Re: [PATCH] Use unique_ptr for objfiles

[Bruno Larsen <blarsen@redhat.com>]

On 5/30/22 16:14, Tom Tromey wrote:
> A while back, I changed objfiles to be held via a shared_ptr.  The
> idea at the time was that this was a step toward writing to the index
> cache in the background, and this would let gdb keep a reference alive
> to do so.  However, since then we've rewritten the DWARF reader, and
> the new index can do this without requiring a shared pointer -- in
> fact there are patches pending to implement this.
> 
> This patch switches objfile management to unique_ptr, which makes more
> sense now.
> 

This patch seems obvious enough. It seems fine for me, I'd suggest you approve your patch.


> Regression tested on x86-64 Fedora 34.

Also tested on x86 fedora 35 and using clang. No regressions here either.

Cheers!
Bruno Larsen

> ---
>   gdb/objfiles.c  | 4 +---
>   gdb/objfiles.h  | 2 +-
>   gdb/progspace.c | 6 +++---
>   gdb/progspace.h | 8 ++++----
>   4 files changed, 9 insertions(+), 11 deletions(-)
> 
> diff --git a/gdb/objfiles.c b/gdb/objfiles.c
> index 80f68fda1c1..60d8aa5cb78 100644
> --- a/gdb/objfiles.c
> +++ b/gdb/objfiles.c
> @@ -468,9 +468,7 @@ objfile::make (bfd *bfd_, const char *name_, objfile_flags flags_,
>     if (parent != nullptr)
>       add_separate_debug_objfile (result, parent);
>   
> -  /* Using std::make_shared might be a bit nicer here, but that would
> -     require making the constructor public.  */
> -  current_program_space->add_objfile (std::shared_ptr<objfile> (result),
> +  current_program_space->add_objfile (std::unique_ptr<objfile> (result),
>   				      parent);
>   
>     /* Rebuild section map next time we need it.  */
> diff --git a/gdb/objfiles.h b/gdb/objfiles.h
> index 9da12ff12e0..a7098b46279 100644
> --- a/gdb/objfiles.h
> +++ b/gdb/objfiles.h
> @@ -409,7 +409,7 @@ struct objfile
>        remove it from the program space's list.  In some cases, you may
>        need to hold a reference to an objfile that is independent of its
>        existence on the program space's list; for this case, the
> -     destructor must be public so that shared_ptr can reference
> +     destructor must be public so that unique_ptr can reference
>        it.  */
>     ~objfile ();
>   
> diff --git a/gdb/progspace.c b/gdb/progspace.c
> index 1ee4fe3f940..8735343fabc 100644
> --- a/gdb/progspace.c
> +++ b/gdb/progspace.c
> @@ -174,7 +174,7 @@ program_space::free_all_objfiles ()
>   /* See progspace.h.  */
>   
>   void
> -program_space::add_objfile (std::shared_ptr<objfile> &&objfile,
> +program_space::add_objfile (std::unique_ptr<objfile> &&objfile,
>   			    struct objfile *before)
>   {
>     if (before == nullptr)
> @@ -182,7 +182,7 @@ program_space::add_objfile (std::shared_ptr<objfile> &&objfile,
>     else
>       {
>         auto iter = std::find_if (objfiles_list.begin (), objfiles_list.end (),
> -				[=] (const std::shared_ptr<::objfile> &objf)
> +				[=] (const std::unique_ptr<::objfile> &objf)
>   				{
>   				  return objf.get () == before;
>   				});
> @@ -203,7 +203,7 @@ program_space::remove_objfile (struct objfile *objfile)
>     reinit_frame_cache ();
>   
>     auto iter = std::find_if (objfiles_list.begin (), objfiles_list.end (),
> -			    [=] (const std::shared_ptr<::objfile> &objf)
> +			    [=] (const std::unique_ptr<::objfile> &objf)
>   			    {
>   			      return objf.get () == objfile;
>   			    });
> diff --git a/gdb/progspace.h b/gdb/progspace.h
> index 73beb7a4710..662e569488e 100644
> --- a/gdb/progspace.h
> +++ b/gdb/progspace.h
> @@ -41,9 +41,9 @@ struct program_space_data;
>   struct address_space_data;
>   struct so_list;
>   
> -typedef std::list<std::shared_ptr<objfile>> objfile_list;
> +typedef std::list<std::unique_ptr<objfile>> objfile_list;
>   
> -/* An iterator that wraps an iterator over std::shared_ptr<objfile>,
> +/* An iterator that wraps an iterator over std::unique_ptr<objfile>,
>      and dereferences the returned object.  This is useful for iterating
>      over a list of shared pointers and returning raw pointers -- which
>      helped avoid touching a lot of code when changing how objfiles are
> @@ -234,7 +234,7 @@ struct program_space
>     /* Add OBJFILE to the list of objfiles, putting it just before
>        BEFORE.  If BEFORE is nullptr, it will go at the end of the
>        list.  */
> -  void add_objfile (std::shared_ptr<objfile> &&objfile,
> +  void add_objfile (std::unique_ptr<objfile> &&objfile,
>   		    struct objfile *before);
>   
>     /* Remove OBJFILE from the list of objfiles.  */
> @@ -354,7 +354,7 @@ struct program_space
>     struct objfile *symfile_object_file = NULL;
>   
>     /* All known objfiles are kept in a linked list.  */
> -  std::list<std::shared_ptr<objfile>> objfiles_list;
> +  std::list<std::unique_ptr<objfile>> objfiles_list;
>   
>     /* List of shared objects mapped into this space.  Managed by
>        solib.c.  */