switch TLS to C++11 TLS semantics

Rather than using the compiler specific `__thread` mechanism for TLS, use the
C++11 standard `thread_local` keyword.  This removes the check for the
`__thread` keyword and the `PALUDIS_TLS` macro in the single usage site.

Take advantage of the fact that `thread_local` can be applied to non-POD types
to avoid the heap allocation of the context buffer and letting the loader
perform the allocation.  This has a slight penalty (an extra function call) on
thread construction.  However, given that the heap allocation would likely be
performed, this will be largely offset by the loss of the allocation.

3 files changed, 7 insertions, 28 deletions

diff --git a/configure.ac b/configure.ac
index da6ee9b..7c1fe4f 100644
--- a/configure.ac
+++ b/configure.ac
@@ -235,17 +235,6 @@ fi
 
 PTHREAD_LIBS=""
 RT_LIBS=""
-AC_MSG_CHECKING([for compiler __thread support])
-AC_COMPILE_IFELSE([AC_LANG_SOURCE([
-int main(int, char **)
-{
-	static __thread int x(0);
-	return x;
-}
-])],
-[AC_MSG_RESULT([yes])],
-[AC_MSG_RESULT([no])
-AC_MSG_ERROR([Your compiler does not support __thread])])
 
 AC_MSG_CHECKING([whether -pthread -lpthread gets us posix threads])
 save_CXXFLAGS=$CXXFLAGS
diff --git a/paludis/util/attributes.hh b/paludis/util/attributes.hh
index 270fbc3..88877f6 100644
--- a/paludis/util/attributes.hh
+++ b/paludis/util/attributes.hh
@@ -63,6 +63,4 @@
 #  define PALUDIS_HIDDEN PALUDIS_ATTRIBUTE((visibility("hidden")))
 #endif
 
-#define PALUDIS_TLS static __thread
-
 #endif
diff --git a/paludis/util/exception.cc b/paludis/util/exception.cc
index 391f1e4..d0ce9d2 100644
--- a/paludis/util/exception.cc
+++ b/paludis/util/exception.cc
@@ -35,35 +35,28 @@ using namespace paludis;
 
 namespace
 {
-    PALUDIS_TLS std::list<std::string> * context = 0;
+    static thread_local std::list<std::string> context;
 }
 
 Context::Context(const std::string & s)
 {
-    if (! context)
-        context = new std::list<std::string>;
-    context->push_back(s);
+    context.push_back(s);
 }
 
 Context::~Context() noexcept(false)
 {
-    if (! context)
+    if (context.empty())
         throw InternalError(PALUDIS_HERE, "no context");
-    context->pop_back();
-    if (context->empty())
-    {
-        delete context;
-        context = 0;
-    }
+    context.pop_back();
 }
 
 std::string
 Context::backtrace(const std::string & delim)
 {
-    if (! context)
+    if (context.empty())
         return "";
 
-    return join(context->begin(), context->end(), delim) + delim;
+    return join(context.begin(), context.end(), delim) + delim;
 }
 
 namespace paludis
@@ -74,8 +67,7 @@ namespace paludis
 
         ContextData()
         {
-            if (context)
-                local_context.assign(context->begin(), context->end());
+            local_context.assign(context.begin(), context.end());
         }
 
         ContextData(const ContextData & other) :