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diff --git a/doc/src/sgml/html/pltcl-global.html b/doc/src/sgml/html/pltcl-global.html new file mode 100644 index 0000000..38ee06d --- /dev/null +++ b/doc/src/sgml/html/pltcl-global.html @@ -0,0 +1,45 @@ +<?xml version="1.0" encoding="UTF-8" standalone="no"?> +<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>44.4. Global Data in PL/Tcl</title><link rel="stylesheet" type="text/css" href="stylesheet.css" /><link rev="made" href="pgsql-docs@lists.postgresql.org" /><meta name="generator" content="DocBook XSL Stylesheets Vsnapshot" /><link rel="prev" href="pltcl-data.html" title="44.3. Data Values in PL/Tcl" /><link rel="next" href="pltcl-dbaccess.html" title="44.5. Database Access from PL/Tcl" /></head><body id="docContent" class="container-fluid col-10"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">44.4. Global Data in PL/Tcl</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="pltcl-data.html" title="44.3. Data Values in PL/Tcl">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="pltcl.html" title="Chapter 44. PL/Tcl — Tcl Procedural Language">Up</a></td><th width="60%" align="center">Chapter 44. PL/Tcl — Tcl Procedural Language</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 15.4 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="pltcl-dbaccess.html" title="44.5. Database Access from PL/Tcl">Next</a></td></tr></table><hr /></div><div class="sect1" id="PLTCL-GLOBAL"><div class="titlepage"><div><div><h2 class="title" style="clear: both">44.4. Global Data in PL/Tcl</h2></div></div></div><a id="id-1.8.9.8.2" class="indexterm"></a><p> + Sometimes it + is useful to have some global data that is held between two + calls to a function or is shared between different functions. + This is easily done in PL/Tcl, but there are some restrictions that + must be understood. + </p><p> + For security reasons, PL/Tcl executes functions called by any one SQL + role in a separate Tcl interpreter for that role. This prevents + accidental or malicious interference by one user with the behavior of + another user's PL/Tcl functions. Each such interpreter will have its own + values for any <span class="quote">“<span class="quote">global</span>”</span> Tcl variables. Thus, two PL/Tcl + functions will share the same global variables 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 <code class="literal">SECURITY + DEFINER</code> functions, use of <code class="command">SET ROLE</code>, etc.) you may need to + take explicit steps to ensure that PL/Tcl functions can share data. To + do that, make sure that functions that should communicate are owned by + the same user, and mark them <code class="literal">SECURITY DEFINER</code>. You must of + course take care that such functions can't be used to do anything + unintended. + </p><p> + All PL/TclU functions used in a session execute in the same Tcl + interpreter, which of course is distinct from the interpreter(s) + used for PL/Tcl functions. So global data is automatically shared + between PL/TclU functions. This is not considered a security risk + because all PL/TclU functions execute at the same trust level, + namely that of a database superuser. + </p><p> + To help protect PL/Tcl functions from unintentionally interfering + with each other, a global + array is made available to each function via the <code class="function">upvar</code> + command. The global name of this variable is the function's internal + name, and the local name is <code class="literal">GD</code>. It is recommended that + <code class="literal">GD</code> be used + for persistent private data of a function. Use regular Tcl global + variables only for values that you specifically intend to be shared among + multiple functions. (Note that the <code class="literal">GD</code> arrays are only + global within a particular interpreter, so they do not bypass the + security restrictions mentioned above.) + </p><p> + An example of using <code class="literal">GD</code> appears in the + <code class="function">spi_execp</code> example below. + </p></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="pltcl-data.html" title="44.3. Data Values in PL/Tcl">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="pltcl.html" title="Chapter 44. PL/Tcl — Tcl Procedural Language">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="pltcl-dbaccess.html" title="44.5. Database Access from PL/Tcl">Next</a></td></tr><tr><td width="40%" align="left" valign="top">44.3. 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