From b9b9d0a7db098e2b7e6894dca98ddd551067cad1 Mon Sep 17 00:00:00 2001
From: Jonathan Wakely <jwakely@redhat.com>
Date: Tue, 12 Sep 2023 12:04:37 +0100
Subject: libstdc++: Remove some more unconditional uses of atomics
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.
* include/experimental/memory_resource (__get_default_resource)
[!_GLIBCXX_HAS_GTHREADS]: Use unsynchronized type for
single-threaded targets.
* src/c++17/default_resource.h: Adjust preprocessor conditions
to match memory_resource.cc.
* 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/include/experimental/memory_resource | 12 +++++++-
libstdc++-v3/src/c++17/default_resource.h | 6 +++-
libstdc++-v3/src/c++17/memory_resource.cc | 35 ++++++++++++-----------
4 files changed, 38 insertions(+), 19 deletions(-)
(limited to 'libstdc++-v3')
diff --git a/libstdc++-v3/include/experimental/io_context b/libstdc++-v3/include/experimental/io_context
index c59f8c8..c878d5a 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/include/experimental/memory_resource b/libstdc++-v3/include/experimental/memory_resource
index 9f1cb42..6f419a0 100644
--- a/libstdc++-v3/include/experimental/memory_resource
+++ b/libstdc++-v3/include/experimental/memory_resource
@@ -549,10 +549,20 @@ namespace pmr {
// The default memory resource
/// @cond undocumented
- inline std::atomic<memory_resource*>&
+ inline auto&
__get_default_resource()
{
+#ifndef _GLIBCXX_HAS_GTHREADS
+ struct type {
+ using value_type = memory_resource*;
+ explicit type(value_type __r) : _M_r(__r) { }
+ value_type _M_r;
+ value_type load() const { return _M_r; }
+ value_type exchange(value_type __r) { return std::__exchange(_M_r, __r); }
+ };
+#else
using type = atomic<memory_resource*>;
+#endif
alignas(type) static unsigned char __buf[sizeof(type)];
static type* __r = new(__buf) type(new_delete_resource());
return *__r;
diff --git a/libstdc++-v3/src/c++17/default_resource.h b/libstdc++-v3/src/c++17/default_resource.h
index 522cee1..f8d03d7 100644
--- a/libstdc++-v3/src/c++17/default_resource.h
+++ b/libstdc++-v3/src/c++17/default_resource.h
@@ -2,7 +2,11 @@
// to suppress the warning caused by using a reserved init_priority.
#pragma GCC system_header
-#if ATOMIC_POINTER_LOCK_FREE == 2 || defined(__GTHREAD_MUTEX_INIT)
+#ifndef _GLIBCXX_HAS_GTHREADS
+# error "This file should not be included for this build"
+#elif ATOMIC_POINTER_LOCK_FREE == 2
+# error "This file should not be included for this build"
+#elif defined __GTHREAD_MUTEX_INIT
# error "This file should not be included for this build"
#endif
diff --git a/libstdc++-v3/src/c++17/memory_resource.cc b/libstdc++-v3/src/c++17/memory_resource.cc
index c0c7cf0..63856ea 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)
@@ -94,56 +94,57 @@ namespace pmr
__constinit constant_init<newdel_res_t> newdel_res{};
__constinit constant_init<null_res_t> null_res{};
-#if ATOMIC_POINTER_LOCK_FREE == 2
- using atomic_mem_res = atomic<memory_resource*>;
+
+#ifndef _GLIBCXX_HAS_GTHREADS
# define _GLIBCXX_ATOMIC_MEM_RES_CAN_BE_CONSTANT_INITIALIZED
-#elif defined(_GLIBCXX_HAS_GTHREADS)
- // Can't use pointer-width atomics, define a type using a mutex instead:
+ // Single-threaded, no need for synchronization
struct atomic_mem_res
{
-# ifdef __GTHREAD_MUTEX_INIT
-# define _GLIBCXX_ATOMIC_MEM_RES_CAN_BE_CONSTANT_INITIALIZED
- // std::mutex has constexpr constructor
constexpr
-# endif
atomic_mem_res(memory_resource* r) : val(r) { }
- mutex mx;
memory_resource* val;
- memory_resource* load(std::memory_order)
+ memory_resource* load(std::memory_order) const
{
- lock_guard<mutex> lock(mx);
return val;
}
memory_resource* exchange(memory_resource* r, std::memory_order)
{
- lock_guard<mutex> lock(mx);
return std::__exchange(val, r);
}
};
-#else
+#elif ATOMIC_POINTER_LOCK_FREE == 2
+ using atomic_mem_res = atomic<memory_resource*>;
# define _GLIBCXX_ATOMIC_MEM_RES_CAN_BE_CONSTANT_INITIALIZED
- // Single-threaded, no need for synchronization
+#else
+ // Can't use pointer-width atomics, define a type using a mutex instead:
struct atomic_mem_res
{
+# ifdef __GTHREAD_MUTEX_INIT
+# define _GLIBCXX_ATOMIC_MEM_RES_CAN_BE_CONSTANT_INITIALIZED
+ // std::mutex has constexpr constructor
constexpr
+# endif
atomic_mem_res(memory_resource* r) : val(r) { }
+ mutex mx;
memory_resource* val;
- memory_resource* load(std::memory_order) const
+ memory_resource* load(std::memory_order)
{
+ lock_guard<mutex> lock(mx);
return val;
}
memory_resource* exchange(memory_resource* r, std::memory_order)
{
+ lock_guard<mutex> lock(mx);
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};
--
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