Do not create an extra default instance of T when constructing a ThreadLocal<T>.

include/gtest/internal/gtest-port.h

@@ -1838,8 +1838,9 @@ class ThreadWithParam : public ThreadWithParamBase {
 template <typename T>
 class ThreadLocal : public ThreadLocalBase {
  public:
-  ThreadLocal() : default_() {}
-  explicit ThreadLocal(const T& value) : default_(value) {}
+  ThreadLocal() : default_factory_(new DefaultValueHolderFactory()) {}
+  explicit ThreadLocal(const T& value)
+      : default_factory_(new InstanceValueHolderFactory(value)) {}
 
   ~ThreadLocal() { ThreadLocalRegistry::OnThreadLocalDestroyed(this); }
 
@@ -1853,6 +1854,7 @@ class ThreadLocal : public ThreadLocalBase {
   // knowing the type of T.
   class ValueHolder : public ThreadLocalValueHolderBase {
    public:
+    ValueHolder() : value_() {}
     explicit ValueHolder(const T& value) : value_(value) {}
 
     T* pointer() { return &value_; }
@@ -1869,10 +1871,42 @@ class ThreadLocal : public ThreadLocalBase {
   }
 
   virtual ThreadLocalValueHolderBase* NewValueForCurrentThread() const {
-    return new ValueHolder(default_);
+    return default_factory_->MakeNewHolder();
   }
 
-  const T default_;  // The default value for each thread.
+  class ValueHolderFactory {
+   public:
+    ValueHolderFactory() {}
+    virtual ~ValueHolderFactory() {}
+    virtual ValueHolder* MakeNewHolder() const = 0;
+
+   private:
+    GTEST_DISALLOW_COPY_AND_ASSIGN_(ValueHolderFactory);
+  };
+
+  class DefaultValueHolderFactory : public ValueHolderFactory {
+   public:
+    DefaultValueHolderFactory() {}
+    virtual ValueHolder* MakeNewHolder() const { return new ValueHolder(); }
+
+   private:
+    GTEST_DISALLOW_COPY_AND_ASSIGN_(DefaultValueHolderFactory);
+  };
+
+  class InstanceValueHolderFactory : public ValueHolderFactory {
+   public:
+    explicit InstanceValueHolderFactory(const T& value) : value_(value) {}
+    virtual ValueHolder* MakeNewHolder() const {
+      return new ValueHolder(value_);
+    }
+
+   private:
+    const T value_;  // The value for each thread.
+
+    GTEST_DISALLOW_COPY_AND_ASSIGN_(InstanceValueHolderFactory);
+  };
+
+  scoped_ptr<ValueHolderFactory> default_factory_;
 
   GTEST_DISALLOW_COPY_AND_ASSIGN_(ThreadLocal);
 };
@@ -1993,10 +2027,11 @@ extern "C" inline void DeleteThreadLocalValue(void* value_holder) {
 template <typename T>
 class ThreadLocal {
  public:
-  ThreadLocal() : key_(CreateKey()),
-                  default_() {}
-  explicit ThreadLocal(const T& value) : key_(CreateKey()),
-                                         default_(value) {}
+  ThreadLocal()
+      : key_(CreateKey()), default_factory_(new DefaultValueHolderFactory()) {}
+  explicit ThreadLocal(const T& value)
+      : key_(CreateKey()),
+        default_factory_(new InstanceValueHolderFactory(value)) {}
 
   ~ThreadLocal() {
     // Destroys the managed object for the current thread, if any.
@@ -2016,6 +2051,7 @@ class ThreadLocal {
   // Holds a value of type T.
   class ValueHolder : public ThreadLocalValueHolderBase {
    public:
+    ValueHolder() : value_() {}
     explicit ValueHolder(const T& value) : value_(value) {}
 
     T* pointer() { return &value_; }
@@ -2041,15 +2077,47 @@ class ThreadLocal {
       return CheckedDowncastToActualType<ValueHolder>(holder)->pointer();
     }
 
-    ValueHolder* const new_holder = new ValueHolder(default_);
+    ValueHolder* const new_holder = default_factory_->MakeNewHolder();
     ThreadLocalValueHolderBase* const holder_base = new_holder;
     GTEST_CHECK_POSIX_SUCCESS_(pthread_setspecific(key_, holder_base));
     return new_holder->pointer();
   }
 
+  class ValueHolderFactory {
+   public:
+    ValueHolderFactory() {}
+    virtual ~ValueHolderFactory() {}
+    virtual ValueHolder* MakeNewHolder() const = 0;
+
+   private:
+    GTEST_DISALLOW_COPY_AND_ASSIGN_(ValueHolderFactory);
+  };
+
+  class DefaultValueHolderFactory : public ValueHolderFactory {
+   public:
+    DefaultValueHolderFactory() {}
+    virtual ValueHolder* MakeNewHolder() const { return new ValueHolder(); }
+
+   private:
+    GTEST_DISALLOW_COPY_AND_ASSIGN_(DefaultValueHolderFactory);
+  };
+
+  class InstanceValueHolderFactory : public ValueHolderFactory {
+   public:
+    explicit InstanceValueHolderFactory(const T& value) : value_(value) {}
+    virtual ValueHolder* MakeNewHolder() const {
+      return new ValueHolder(value_);
+    }
+
+   private:
+    const T value_;  // The value for each thread.
+
+    GTEST_DISALLOW_COPY_AND_ASSIGN_(InstanceValueHolderFactory);
+  };
+
   // A key pthreads uses for looking up per-thread values.
   const pthread_key_t key_;
-  const T default_;  // The default value for each thread.
+  scoped_ptr<ValueHolderFactory> default_factory_;
 
   GTEST_DISALLOW_COPY_AND_ASSIGN_(ThreadLocal);
 };