Get last generated serial sequence and set it up when explicit value is used

Hi all!

Using SERIAL or BIGSERIAL column, I try to find a smart solution to
do the following when an INSERT is done:

1) Retrieve the last generated sequence, so the program can use it.

2) Setup the underlying sequence, if an explicit value was used by
the INSERT statement.

So far I figured out the following by using the RETURNING clause...

Is this ok / legal / without risk? (when multiple users insert rows at the same time?)

test1=# create table table1 ( pkey serial not null primary key, name varchar(50) );
CREATE TABLE

test1=# insert into table1 (name) values ('aaaa') returning pkey, (select last_value from table1_pkey_seq);
pkey | last_value
------+------------
1 | 1
(1 row)

INSERT 0 1

test1=# insert into table1 (name) values ('aaaa') returning pkey, (select last_value from table1_pkey_seq);
pkey | last_value
------+------------
2 | 2
(1 row)

INSERT 0 1

test1=# insert into table1 (pkey,name) values (100,'aaaa') returning pkey, (select last_value from table1_pkey_seq);
pkey | last_value
------+------------
100 | 2
(1 row)

INSERT 0 1

I see 100 is > than 2, so reset the sequence:

test1=# select setval('table1_pkey_seq',101,false);
setval
--------
101
(1 row)

test1=# insert into table1 (name) values ('aaaa') returning pkey, (select last_value from table1_pkey_seq);
pkey | last_value
------+------------
101 | 101
(1 row)

INSERT 0 1

Any better way to do that in a single SQL statement?

Is it legal to use a subquery in a RETURNING clause?

Thanks!
Seb