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>41.4. Global Values in PL/Perl</A
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><P
> You can use the global hash <TT
CLASS="VARNAME"
>%_SHARED</TT
> to store
data, including code references, between function calls for the
lifetime of the current session.
</P
><P
> Here is a simple example for shared data:
</P><PRE
CLASS="PROGRAMLISTING"
>CREATE OR REPLACE FUNCTION set_var(name text, val text) RETURNS text AS $$
if ($_SHARED{$_[0]} = $_[1]) {
return 'ok';
} else {
return "cannot set shared variable $_[0] to $_[1]";
}
$$ LANGUAGE plperl;
CREATE OR REPLACE FUNCTION get_var(name text) RETURNS text AS $$
return $_SHARED{$_[0]};
$$ LANGUAGE plperl;
SELECT set_var('sample', 'Hello, PL/Perl! How''s tricks?');
SELECT get_var('sample');</PRE
><P>
</P
><P
> Here is a slightly more complicated example using a code reference:
</P><PRE
CLASS="PROGRAMLISTING"
>CREATE OR REPLACE FUNCTION myfuncs() RETURNS void AS $$
$_SHARED{myquote} = sub {
my $arg = shift;
$arg =~ s/(['\\])/\\$1/g;
return "'$arg'";
};
$$ LANGUAGE plperl;
SELECT myfuncs(); /* initializes the function */
/* Set up a function that uses the quote function */
CREATE OR REPLACE FUNCTION use_quote(TEXT) RETURNS text AS $$
my $text_to_quote = shift;
my $qfunc = $_SHARED{myquote};
return &$qfunc($text_to_quote);
$$ LANGUAGE plperl;</PRE
><P>
(You could have replaced the above with the one-liner
<TT
CLASS="LITERAL"
>return $_SHARED{myquote}->($_[0]);</TT
>
at the expense of readability.)
</P
><P
> For security reasons, PL/Perl executes functions called by any one SQL role
in a separate Perl interpreter for that role. This prevents accidental or
malicious interference by one user with the behavior of another user's
PL/Perl functions. Each such interpreter has its own value of the
<TT
CLASS="VARNAME"
>%_SHARED</TT
> variable and other global state. Thus, two
PL/Perl functions will share the same value of <TT
CLASS="VARNAME"
>%_SHARED</TT
>
if and only if they are executed by the same SQL role. In an application
wherein a single session executes code under multiple SQL roles (via
<TT
CLASS="LITERAL"
>SECURITY DEFINER</TT
> functions, use of <TT
CLASS="COMMAND"
>SET ROLE</TT
>, etc)
you may need to take explicit steps to ensure that PL/Perl functions can
share data via <TT
CLASS="VARNAME"
>%_SHARED</TT
>. To do that, make sure that
functions that should communicate are owned by the same user, and mark
them <TT
CLASS="LITERAL"
>SECURITY DEFINER</TT
>. You must of course take care that
such functions can't be used to do anything unintended.
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