Re: [PATCH] Use unique_ptr for objfiles

[Andrew Burgess <aburgess@redhat.com>]

* Tom Tromey <tom@tromey.com> [2022-05-30 13:14:21 -0600]:

> 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.

LGTM.

Thanks,
Andrew

> 
> Regression tested on x86-64 Fedora 34.
> ---
>  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.  */
> -- 
> 2.34.1
>