Subzero: Second attempt at fixing MacOS 10.6 build.

src/IceTLS.h

+//===- subzero/src/IceTLS.h - thread_local workaround -----------*- C++ -*-===//
+//
+//                        The Subzero Code Generator
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file defines macros for working around the lack of support for
+// thread_local in MacOS 10.6.  It assumes std::thread is written in
+// terms of pthread.  Define ICE_THREAD_LOCAL_HACK to enable the
+// pthread workarounds.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef SUBZERO_SRC_ICETLS_H
+#define SUBZERO_SRC_ICETLS_H
+
+// Defines 4 macros for unifying thread_local and pthread:
+//
+// ICE_TLS_DECLARE_FIELD(FieldName, Type): Declare a static
+// thread_local field inside the current class definition.  "Type"
+// needs to be a pointer type, such as int* or class Foo*.
+//
+// ICE_TLS_DEFINE_FIELD(ClassName, FieldName, Type): Define a static
+// thread_local field outside of its class definition, and initialize
+// it to nullptr.
+//
+// ICE_TLS_GET_FIELD(FieldName, Type): Read the value of the static
+// thread_local field.  Must be done within the context of its class.
+//
+// ICE_TLS_SET_FIELD(FieldName, Value): Write a value into the static
+// thread_local field.  Must be done within the context of its class.

[JF, 2015/01/24 05:42:47]

I have a mild preference for argument order being the same as in code: Type,
Class, Name, Value.

[Jim Stichnoth, 2015/01/24 16:55:33]

Done.

+
+#ifdef ICE_THREAD_LOCAL_HACK
+
+// For a static thread_local field F of a class C, instead of
+// declaring and defining F::C, we create two static fields:
+//   static pthread_key_t F__key;
+//   static int F__dummy;
+//
+// The F__dummy field is just used to hold the result of the
+// pthread_key_create() call, which is executed as a static
+// initializer.  The F__key field is used as the argument to
+// pthread_getspecific() and pthread_setspecific().
+
+#include <pthread.h>
+
+#define ICE_TLS_DECLARE_FIELD(FieldName, Type)                                 \
+  static pthread_key_t FieldName##__key;                                       \
+  static int FieldName##__dummy
+#define ICE_TLS_DEFINE_FIELD(ClassName, FieldName, Type)                       \
+  pthread_key_t ClassName::FieldName##__key;                                   \
+  int ClassName::FieldName##__dummy =                                          \
+      pthread_key_create(&ClassName::FieldName##__key, nullptr)

[JF, 2015/01/24 05:42:47]

It's not clear from the pthread docs that you can't legally call
pthread_key_create as a global static initializer. This paragraph especially
makes me think it may not be guaranteed to work:

Thus, this proposal was rejected. The pthread_key_create() function performs no
implicit synchronization. It is the responsibility of the programmer to ensure
that it is called exactly once per key before use of the key. Several
straightforward mechanisms can already be used to accomplish this, including
calling explicit module initialization functions, using mutexes, and using
pthread_once(). This places no significant burden on the programmer, introduces
no possibly confusing ad hoc implicit synchronization mechanism, and potentially
allows commonly used thread-specific data operations to be more efficient.


Maybe a global init function would be better (if a bit more annoying)?

[Jim Stichnoth, 2015/01/24 16:55:33]

I don't see how that could be a problem here, unless the C++ runtime is allowed
to run dynamic initializers in parallel?  Even if the dynamic initializers
somehow get run more than once, it wouldn't be a problem because the keys are
never used before dynamic initialization completes.

+#define ICE_TLS_GET_FIELD(FieldName, Type)                                     \
+  static_cast<Type>(pthread_getspecific(FieldName##__key))
+#define ICE_TLS_SET_FIELD(FieldName, Value)                                    \
+  pthread_setspecific(FieldName##__key, (Value))
+
+#else // !ICE_THREAD_LOCAL_HACK
+
+#define ICE_TLS_DECLARE_FIELD(FieldName, Type)                                 \
+  static thread_local Type FieldName
+#define ICE_TLS_DEFINE_FIELD(ClassName, FieldName, Type)                       \
+  thread_local Type ClassName::FieldName = nullptr
+#define ICE_TLS_GET_FIELD(FieldName, Type) (FieldName)
+#define ICE_TLS_SET_FIELD(FieldName, Value) (FieldName = (Value))
+
+#endif // !ICE_THREAD_LOCAL_HACK
+
+#endif // SUBZERO_SRC_ICETLS_H