Fix protobuf static memory leak

protobuf - fix memory leak of statically initialized generated descriptor objects (C++)

The reflection_ and default_instance_ objects allocated in the
BuildDescriptors functions at static initialization time are not destructed
prior to process teardown.  This causes memory leak checkers (such as the
one in MSVC) to complain.

This change fixes the issue by making protoc also generate a destructor that
deletes these objects.

(Only the message objects actually have anything to destruct, but I've added
placeholders for enums and services to help encourage cleanup of these if
required in the future.)

See http://code.google.com/p/protobuf/issues/detail?id=54

Tested with MSVC 8.0.  All tests pass.

[kenton, 2008-11-04 02:52:13]

Mostly looks good.  I think you should just remove the empty methods.

I guess there is no good way to add a test case for this?

You will also need to sign the Contributor License Agreement before we can
accept this patch.

http://code.google.com/legal/individual-cla-v1.0.html -- if you own the
copyright on this work.
http://code.google.com/legal/corporate-cla-v1.0.html -- if your employer owns
it.

Thanks!

http://codereview.appspot.com/7918/diff/1/5
File google/protobuf/compiler/cpp/cpp_enum.cc (right):

http://codereview.appspot.com/7918/diff/1/5#newcode149
Line 149: // Nothing to do here
Then why define this method at all?

http://codereview.appspot.com/7918/diff/1/7
File google/protobuf/compiler/cpp/cpp_file.cc (right):

http://codereview.appspot.com/7918/diff/1/7#newcode330
Line 330: map<string, string> vars;
This doesn't appear to be used.

http://codereview.appspot.com/7918/diff/1/8
File google/protobuf/compiler/cpp/cpp_message.cc (right):

http://codereview.appspot.com/7918/diff/1/8#newcode510
Line 510: "friend void protobuf_DestroyDesc_$filename$();\n");
I'd name this $builddescriptorsname$_TearDown() instead for consistency.  (And
then you don't have to add a new variable to vars.)

http://codereview.appspot.com/7918/diff/1/9
File google/protobuf/compiler/cpp/cpp_message.h (right):

http://codereview.appspot.com/7918/diff/1/9#newcode94
Line 94: void GenerateDescriptorDestructor(io::Printer* printer);
The code that this method generates doesn't actually destroy the descriptor.  It
destroys the default instance and reflection objects.  Perhaps
"GenerateTearDown()" would be a better name?

http://codereview.appspot.com/7918/diff/1/3
File google/protobuf/compiler/cpp/cpp_service.cc (right):

http://codereview.appspot.com/7918/diff/1/3#newcode174
Line 174: // Nothing to do here
Then why define this method at all?