Re: I propose killing PL/Tcl's "modules" infrastructure

On 02/25/2017 01:44 PM, Tom Lane wrote:
> Andrew Dunstan <andrew(dot)dunstan(at)2ndquadrant(dot)com> writes:
>> On 02/25/2017 01:14 PM, Tom Lane wrote:
>>> Now, we could try to fix this bug, and add the regression test coverage
>>> that the code clearly lacks, and upgrade the documentation about it from
>>> its currently very sad state. But I think the right answer is just to
>>> remove the feature altogether. It's evidently not being used, and it's
>>> kind of insecure by design, and it would not be that hard for someone
>>> to provide equivalent functionality entirely in userland if they really
>>> wanted it.
>> In PLv8 we added a parameter plv8.start_proc that names a parameterless
>> function that's executed when plv8 is first called in each session. It
>> can be used quite easily to implement something like a modules
>> infrastructure - in fact I have used it to good effect for exactly that.
>> Maybe something similar for pltcl would be a good thing.
> Yeah, the only part that's even a bit hard to replicate in userland is
> initializing the autoloading mechanism in each session. It would be
> cleaner to provide a feature similar to what you describe that could
> be used for that purpose as well as others. However, where does the
> "parameterless function" come from? Is it a regular PLv8 (or for this
> purpose PL/Tcl) function expected to be present in pg_proc?
>
>

Yes, it's a regular PLv8 function.Here's an example. It presupposes that
there is a table called plv8_modules (modname text, code text,
load_on_start boolean).

CREATE OR REPLACE FUNCTION public.plv8_startup()
RETURNS void
LANGUAGE plv8
AS $function$
if (typeof plv8_loaded_modules == 'undefined')
plv8_loaded_modules = {};
load_module = function(modname)
{
if (plv8_loaded_modules[modname])
return;
var rows = plv8.execute("SELECT code from plv8_modules " +
" where modname = $1", [modname]);
for (var r = 0; r < rows.length; r++)
{
var code = rows[r].code;
eval("(function() { " + code + "})")();
// plv8.elog(NOTICE,"loaded module " + modname);
plv8_loaded_modules[modname] = 1;
}

};
reload_module = function(modname)
{
var rows = plv8.execute("SELECT code from plv8_modules " +
" where modname = $1", [modname]);
for (var r = 0; r < rows.length; r++)
{
var code = rows[r].code;
eval("(function() { " + code + "})")();
// plv8.elog(NOTICE,"loaded module " + modname);
plv8_loaded_modules[modname] = 1;
}

};

var rows = plv8.execute("SELECT modname, code from plv8_modules
where load_on_start");
for (var r = 0; r < rows.length; r++)
{
var modname = rows[r].modname;
if (plv8_loaded_modules[modname])
continue;
var code = rows[r].code;
eval("(function() { " + code + "})")();
plv8_loaded_modules[modname] = 1;
// plv8.elog(NOTICE,"loaded module " + modname);
};
$function$;

cheers

andrew

--
Andrew Dunstan https://www.2ndQuadrant.com
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