From: Jonathan Wakely <jwakely@redhat.com>
To: libstdc++@gcc.gnu.org, gcc-patches@gcc.gnu.org
Cc: Christophe Lyon <christophe.lyon@linaro.org>
Subject: [PATCH] libstdc++: Remove some more unconditional uses of atomics
Date: Wed, 13 Sep 2023 13:31:40 +0100 [thread overview]
Message-ID: <20230913123226.2083892-1-jwakely@redhat.com> (raw)
Tested x86_64-linux and aarch64-linux. I intend to push this to trunk.
-- >8 --
These atomics cause linker errors on arm4t where __sync_synchronize is
not defined. For single-threaded targets we don't need the atomics.
libstdc++-v3/ChangeLog:
* include/experimental/io_context (io_context) [!_GLIBCXX_HAS_GTHREADS]:
Use a plain integer for _M_work_count for single-threaded
targets.
* src/c++17/memory_resource.cc [!_GLIBCXX_HAS_GTHREADS]
(atomic_mem_res): Use unsynchronized type for single-threaded
targets.
---
libstdc++-v3/include/experimental/io_context | 4 ++
libstdc++-v3/src/c++17/memory_resource.cc | 49 ++++++++++----------
2 files changed, 29 insertions(+), 24 deletions(-)
diff --git a/libstdc++-v3/include/experimental/io_context b/libstdc++-v3/include/experimental/io_context
index c59f8c8e73b..c878d5a7025 100644
--- a/libstdc++-v3/include/experimental/io_context
+++ b/libstdc++-v3/include/experimental/io_context
@@ -562,7 +562,11 @@ inline namespace v1
}
};
+#ifdef _GLIBCXX_HAS_GTHREADS
atomic<count_type> _M_work_count;
+#else
+ count_type _M_work_count;
+#endif
mutable execution_context::mutex_type _M_mtx;
queue<function<void()>> _M_op;
bool _M_stopped = false;
diff --git a/libstdc++-v3/src/c++17/memory_resource.cc b/libstdc++-v3/src/c++17/memory_resource.cc
index c0c7cf0cf83..63856eadaf5 100644
--- a/libstdc++-v3/src/c++17/memory_resource.cc
+++ b/libstdc++-v3/src/c++17/memory_resource.cc
@@ -27,9 +27,9 @@
#include <atomic>
#include <bit> // has_single_bit, bit_ceil, bit_width
#include <new>
+#include <bits/move.h> // std::__exchange
#if ATOMIC_POINTER_LOCK_FREE != 2
# include <bits/std_mutex.h> // std::mutex, std::lock_guard
-# include <bits/move.h> // std::__exchange
#endif
#if __has_cpp_attribute(clang::require_constant_initialization)
@@ -94,10 +94,31 @@ namespace pmr
__constinit constant_init<newdel_res_t> newdel_res{};
__constinit constant_init<null_res_t> null_res{};
-#if ATOMIC_POINTER_LOCK_FREE == 2
+
+#ifndef _GLIBCXX_HAS_GTHREADS
+# define _GLIBCXX_ATOMIC_MEM_RES_CAN_BE_CONSTANT_INITIALIZED
+ // Single-threaded, no need for synchronization
+ struct atomic_mem_res
+ {
+ constexpr
+ atomic_mem_res(memory_resource* r) : val(r) { }
+
+ memory_resource* val;
+
+ memory_resource* load(std::memory_order) const
+ {
+ return val;
+ }
+
+ memory_resource* exchange(memory_resource* r, std::memory_order)
+ {
+ return std::__exchange(val, r);
+ }
+ };
+#elif ATOMIC_POINTER_LOCK_FREE == 2
using atomic_mem_res = atomic<memory_resource*>;
# define _GLIBCXX_ATOMIC_MEM_RES_CAN_BE_CONSTANT_INITIALIZED
-#elif defined(_GLIBCXX_HAS_GTHREADS)
+#else
// Can't use pointer-width atomics, define a type using a mutex instead:
struct atomic_mem_res
{
@@ -123,27 +144,7 @@ namespace pmr
return std::__exchange(val, r);
}
};
-#else
-# define _GLIBCXX_ATOMIC_MEM_RES_CAN_BE_CONSTANT_INITIALIZED
- // Single-threaded, no need for synchronization
- struct atomic_mem_res
- {
- constexpr
- atomic_mem_res(memory_resource* r) : val(r) { }
-
- memory_resource* val;
-
- memory_resource* load(std::memory_order) const
- {
- return val;
- }
-
- memory_resource* exchange(memory_resource* r, std::memory_order)
- {
- return std::__exchange(val, r);
- }
- };
-#endif // ATOMIC_POINTER_LOCK_FREE == 2
+#endif
#ifdef _GLIBCXX_ATOMIC_MEM_RES_CAN_BE_CONSTANT_INITIALIZED
__constinit constant_init<atomic_mem_res> default_res{&newdel_res.obj};
--
2.41.0
next reply other threads:[~2023-09-13 12:32 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-09-13 12:31 Jonathan Wakely [this message]
2023-09-14 7:43 ` Christophe Lyon
2023-09-14 8:17 ` Jonathan Wakely
2023-09-14 8:41 ` Christophe Lyon
2023-09-14 9:06 ` Jonathan Wakely
2023-09-14 9:11 ` Christophe Lyon
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