Re: [PATCH 2/6] Use vector in remote-fileio.c

Lancelot SIX
2024-01-01T14:21:18Z

Hi Tom,

I have a couple of comments below.

On Sun, Dec 31, 2023 at 01:25:39PM -0700, Tom Tromey wrote:
> This changes remote_fio_data to be an object holding a vector. This
> simplifies the code somewhat.
> ---
> gdb/remote-fileio.c | 51 +++++++++++++++++----------------------------------
> 1 file changed, 17 insertions(+), 34 deletions(-)
>
> diff --git a/gdb/remote-fileio.c b/gdb/remote-fileio.c
> index 367edb54f74..4891b0c5b92 100644
> --- a/gdb/remote-fileio.c
> +++ b/gdb/remote-fileio.c
> @@ -37,9 +37,9 @@
> #endif
> #include <signal.h>
>
> -static struct {
> - int *fd_map;
> - int fd_map_size;
> +static struct
> +{
> + std::vector<int> fd_map;
> } remote_fio_data;
>
> #define FIO_FD_INVALID -1
> @@ -51,16 +51,13 @@ static int remote_fio_system_call_allowed = 0;
> static int
> remote_fileio_init_fd_map (void)
> {
> - int i;
> -
> - if (!remote_fio_data.fd_map)
> + if (remote_fio_data.fd_map.empty ())
> {
> - remote_fio_data.fd_map = XNEWVEC (int, 10);
> - remote_fio_data.fd_map_size = 10;
> + remote_fio_data.fd_map.resize (10);
> remote_fio_data.fd_map[0] = FIO_FD_CONSOLE_IN;
> remote_fio_data.fd_map[1] = FIO_FD_CONSOLE_OUT;
> remote_fio_data.fd_map[2] = FIO_FD_CONSOLE_OUT;
> - for (i = 3; i < 10; ++i)
> + for (int i = 3; i < 10; ++i)
> remote_fio_data.fd_map[i] = FIO_FD_INVALID;

std::vector<T, Alloc>::resize has an overload which takes a value to use
for new elements of the vector. This could be simplified as

remote_fio_data.fd_map.resize (10, FIO_FD_INVALID);
remote_fio_data.fd_map[0] = FIO_FD_CONSOLE_IN;
remote_fio_data.fd_map[1] = FIO_FD_CONSOLE_OUT;
remote_fio_data.fd_map[2] = FIO_FD_CONSOLE_OUT;

See below, but overall, I don’t really think we need to keep the "grow
by 10" strategy when using std::vector, this could simply be

remote_fio_data.fd_map.emplace_back (FIO_FD_CONSOLE_IN)
remote_fio_data.fd_map.emplace_back (FIO_FD_CONSOLE_OUT)
remote_fio_data.fd_map.emplace_back (FIO_FD_CONSOLE_OUT)

> }
> return 3;
> @@ -69,25 +66,20 @@ remote_fileio_init_fd_map (void)
> static int
> remote_fileio_resize_fd_map (void)
> {
> - int i = remote_fio_data.fd_map_size;
> -
> - if (!remote_fio_data.fd_map)
> + if (remote_fio_data.fd_map.empty ())
> return remote_fileio_init_fd_map ();
> - remote_fio_data.fd_map_size += 10;
> - remote_fio_data.fd_map =
> - (int *) xrealloc (remote_fio_data.fd_map,
> - remote_fio_data.fd_map_size * sizeof (int));
> - for (; i < remote_fio_data.fd_map_size; i++)
> +
> + int i = remote_fio_data.fd_map.size ();
> + remote_fio_data.fd_map.resize (i + 10);
> + for (; i < remote_fio_data.fd_map.size (); i++)
> remote_fio_data.fd_map[i] = FIO_FD_INVALID;

Similarly, if you keep the "grow by 10" strategy this could be

remote_fio_data.fd_map.resize (i + 10, FIO_FD_INVALID);

> - return remote_fio_data.fd_map_size - 10;
> + return remote_fio_data.fd_map.size () - 10;
> }
>
> static int
> remote_fileio_next_free_fd (void)
> {
> - int i;
> -
> - for (i = 0; i < remote_fio_data.fd_map_size; ++i)
> + for (int i = 0; i < remote_fio_data.fd_map.size (); ++i)
> if (remote_fio_data.fd_map[i] == FIO_FD_INVALID)
> return i;

I think that’s mostly a personal preference thing, but std::find could
be used instead of an explicit loop

auto it = std::find (remote_fio_data.fd_map.begin (),
remote_fio_data.fd_map.end (),
FIO_FD_INVALID);
if (it != remote_fio_data.fd_map.end ())
return std::distance (remote_fio_data.fd_map.begin (), it);
return remote_fileio_resize_fd_map ();

I think it could be possible to go one step further and remove
remote_fileio_resize_fd_map entirely. The "grow by 10" strategy is not
necessary anymore if you use a std::vector. A similar allocation
strategies comes for free.

static int
remote_fileio_next_free_fd ()
{
auto it = std::find (remote_fio_data.fd_map.begin (),
remote_fio_data.fd_map.end (),
FIO_FD_INVALID);
if (it != remote_fio_data.fd_map.end ())
return std::ditance (remote_fio_data.fd_map.begin (), it);

remote_fio_data.fd_map.emplace_back (FIO_FD_INVALID);
return remote_fio_data.fd_map.size () - 1;
}

One could also inline this inside remote_fileio_map_fd, and directly set
the appropriate FD value instead of using FIO_FD_INVALID temporarily.
But I would be happy keeping things this way for readability.

Best,
Lancelot.

> return remote_fileio_resize_fd_map ();
> @@ -106,7 +98,7 @@ static int
> remote_fileio_map_fd (int target_fd)
> {
> remote_fileio_init_fd_map ();
> - if (target_fd < 0 || target_fd >= remote_fio_data.fd_map_size)
> + if (target_fd < 0 || target_fd >= remote_fio_data.fd_map.size ())
> return FIO_FD_INVALID;
> return remote_fio_data.fd_map[target_fd];
> }
> @@ -115,7 +107,7 @@ static void
> remote_fileio_close_target_fd (int target_fd)
> {
> remote_fileio_init_fd_map ();
> - if (target_fd >= 0 && target_fd < remote_fio_data.fd_map_size)
> + if (target_fd >= 0 && target_fd < remote_fio_data.fd_map.size ())
> remote_fio_data.fd_map[target_fd] = FIO_FD_INVALID;
> }
>
> @@ -1147,21 +1139,12 @@ do_remote_fileio_request (remote_target *remote, char *buf)
> void
> remote_fileio_reset (void)
> {
> - int ix;
> -
> - for (ix = 0; ix != remote_fio_data.fd_map_size; ix++)
> + for (int fd : remote_fio_data.fd_map)
> {
> - int fd = remote_fio_data.fd_map[ix];
> -
> if (fd >= 0)
> close (fd);
> }
> - if (remote_fio_data.fd_map)
> - {
> - xfree (remote_fio_data.fd_map);
> - remote_fio_data.fd_map = NULL;
> - remote_fio_data.fd_map_size = 0;
> - }
> + remote_fio_data.fd_map.clear ();
> }
>
> /* Handle a file I/O request. BUF points to the packet containing the
>
> --
> 2.43.0
>