Thread: C function returns null values

C function returns null values

From

Gregor Trefs

Date:

15 July 2011, 08:55:30

Hello all,

I developed a C function which returns a record. The record contains 3 scalar values and 2 arrays. Randomly some record elements are null and I wonder why. I could trace down the problem to the point where the return record is created. Until this point everything is computed correctly. Below you see an excerpt of the relevant code. I use PostGres 8.4 on Ubuntu 10.10 (x64).

typedef struct {

// Size of the array

int size;

// Values of the array

double *values;

} array_d;

// Integer

typedef struct {

// Size of the array

int size;

// Values of the array

int *values;

} array_i;

typedef struct {

interval_orders o;

array_d *interval_weights;

array_d *interval_borders;

array_i *add_weights;

double b;

} c_param_type;

void create_dati_from_result(Datum *values, c_param_type *param) {

// Array creation

ArrayType *weights, *borders;

Datum *weights_elem;

Datum *borders_elem;

int16 typlen;

bool typbyval;

char typalign;

int i;

// Set values

values[0] = Float8GetDatum(param->o.interval_weight);

values[1] = Float8GetDatum(param->o.quantitiy);

values[2] = Float8GetDatum(param->o.long_sql);

// Create datum arrays

weights_elem = palloc(param->interval_weights->size * sizeof (Datum));

borders_elem = palloc(param->interval_borders->size * sizeof (Datum));

for (i = 0; i < param->interval_weights->size; i++) {

weights_elem[i] = Float8GetDatum((float8) param->interval_weights->values[i]);

}

for (i = 0; i < param->interval_borders->size; i++) {

borders_elem[i] = Float8GetDatum((float8) param->interval_borders->values[i]);

}

// Create array type

get_typlenbyvalalign(FLOAT8OID, &typlen, &typbyval, &typalign);

weights = construct_array(weights_elem, param->interval_weights->size, FLOAT8OID, typlen, typbyval, typalign);

borders = construct_array(borders_elem, param->interval_borders->size, FLOAT8OID, typlen, typbyval, typalign);

values[3] = PointerGetDatum(borders);

values[4] = PointerGetDatum(weights);

}

PG_FUNCTION_INFO_V1(insert_order);

Datum insert_order(PG_FUNCTION_ARGS) {

// Variable declarations go here

// …

// vars for result

TupleDesc tupdesc;

Datum *values;

bool *nulls;

int tuplen,i;

HeapTuple res_tuple;

// Look whether everything has been provided

if (PG_ARGISNULL(0)) {

ereport(ERROR, (errcode(ERRCODE_NULL_VALUE_NOT_ALLOWED), errmsg("First argument is NULL")));

PG_RETURN_NULL();

}

// Allocate memory

param = palloc(sizeof (c_param_type));

// Get the HeapTupleHeader

header = PG_GETARG_HEAPTUPLEHEADER_COPY(0);

// Extract information from parameter

if (!extract_information(param, header)) {

PG_RETURN_NULL();

}

// Some more code goes here

// …

// Set values

param->o.long_sql = total_cost;

param->o.quantitiy = weight;

param->o.interval_weight = weight;

// Create result tuple

values = palloc(sizeof(Datum)*5);

if (get_call_result_type(fcinfo, NULL, &tupdesc) != TYPEFUNC_COMPOSITE)

ereport(ERROR, (errcode(ERRCODE_SUCCESSFUL_COMPLETION), errmsg("function returning record called in context that cannot accept type record")));

// Get Dati

create_dati_from_result(values, param);

// Init Tuple Desc

tupdesc = BlessTupleDesc(tupdesc);

// Size

tuplen = tupdesc->natts;

// Allocate enough memory for nulls

nulls = palloc(tuplen * sizeof (bool));

// Create tuple

res_tuple = heap_form_tuple(tupdesc, values, nulls);

// Free allocated memory

pfree(nulls);

// Return result

PG_RETURN_DATUM(HeapTupleGetDatum(res_tuple));

}

I hope you can help me.

Regards,

Gregor

Re: C function returns null values

From

Tom Lane

Date:

15 July 2011, 14:24:33

Gregor Trefs <gregor.trefs@delphit.com> writes:
> I developed a C function which returns a record. The record contains 3 scalar values and 2 arrays. Randomly some
recordelements are null and I wonder why. I could trace down the problem to the point where the return record is
created.Until this point everything is computed correctly. Below you see an excerpt of the relevant code. I use
PostGres8.4 on Ubuntu 10.10 (x64). 

You're not bothering to fill in the nulls[] array:

>     // Allocate enough memory for nulls
>     nulls = palloc(tuplen * sizeof (bool));
>     // Create tuple
>     res_tuple = heap_form_tuple(tupdesc, values, nulls);

palloc0 would work better here.

BTW, it's a good idea to develop/test C code in a backend built with
--enable-debug --enable-cassert.  Had you been doing so, palloc would
have given you back intentionally-garbage-filled memory, and you'd have
noticed the mistake immediately.

            regards, tom lane

Re: C function returns null values

From

Gregor Trefs

Date:

18 July 2011, 14:08:45

Thanks for your answer. I edited my code, but still get these random null values. What else can I do ?

Regards

-----Ursprüngliche Nachricht-----
Von: Tom Lane [mailto:tgl@sss.pgh.pa.us]
Gesendet: Freitag, 15. Juli 2011 16:24
An: Gregor Trefs
Cc: pgsql-general@postgresql.org
Betreff: Re: [GENERAL] C function returns null values

Gregor Trefs <gregor.trefs@delphit.com> writes:
> I developed a C function which returns a record. The record contains 3 scalar values and 2 arrays. Randomly some
recordelements are null and I wonder why. I could trace down the problem to the point where the return record is
created.Until this point everything is computed correctly. Below you see an excerpt of the relevant code. I use
PostGres8.4 on Ubuntu 10.10 (x64). 

You're not bothering to fill in the nulls[] array:

>     // Allocate enough memory for nulls
>     nulls = palloc(tuplen * sizeof (bool));
>     // Create tuple
>     res_tuple = heap_form_tuple(tupdesc, values, nulls);

palloc0 would work better here.

BTW, it's a good idea to develop/test C code in a backend built with --enable-debug --enable-cassert.  Had you been
doingso, palloc would have given you back intentionally-garbage-filled memory, and you'd have noticed the mistake
immediately.

            regards, tom lane

Re: C function returns null values

From

Tom Lane

Date:

18 July 2011, 14:32:51

Gregor Trefs <gregor.trefs@delphit.com> writes:
> Thanks for your answer. I edited my code, but still get these random null values. What else can I do ?

Mph ... you're aware that you have to start a fresh session to load a
new version of a .so into the backend?

            regards, tom lane

Re: C function returns null values

From

Gregor Trefs

Date:

18 July 2011, 15:25:13

Well, yes. I wrote a little make file which takes care of this part (except restarting the session):

INCLUDEDIRS += -I$(shell pg_config --includedir-server)
LIBDIR = -L$(shell pg_config --libdir)
LIBINSTALL = $(shell pg_config --pkglibdir)

integrated_c.so: integrated_c.c Makefile
            gcc -fpic -o integrated_c.o -c integrated_c.c $(INCLUDEDIRS)
            gcc -shared -o integrated_c.so integrated_c.o $(LIBDIR) -lmpfr -lgmp
            cp integrated_c.so $(LIBINSTALL)

-----Ursprüngliche Nachricht-----
Von: Tom Lane [mailto:tgl@sss.pgh.pa.us]
Gesendet: Montag, 18. Juli 2011 16:33
An: Gregor Trefs
Cc: pgsql-general@postgresql.org
Betreff: Re: [GENERAL] C function returns null values

Gregor Trefs <gregor.trefs@delphit.com> writes:
> Thanks for your answer. I edited my code, but still get these random null values. What else can I do ?

Mph ... you're aware that you have to start a fresh session to load a new version of a .so into the backend?

            regards, tom lane

Re: C function returns null values

From

Gregor Trefs

Date:

19 July 2011, 15:18:09

Finally I got it working. You were right Tom Lane. I actually did not copy the corrected source file onto the server
andthus still had this "mysterious" failure. So, palloc0 is the solution. Thanks again. 

Regards,
Gregor Trefs

-----Ursprüngliche Nachricht-----
Von: pgsql-general-owner@postgresql.org [mailto:pgsql-general-owner@postgresql.org] Im Auftrag von Gregor Trefs
Gesendet: Montag, 18. Juli 2011 17:20
Cc: pgsql-general@postgresql.org
Betreff: Re: [GENERAL] C function returns null values

Well, yes. I wrote a little make file which takes care of this part (except restarting the session):

INCLUDEDIRS += -I$(shell pg_config --includedir-server) LIBDIR = -L$(shell pg_config --libdir) LIBINSTALL = $(shell
pg_config--pkglibdir) 

integrated_c.so: integrated_c.c Makefile
            gcc -fpic -o integrated_c.o -c integrated_c.c $(INCLUDEDIRS)
            gcc -shared -o integrated_c.so integrated_c.o $(LIBDIR) -lmpfr -lgmp
            cp integrated_c.so $(LIBINSTALL)

-----Ursprüngliche Nachricht-----
Von: Tom Lane [mailto:tgl@sss.pgh.pa.us]
Gesendet: Montag, 18. Juli 2011 16:33
An: Gregor Trefs
Cc: pgsql-general@postgresql.org
Betreff: Re: [GENERAL] C function returns null values

Gregor Trefs <gregor.trefs@delphit.com> writes:
> Thanks for your answer. I edited my code, but still get these random null values. What else can I do ?

Mph ... you're aware that you have to start a fresh session to load a new version of a .so into the backend?

            regards, tom lane

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