Re: [PATCH] gdb: make all_inferiors_safe actually work

[Tom de Vries <tdevries@suse.de>]

On 7/14/21 10:15 PM, Simon Marchi wrote:
> The test gdb.threads/fork-plus-threads.exp fails since 08bdefb58b78
> ("gdb: make inferior_list use intrusive_list"):
> 
>     FAIL: gdb.threads/fork-plus-threads.exp: detach-on-fork=off: only inferior 1 left
> 
> Looking at the log, we see that we are left with a bunch of inferiors in
> the detach-on-fork=off case:
> 
>     info inferiors^M
>       Num  Description       Connection           Executable        ^M
>     * 1    <null>                                 /home/simark/build/binutils-gdb/gdb/testsuite/outputs/gdb.threads/fork-plus-threads/fork-plus-threads ^M
>       2    <null>                                 /home/simark/build/binutils-gdb/gdb/testsuite/outputs/gdb.threads/fork-plus-threads/fork-plus-threads ^M
>       3    <null>                                 /home/simark/build/binutils-gdb/gdb/testsuite/outputs/gdb.threads/fork-plus-threads/fork-plus-threads ^M
>       4    <null>                                 /home/simark/build/binutils-gdb/gdb/testsuite/outputs/gdb.threads/fork-plus-threads/fork-plus-threads ^M
>       5    <null>                                 /home/simark/build/binutils-gdb/gdb/testsuite/outputs/gdb.threads/fork-plus-threads/fork-plus-threads ^M
>       6    <null>                                 /home/simark/build/binutils-gdb/gdb/testsuite/outputs/gdb.threads/fork-plus-threads/fork-plus-threads ^M
>       7    <null>                                 /home/simark/build/binutils-gdb/gdb/testsuite/outputs/gdb.threads/fork-plus-threads/fork-plus-threads ^M
>       8    <null>                                 /home/simark/build/binutils-gdb/gdb/testsuite/outputs/gdb.threads/fork-plus-threads/fork-plus-threads ^M
>       9    <null>                                 /home/simark/build/binutils-gdb/gdb/testsuite/outputs/gdb.threads/fork-plus-threads/fork-plus-threads ^M
>       10   <null>                                 /home/simark/build/binutils-gdb/gdb/testsuite/outputs/gdb.threads/fork-plus-threads/fork-plus-threads ^M
>       11   <null>                                 /home/simark/build/binutils-gdb/gdb/testsuite/outputs/gdb.threads/fork-plus-threads/fork-plus-threads ^M
>     (gdb) FAIL: gdb.threads/fork-plus-threads.exp: detach-on-fork=off: only inferior 1 left
> 
> when we expect to have just one.  The problem is prune_inferiors not
> pruning inferiors.  And this is caused by all_inferiors_safe not
> actually iterating on inferiors.  The current implementation:
> 
>   inline all_inferiors_safe_range
>   all_inferiors_safe ()
>   {
>     return {};
>   }
> 
> default-constructs an all_inferiors_safe_range, which default-constructs
> an all_inferiors_safe_iterator as its m_begin field, which
> default-constructs a all_inferiors_iterator.  A default-constructed
> all_inferiors_iterator is an end iterator, which means we have
> constructed an (end,end) all_inferiors_safe_range.
> 
> We actually need to pass down the list on which we want to iterator
> (that is the inferior_list global), so that all_inferiors_iterator's
> first constructor is chosen.  We also pass nullptr as the proc_target
> filter.  In this case, we don't do any filtering, but if in the future
> all_inferiors_safe needed to allow filtering on process target (like
> all_inferiors does), we could pass down a process target pointer.
> 
> basic_safe_iterator's constructor needs to be changed to allow
> constructing the wrapped iterator with multiple arguments, not just one.
> 
> With this, gdb.threads/fork-plus-threads.exp is passing once again for
> me.
> 

For me as well.

LGTM.

One suggestion: I'd do
s%/home/simark/build/binutils-gdb/gdb/testsuite/outputs/gdb.threads/fork-plus-threads/fork-plus-threads%fork-plus-threads%
in the log message for readability.

Thanks,
- Tom

> Change-Id: I650552ede596e3590c4b7606ce403690a0278a01
> ---
>  gdb/inferior.h             |  2 +-
>  gdbsupport/safe-iterator.h | 10 +++++-----
>  2 files changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/gdb/inferior.h b/gdb/inferior.h
> index 6662a3bde463..94fbac0fc571 100644
> --- a/gdb/inferior.h
> +++ b/gdb/inferior.h
> @@ -676,7 +676,7 @@ extern intrusive_list<inferior> inferior_list;
>  inline all_inferiors_safe_range
>  all_inferiors_safe ()
>  {
> -  return {};
> +  return all_inferiors_safe_range (nullptr, inferior_list);
>  }
>  
>  /* Returns a range representing all inferiors, suitable to use with
> diff --git a/gdbsupport/safe-iterator.h b/gdbsupport/safe-iterator.h
> index 5cfc5b6ee692..53868d3b3eec 100644
> --- a/gdbsupport/safe-iterator.h
> +++ b/gdbsupport/safe-iterator.h
> @@ -48,11 +48,11 @@ class basic_safe_iterator
>    typedef typename Iterator::iterator_category iterator_category;
>    typedef typename Iterator::difference_type difference_type;
>  
> -  /* Construct using the given argument; the end iterator is default
> -     constructed.  */
> -  template<typename Arg>
> -  explicit basic_safe_iterator (Arg &&arg)
> -    : m_it (std::forward<Arg> (arg)),
> +  /* Construct the begin iterator using the given arguments; the end iterator is
> +     default constructed.  */
> +  template<typename... Args>
> +  explicit basic_safe_iterator (Args &&...args)
> +    : m_it (std::forward<Args> (args)...),
>        m_next (m_it)
>    {
>      if (m_it != m_end)
>