Revert of Refactor thread_local.h's TLS Implementation to use ThreadLocalStorage

base/threading/thread_local.h

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// WARNING: Thread local storage is a bit tricky to get right. Please make sure
-// that this is really the proper solution for what you're trying to achieve.
-// Don't prematurely optimize, most likely you can just use a Lock.
+// WARNING: Thread local storage is a bit tricky to get right.  Please make
+// sure that this is really the proper solution for what you're trying to
+// achieve.  Don't prematurely optimize, most likely you can just use a Lock.
 //
-// These classes implement a wrapper around ThreadLocalStorage::Slot. On
-// construction, they will allocate a TLS slot, and free the TLS slot on
-// destruction. No memory management (creation or destruction) is handled. This
-// means for uses of ThreadLocalPointer, you must correctly manage the memory
-// yourself, these classes will not destroy the pointer for you. There are no
-// at-thread-exit actions taken by these classes.
+// These classes implement a wrapper around the platform's TLS storage
+// mechanism.  On construction, they will allocate a TLS slot, and free the
+// TLS slot on destruction.  No memory management (creation or destruction) is
+// handled.  This means for uses of ThreadLocalPointer, you must correctly
+// manage the memory yourself, these classes will not destroy the pointer for
+// you.  There are no at-thread-exit actions taken by these classes.
 //
-// ThreadLocalPointer<Type> wraps a Type*. It performs no creation or
-// destruction, so memory management must be handled elsewhere. The first call
-// to Get() on a thread will return NULL. You can update the pointer with a call
-// to Set().
+// ThreadLocalPointer<Type> wraps a Type*.  It performs no creation or
+// destruction, so memory management must be handled elsewhere.  The first call
+// to Get() on a thread will return NULL.  You can update the pointer with a
+// call to Set().
 //
-// ThreadLocalBoolean wraps a bool. It will default to false if it has never
+// ThreadLocalBoolean wraps a bool.  It will default to false if it has never
 // been set otherwise with Set().
 //
-// Thread Safety: An instance of ThreadLocalStorage is completely thread safe
-// once it has been created. If you want to dynamically create an instance, you
-// must of course properly deal with safety and race conditions. This means a
-// function-level static initializer is generally inappropiate.
+// Thread Safety:  An instance of ThreadLocalStorage is completely thread safe
+// once it has been created.  If you want to dynamically create an instance,
+// you must of course properly deal with safety and race conditions.  This
+// means a function-level static initializer is generally inappropiate.
 //
-// In Android, the system TLS is limited.
+// In Android, the system TLS is limited, the implementation is backed with
+// ThreadLocalStorage.
 //
 // Example usage:
-//   // My class is logically attached to a single thread. We cache a pointer
+//   // My class is logically attached to a single thread.  We cache a pointer
 //   // on the thread it was created on, so we can implement current().
 //   MyClass::MyClass() {
 //     DCHECK(Singleton<ThreadLocalPointer<MyClass> >::get()->Get() == NULL);
 //     Singleton<ThreadLocalPointer<MyClass> >::get()->Set(this);
 //   }
 //
 //   MyClass::~MyClass() {
 //     DCHECK(Singleton<ThreadLocalPointer<MyClass> >::get()->Get() != NULL);
 //     Singleton<ThreadLocalPointer<MyClass> >::get()->Set(NULL);
 //   }
 //
 //   // Return the current MyClass associated with the calling thread, can be
 //   // NULL if there isn't a MyClass associated.
 //   MyClass* MyClass::current() {
 //     return Singleton<ThreadLocalPointer<MyClass> >::get()->Get();
 //   }
 
 #ifndef BASE_THREADING_THREAD_LOCAL_H_
 #define BASE_THREADING_THREAD_LOCAL_H_
 
+#include "base/base_export.h"
 #include "base/macros.h"
 #include "base/threading/thread_local_storage.h"
+#include "build/build_config.h"
+
+#if defined(OS_POSIX)
+#include <pthread.h>
+#endif
 
 namespace base {
+namespace internal {
+
+// Helper functions that abstract the cross-platform APIs.  Do not use directly.
+struct BASE_EXPORT ThreadLocalPlatform {
+#if defined(OS_WIN)
+  typedef unsigned long SlotType;
+#elif defined(OS_ANDROID)
+  typedef ThreadLocalStorage::StaticSlot SlotType;
+#elif defined(OS_POSIX)
+  typedef pthread_key_t SlotType;
+#endif
+
+  static void AllocateSlot(SlotType* slot);
+  static void FreeSlot(SlotType slot);
+  static void* GetValueFromSlot(SlotType slot);
+  static void SetValueInSlot(SlotType slot, void* value);
+};
+
+}  // namespace internal
 
 template <typename Type>
 class ThreadLocalPointer {
  public:
-  ThreadLocalPointer() = default;
-  ~ThreadLocalPointer() = default;
+  ThreadLocalPointer() : slot_() {
+    internal::ThreadLocalPlatform::AllocateSlot(&slot_);
+  }
+
+  ~ThreadLocalPointer() {
+    internal::ThreadLocalPlatform::FreeSlot(slot_);
+  }
 
   Type* Get() {
-    return static_cast<Type*>(slot_.Get());
+    return static_cast<Type*>(
+        internal::ThreadLocalPlatform::GetValueFromSlot(slot_));
   }
 
   void Set(Type* ptr) {
-    slot_.Set(const_cast<void*>(static_cast<const void*>(ptr)));
+    internal::ThreadLocalPlatform::SetValueInSlot(
+        slot_, const_cast<void*>(static_cast<const void*>(ptr)));
   }
 
  private:
-  ThreadLocalStorage::Slot slot_;
+  typedef internal::ThreadLocalPlatform::SlotType SlotType;
+
+  SlotType slot_;
 
   DISALLOW_COPY_AND_ASSIGN(ThreadLocalPointer<Type>);
 };
 
 class ThreadLocalBoolean {
  public:
-  ThreadLocalBoolean() = default;
-  ~ThreadLocalBoolean() = default;
+  ThreadLocalBoolean() {}
+  ~ThreadLocalBoolean() {}
 
   bool Get() {
-    return tlp_.Get() != nullptr;
+    return tlp_.Get() != NULL;
   }
 
   void Set(bool val) {
-    tlp_.Set(val ? this : nullptr);
+    tlp_.Set(val ? this : NULL);
   }
 
  private:
   ThreadLocalPointer<void> tlp_;
 
   DISALLOW_COPY_AND_ASSIGN(ThreadLocalBoolean);
 };
 
 }  // namespace base
 
 #endif  // BASE_THREADING_THREAD_LOCAL_H_