Re: [PATCH v2] Associate target_ops with target_fileio file descriptors

Pedro Alves
2015-03-24T16:36:53Z

On 03/24/2015 04:17 PM, Gary Benson wrote:
> Pedro Alves wrote:
>> On 03/20/2015 04:06 PM, Gary Benson wrote:
>>> +
>>> + /* Search for closed handles to reuse. */
>>> + if (lowest_closed_fd >= 0)
>>> + {
>>> + for (index = lowest_closed_fd;
>>> + VEC_iterate (fileio_fh_t, fileio_fhandles, index, fh);
>>> + index++)
>>> + if (is_closed_fileio_fh (fh->fd))
>>> + break;
>>
>> You don't really need 'index'. If this walks using
>> lowest_closed_fd instead, like:
>>
>> for (;
>> VEC_iterate (fileio_fh_t, fileio_fhandles,
>> lowest_closed_fd, fh);
>> lowest_closed_fd++)
>> if (is_closed_fileio_fh (fh->fd))
>> break;
>>
>> Then the next time around we skip slots we already know are
>> open.
>>
>>> + }
>>> +
>>> + /* Push a new handle if no closed handles were found. */
>>> + if (index == total)
>>> + {
>>> + fh = VEC_safe_push (fileio_fh_t, fileio_fhandles, NULL);
>>> + lowest_closed_fd = -1;
>>> + }
>>> +
>>> + /* Fill in the handle and return its index. */
>>> + fh->t = t;
>>> + fh->fd = fd;
>>> +
>>> + return index;
>>> +}
>
> You do need another variable though. The function returns the
> index of the file handle it just used, so you need to save that
> across the bit that sets lowest_closed_fd to -1. I rearranged
> things to this, but it's longer and I'd argue harder to follow:

We can get the index with VEC_address. And if we get rid
of the -1 state, things get event simpler, and release_fileio_fd can
be simplified too, like this (untested):

/* Index into fileio_fhandles of the lowest handle that might be
closed. This permits handle reuse without searching the whole list
each time a new file is opened. */
static int lowest_closed_fd = 0;

static int
acquire_fileio_fd (struct target_ops *t, int fd)
{
fileio_fh_t *fh, buf;

gdb_assert (!is_closed_fileio_fh (fd));

/* Search for closed handles to reuse. */
for (;
VEC_iterate (fileio_fh_t, fileio_fhandles,
lowest_closed_fd, fh);
lowest_closed_fd++)
if (is_closed_fileio_fh (fh->fd))
break;

/* Push a new handle if no closed handles were found. */
if (lowest_closed_fd == VEC_length (fileio_fh_t, fileio_fhandles))
{
fh = VEC_safe_push (fileio_fh_t, fileio_fhandles, NULL);
lowest_closed_fd++;
}

/* Fill in the handle. */
fh->t = t;
fh->fd = fd;

/* Return its index. */
return fh - VEC_address (fileio_fh_t, fileio_fhandles);
}

static void
release_fileio_fd (int fd, fileio_fh_t *fh)
{
fh->fd = -1;
lowest_closed_fd = min (lowest_closed_fd, fd);
}

Thanks,
Pedro Alves