DirectFunctionCall not executing for a function in the same file

Question

In Apache AGE, when I call the DirectFunctionCall() function. It doesn't get executed. I have tried putting logging statements using elog() function in the write() function. But, it's of no use. The code sample is given below -

PG_FUNCTION_INFO_V1(some_function);

PG_FUNCTION_INFO_V1(write);

Datum
some_function(PG_FUNCTION_ARGS) {
    .
    .
    .
    DirectFunctionCall4(write, dest_lob, 2 * size, dest_offset, cstring_to_text(buffer));
}

The write function mentioned here is defined below in the same file. I have checked the parameters, as well as the return type. Everything is matching correctly but still the statement is not executed.

Answer 1

Based on your code snippet, changing the order of the function info definitions should work. The dependent function should be defined after the base function.

PG_FUNCTION_INFO_V1(write);
PG_FUNCTION_INFO_V1(some_function);

But there is a better way to achieve the same functionality. Generally, if you want to call the same piece of code for many functions, it is advisable to make it a separate module( in this case a separate function)

The best way to deal with this case in Postgres extensions in the c code - is to not use direct function calls within the same file.

Instead, create a static helper function (write_helper) and make the PG function write a wrapper function that calls this function.

PG_FUNCTION_INFO_V1(write);
PG_FUNCTION_INFO_V1(some_function);

static <return_type> write_helper(<parameters>);

// wrapper function for the write_helper function
Datum
write(PG_FUNCTION_ARGS){
   <return_value type> result;
   result = write_helper(<parameters>);
   .
   .
   .

}

Datum
some_function(PG_FUNCTION_ARGS) {
    .
    .
    .
    write_helper(<parameters>);
    .
    .
    .
}

// define the static function
static 
<return_type> write_helper(<parameters>){
     returns <return value>
}