Transaction control in a C language function

Hello all,

I would like to implement transaction control in a function implemented in
C language. Currently I'm using SPI to do the job.
When calling SPI_commit() it returns this error message:
SQL Error [XX000]: ERROR: portal snapshots (0) did not account for all
active snapshots (1)
Below, there is an example.

PG_FUNCTION_INFO_V1(my_commit);

Datum my_commit(PG_FUNCTION_ARGS)
{
SPIExecuteOptions execopts;

SPI_connect_ext(SPI_OPT_NONATOMIC);

memset(&execopts, 0, sizeof(execopts));
execopts.params = NULL;
execopts.read_only = false;
execopts.allow_nonatomic = true;
execopts.must_return_tuples = false;
execopts.tcount = 0;
execopts.dest = NULL;
execopts.owner = NULL;

/* Execute some SQL commands */
SPI_execute_extended("UPDATE mytable SET name = 'done'", &execopts);

/* Commit the transaction */
SPI_commit();

SPI_finish();

PG_RETURN_NULL();
}

Thanks in advance,
Flaris Feller