Clenaup Q_COMPILER_THREADSAFE_STATICS

Change-Id: I1cf0646d4e6c9b30a7ef6538d81f92faf2e511e1
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

2 files changed, 5 insertions, 55 deletions

diff --git a/src/corelib/global/qcompilerdetection.h b/src/corelib/global/qcompilerdetection.h
index d1ce56fd0a..cc48355ff0 100644
--- a/src/corelib/global/qcompilerdetection.h
+++ b/src/corelib/global/qcompilerdetection.h
@@ -378,7 +378,6 @@
 #        define Q_COMPILER_STATIC_ASSERT
 #        define Q_COMPILER_TEMPLATE_ALIAS
 #        define Q_COMPILER_THREAD_LOCAL
-#        define Q_COMPILER_THREADSAFE_STATICS
 #        define Q_COMPILER_UDL
 #        define Q_COMPILER_UNICODE_STRINGS
 #        define Q_COMPILER_UNIFORM_INIT
@@ -573,6 +572,11 @@
  *  Q_COMPILER_RESTRICTED_VLA       variable-length arrays, prior to __cpp_runtime_arrays
  */
 
+/*
+ * Now that we require C++17, we unconditionally expect threadsafe statics mandated since C++11
+ */
+#define Q_COMPILER_THREADSAFE_STATICS
+
 #ifdef __cplusplus
 #  if __cplusplus < 201103L && !defined(Q_CC_MSVC)
 #    error Qt requires a C++11 compiler and yours does not seem to be that.
@@ -582,7 +586,6 @@
 #if defined(Q_CC_INTEL) && !defined(Q_CC_MSVC)
 #  define Q_COMPILER_RESTRICTED_VLA
 #  define Q_COMPILER_VARIADIC_MACROS // C++11 feature supported as an extension in other modes, too
-#  define Q_COMPILER_THREADSAFE_STATICS
 #  if __INTEL_COMPILER < 1200
 #    define Q_NO_TEMPLATE_FRIENDS
 #  endif
@@ -658,7 +661,6 @@
 #if defined(Q_CC_CLANG) && !defined(Q_CC_INTEL) && !defined(Q_CC_MSVC)
 /* General C++ features */
 #  define Q_COMPILER_RESTRICTED_VLA
-#  define Q_COMPILER_THREADSAFE_STATICS
 #  if __has_feature(attribute_deprecated_with_message)
 #    define Q_DECL_DEPRECATED_X(text) __attribute__ ((__deprecated__(text)))
 #  endif
@@ -826,7 +828,6 @@
 
 #if defined(Q_CC_GNU) && !defined(Q_CC_INTEL) && !defined(Q_CC_CLANG)
 #  define Q_COMPILER_RESTRICTED_VLA
-#  define Q_COMPILER_THREADSAFE_STATICS
 #  if Q_CC_GNU >= 403
 //   GCC supports binary literals in C, C++98 and C++11 modes
 #    define Q_COMPILER_BINARY_LITERALS
@@ -980,7 +981,6 @@
 #      define Q_COMPILER_ATTRIBUTES
 // Almost working, see https://connect.microsoft.com/VisualStudio/feedback/details/2011648
 //#      define Q_COMPILER_CONSTEXPR
-#      define Q_COMPILER_THREADSAFE_STATICS
 #      define Q_COMPILER_UNIFORM_INIT
 #    endif
 #    if _MSC_VER >= 1910
@@ -1048,13 +1048,6 @@
 #  define __USE_CONSTEXPR 1
 #  define __USE_NOEXCEPT 1
 # endif
-# if defined(Q_COMPILER_THREADSAFE_STATICS) && defined(Q_OS_MAC)
-// Apple's low-level implementation of the C++ support library
-// (libc++abi.dylib, shared between libstdc++ and libc++) has deadlocks. The
-// C++11 standard requires the deadlocks to be removed, so this will eventually
-// be fixed; for now, let's disable this.
-#  undef Q_COMPILER_THREADSAFE_STATICS
-# endif
 #endif
 
 /*
diff --git a/src/corelib/global/qglobalstatic.h b/src/corelib/global/qglobalstatic.h
index 674a2aea65..034ef274fa 100644
--- a/src/corelib/global/qglobalstatic.h
+++ b/src/corelib/global/qglobalstatic.h
@@ -55,17 +55,6 @@ enum GuardValues {
 };
 }
 
-#if !QT_CONFIG(thread) || defined(Q_COMPILER_THREADSAFE_STATICS)
-// some compilers support thread-safe statics
-// The IA-64 C++ ABI requires this, so we know that all GCC versions since 3.4
-// support it. C++11 also requires this behavior.
-// Clang and Intel CC masquerade as GCC when compiling on Linux.
-//
-// Apple's libc++abi however uses a global lock for initializing local statics,
-// which will block other threads also trying to initialize a local static
-// until the constructor returns ...
-// We better avoid these kind of problems by using our own locked implementation.
-
 #if defined(Q_OS_UNIX) && defined(Q_CC_INTEL)
 // Work around Intel issue ID 6000058488:
 // local statics inside an inline function inside an anonymous namespace are global
@@ -94,39 +83,7 @@ enum GuardValues {
         } holder;                                               \
         return &holder.value;                                   \
     }
-#else
-// We don't know if this compiler supports thread-safe global statics
-// so use our own locked implementation
 
-QT_END_NAMESPACE
-#include <QtCore/qmutex.h>
-#include <mutex>
-QT_BEGIN_NAMESPACE
-
-#define Q_GLOBAL_STATIC_INTERNAL(ARGS)                                  \
-    Q_DECL_HIDDEN inline Type *innerFunction()                          \
-    {                                                                   \
-        static Type *d;                                                 \
-        static QBasicMutex mutex;                                       \
-        int x = guard.loadAcquire();                                    \
-        if (Q_UNLIKELY(x >= QtGlobalStatic::Uninitialized)) {           \
-            const std::lock_guard<QBasicMutex> locker(mutex);           \
-            if (guard.loadRelaxed() == QtGlobalStatic::Uninitialized) {        \
-                d = new Type ARGS;                                      \
-                static struct Cleanup {                                 \
-                    Cleanup() = default;                                \
-                    ~Cleanup() {                                        \
-                        delete d;                                       \
-                        guard.storeRelaxed(QtGlobalStatic::Destroyed);         \
-                    }                                                   \
-                    Q_DISABLE_COPY_MOVE(Cleanup)                        \
-                } cleanup;                                              \
-                guard.storeRelease(QtGlobalStatic::Initialized);        \
-            }                                                           \
-        }                                                               \
-        return d;                                                       \
-    }
-#endif
 
 // this class must be POD, unless the compiler supports thread-safe statics
 template <typename T, T *(&innerFunction)(), QBasicAtomicInt &guard>