From: Pedro Alves <palves@redhat.com>
To: Sergio Durigan Junior <sergiodj@redhat.com>
Cc: Simon Marchi <simon.marchi@polymtl.ca>,
GDB Patches <gdb-patches@sourceware.org>
Subject: Re: [PATCH v6] C++ify gdb/common/environ.c
Date: Mon, 19 Jun 2017 18:09:00 -0000 [thread overview]
Message-ID: <1e62abc1-ab02-65dd-f520-27120be033b8@redhat.com> (raw)
In-Reply-To: <87tw3bx3i4.fsf@redhat.com>
On 06/19/2017 06:59 PM, Sergio Durigan Junior wrote:
> On Monday, June 19 2017, Pedro Alves wrote:
>
>> On 06/19/2017 05:26 PM, Simon Marchi wrote:
>>> On 2017-06-19 17:44, Pedro Alves wrote:
>>>> If we take the "always push a NULL on construction" approach, and
>>>> we want moved-from gdb_environs to be valid, then yes. Note how this
>>>> results in extra heap allocations when e.g., returning a
>>>> gdb_environ from functions by value, and makes std::vector<gdb_environ>
>>>> much less efficient when it decides it needs to reallocate/move
>>>> elements. Representing the empty state with a cleared internal
>>>> vector would avoid this.
>>>
>>> Given the move case, since the goal is to be efficient, then yeah I
>>> would agree
>>> that it would make sense to make a little bit of efforts to avoid
>>> allocating
>>> memory for an objects we are almost certainly throwing away.
>>>
>>> But still, in order to leave environ objects in a valid state after a
>>> move and
>>> to pedantically comply with the STL spec which says that the vector is
>>> left in
>>> an unspecified state, shouldn't we do a .clear () on the moved-from
>>> vector after
>>> the move?
>>
>> See accepted answer at:
>>
>> https://stackoverflow.com/questions/17730689/is-a-moved-from-vector-always-empty
>>
>> So the only case where it'd be needed would be in op=, and iff the
>> vectors had different allocators, which is not the case here.
>> So no, it's not necessary. But I'd be fine with calling it.
>>
>>>
>>>> Note BTW, that we need to be careful with self-move leaving the
>>>> *this object in a valid state.
>>>
>>> Should we just do
>>>
>>> if (&other == this)
>>> return *this;
>>
>> Might not be necessary if without that the object ends up
>> valid anyway. But what you wrote is a safe bet.
>
> So, what do you guys think about the patch below, which applies on top
> of the original?
Missed fixing move ctor?
+ /* Move constructor. */
+ gdb_environ (gdb_environ &&e)
+ : m_environ_vector (std::move (e.m_environ_vector))
+ {}
Thanks,
Pedro Alves
next prev parent reply other threads:[~2017-06-19 18:09 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-04-13 4:05 [PATCH] " Sergio Durigan Junior
2017-04-15 18:51 ` [PATCH v2] " Sergio Durigan Junior
2017-04-15 21:22 ` Simon Marchi
2017-04-18 2:49 ` Sergio Durigan Junior
2017-04-16 5:09 ` Simon Marchi
2017-04-16 17:32 ` Sergio Durigan Junior
2017-04-18 3:03 ` [PATCH v3] " Sergio Durigan Junior
2017-04-19 4:56 ` Simon Marchi
2017-04-19 16:30 ` Pedro Alves
2017-04-19 18:14 ` Pedro Alves
2017-05-01 2:22 ` Sergio Durigan Junior
2017-05-04 15:30 ` Pedro Alves
2017-06-14 19:22 ` [PATCH v4] " Sergio Durigan Junior
2017-06-16 15:45 ` Pedro Alves
2017-06-16 18:01 ` Sergio Durigan Junior
2017-06-16 18:23 ` Pedro Alves
2017-06-16 21:59 ` Sergio Durigan Junior
2017-06-16 22:23 ` [PATCH v5] " Sergio Durigan Junior
2017-06-17 8:54 ` Simon Marchi
2017-06-19 4:19 ` Sergio Durigan Junior
2017-06-19 13:40 ` Pedro Alves
2017-06-19 16:19 ` Sergio Durigan Junior
2017-06-19 12:13 ` Pedro Alves
2017-06-20 14:02 ` Pedro Alves
2017-06-19 4:36 ` [PATCH v6] " Sergio Durigan Junior
2017-06-19 4:51 ` Sergio Durigan Junior
2017-06-19 7:18 ` Simon Marchi
2017-06-19 14:26 ` Pedro Alves
2017-06-19 15:30 ` Simon Marchi
2017-06-19 15:44 ` Pedro Alves
2017-06-19 15:47 ` Pedro Alves
2017-06-19 16:26 ` Simon Marchi
2017-06-19 16:55 ` Pedro Alves
2017-06-19 17:59 ` Sergio Durigan Junior
2017-06-19 18:09 ` Pedro Alves [this message]
2017-06-19 18:23 ` Sergio Durigan Junior
2017-06-19 18:36 ` Pedro Alves
2017-06-19 18:38 ` Pedro Alves
2017-06-19 14:26 ` Pedro Alves
2017-06-19 16:13 ` Sergio Durigan Junior
2017-06-19 16:38 ` Pedro Alves
2017-06-19 16:46 ` Sergio Durigan Junior
2017-06-19 18:27 ` [PATCH v7] " Sergio Durigan Junior
2017-06-20 3:27 ` [PATCH v8] " Sergio Durigan Junior
2017-06-20 12:13 ` Pedro Alves
2017-06-20 12:46 ` Simon Marchi
2017-06-20 13:00 ` Sergio Durigan Junior
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