B type.
Tested x86_64-linux and x86_64-freebsd.
I see a few unexplained FAILs when testing with -m32 on freebsd, but
they're already present on trunk so aren't caused by this patch. This
passes all tests with -m64 (and the changes should only affect 64-bit
more, because of the __SIZEOF_LONG__ == 8 check).
libstdc++-v3/include/bits/atomic_wait.h | 11 ++++
libstdc++-v3/src/c++20/atomic.cc | 78 ++++++++++++++++++++++++-
2 files changed, 87 insertions(+), 2 deletions(-)
diff --git a/libstdc++-v3/include/bits/atomic_wait.h
b/libstdc++-v3/include/bits/atomic_wait.h
index eff1be604eb4..e8487390ecb5 100644
--- a/libstdc++-v3/include/bits/atomic_wait.h
+++ b/libstdc++-v3/include/bits/atomic_wait.h
@@ -69,6 +69,17 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
inline constexpr bool __platform_wait_uses_type
= __detail::__waitable<_Tp>
&& sizeof(_Tp) == sizeof(int) && alignof(_Tp) >= 4;
+#elif defined __FreeBSD__ && __SIZEOF_LONG__ == 8
+ namespace __detail
+ {
+ using __platform_wait_t = __UINT64_TYPE__;
+ inline constexpr size_t __platform_wait_alignment = 8;
+ }
+ template<typename _Tp>
+ inline constexpr bool __platform_wait_uses_type
+ = __detail::__waitable<_Tp>
+ && ((sizeof(_Tp) == 4 && alignof(_Tp) >= 4)
+ || (sizeof(_Tp) == 8 && alignof(_Tp) >= 8));
#else
// define _GLIBCX_HAVE_PLATFORM_WAIT and implement __platform_wait()
// and __platform_notify() if there is a more efficient primitive supported
diff --git a/libstdc++-v3/src/c++20/atomic.cc b/libstdc++-v3/src/c++20/atomic.cc
index 3167592786e1..215f1212dd99 100644
--- a/libstdc++-v3/src/c++20/atomic.cc
+++ b/libstdc++-v3/src/c++20/atomic.cc
@@ -27,7 +27,7 @@
#if __glibcxx_atomic_wait
#include <atomic>
#include <bits/atomic_timed_wait.h>
-#include <cstdint> // uint32_t, uint64_t
+#include <cstdint> // uint32_t, uint64_t, uintptr_t
#include <climits> // INT_MAX
#include <cerrno> // errno, ETIMEDOUT, etc.
#include <bits/std_mutex.h> // std::mutex, std::__condvar
@@ -39,6 +39,11 @@
# include <unistd.h>
# include <sys/time.h> // timespec
# define _GLIBCXX_HAVE_PLATFORM_WAIT 1
+#elif defined __FreeBSD__ && __FreeBSD__ >= 11 && __SIZEOF_LONG__ == 8
+# include <sys/types.h>
+# include <sys/umtx.h>
+# include <sys/time.h>
+# define _GLIBCXX_HAVE_PLATFORM_WAIT 1
#endif
#pragma GCC diagnostic ignored "-Wmissing-field-initializers"
@@ -87,6 +92,13 @@ namespace
__wait_clock_t::time_point timeout,
int obj_size) = delete;
+ // This is needed even when we don't have __platform_wait
+ [[gnu::always_inline]]
+ inline __wait_value_type
+ __platform_load(const __platform_wait_t* addr, int memory_order,
+ int /* obj_sz */) noexcept
+ { return __atomic_load_n(addr, memory_order); }
+
#elif defined _GLIBCXX_HAVE_LINUX_FUTEX
const int futex_private_flag = 128;
@@ -136,6 +148,68 @@ namespace
}
return true;
}
+
+ [[gnu::always_inline]]
+ inline __wait_value_type
+ __platform_load(const int* addr, int order, int /* obj_sz */) noexcept
+ { return __atomic_load_n(addr, order); }
+
+#elif defined __FreeBSD__ && __SIZEOF_LONG__ == 8
+ [[gnu::always_inline]]
+ inline int
+ wait_op(int obj_sz) noexcept
+ { return obj_sz == sizeof(unsigned) ? UMTX_OP_WAIT_UINT : UMTX_OP_WAIT; }
+
+ void
+ __platform_wait(const void* addr, uint64_t val, int obj_sz) noexcept
+ {
+ if (_umtx_op(const_cast<void*>(addr), wait_op(obj_sz), val,
+ nullptr, nullptr))
+ if (errno != EINTR)
+ __throw_system_error(errno);
+ }
+
+ void
+ __platform_notify(const void* addr, bool all, int /* obj_sz */) noexcept
+ {
+ const int count = all ? INT_MAX : 1;
+ _umtx_op(const_cast<void*>(addr), UMTX_OP_WAKE, count, nullptr, nullptr);
+ }
+
+ // returns true if wait ended before timeout
+ bool
+ __platform_wait_until(const void* addr, uint64_t val,
+ const __wait_clock_t::time_point& atime,
+ int obj_sz) noexcept
+ {
+ struct _umtx_time timeout = {
+ ._timeout = chrono::__to_timeout_timespec(atime),
+ ._flags = UMTX_ABSTIME,
+ ._clockid = CLOCK_MONOTONIC
+ };
+ // _umtx_op hangs if timeout._timeout is {0, 0}
+ if (atime.time_since_epoch() < chrono::nanoseconds(1))
+ return false;
+ constexpr uintptr_t timeout_sz = sizeof(timeout);
+ if (_umtx_op(const_cast<void*>(addr), wait_op(obj_sz), val,
+ (void*)timeout_sz, &timeout))
+ {
+ if (errno == ETIMEDOUT)
+ return false;
+ if (errno != EINTR)
+ __throw_system_error(errno);
+ }
+ return true;
+ }
+
+ [[gnu::always_inline]]
+ inline __wait_value_type
+ __platform_load(const void* addr, int order, int obj_sz) noexcept
+ {
+ if (obj_sz == sizeof(long))
+ return __atomic_load_n(static_cast<const long*>(addr), order);
+ return __atomic_load_n(static_cast<const unsigned*>(addr), order);
+ }
#endif // HAVE_PLATFORM_WAIT
// The state used by atomic waiting and notifying functions.
@@ -259,7 +333,7 @@ namespace
__wait_value_type wval;
for (auto i = 0; i < atomic_spin_count; ++i)
{
- wval = __atomic_load_n(addr, args._M_order);
+ wval = __platform_load(addr, args._M_order, args._M_obj_size);
if (wval != args._M_old)
return { ._M_val = wval, ._M_has_val = true, ._M_timeout = false };
if (i < atomic_spin_count_relax)
--
2.52.0
