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authorDaniel Baumann <daniel.baumann@progress-linux.org>2024-05-04 12:17:33 +0000
committerDaniel Baumann <daniel.baumann@progress-linux.org>2024-05-04 12:17:33 +0000
commit5e45211a64149b3c659b90ff2de6fa982a5a93ed (patch)
tree739caf8c461053357daa9f162bef34516c7bf452 /doc/src/sgml/html/libpq-cancel.html
parentInitial commit. (diff)
downloadpostgresql-15-5e45211a64149b3c659b90ff2de6fa982a5a93ed.tar.xz
postgresql-15-5e45211a64149b3c659b90ff2de6fa982a5a93ed.zip
Adding upstream version 15.5.upstream/15.5
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
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+<?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>34.7. Canceling Queries in Progress</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="libpq-single-row-mode.html" title="34.6. Retrieving Query Results Row-by-Row" /><link rel="next" href="libpq-fastpath.html" title="34.8. The Fast-Path Interface" /></head><body id="docContent" class="container-fluid col-10"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">34.7. Canceling Queries in Progress</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="libpq-single-row-mode.html" title="34.6. Retrieving Query Results Row-by-Row">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="libpq.html" title="Chapter 34. libpq — C Library">Up</a></td><th width="60%" align="center">Chapter 34. <span class="application">libpq</span> — C Library</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 15.5 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="libpq-fastpath.html" title="34.8. The Fast-Path Interface">Next</a></td></tr></table><hr /></div><div class="sect1" id="LIBPQ-CANCEL"><div class="titlepage"><div><div><h2 class="title" style="clear: both">34.7. Canceling Queries in Progress</h2></div></div></div><a id="id-1.7.3.14.2" class="indexterm"></a><p>
+ A client application can request cancellation of a command that is
+ still being processed by the server, using the functions described in
+ this section.
+
+ </p><div class="variablelist"><dl class="variablelist"><dt id="LIBPQ-PQGETCANCEL"><span class="term"><code class="function">PQgetCancel</code><a id="id-1.7.3.14.3.1.1.1.2" class="indexterm"></a></span></dt><dd><p>
+ Creates a data structure containing the information needed to cancel
+ a command issued through a particular database connection.
+</p><pre class="synopsis">
+PGcancel *PQgetCancel(PGconn *conn);
+</pre><p>
+ </p><p>
+ <a class="xref" href="libpq-cancel.html#LIBPQ-PQGETCANCEL"><code class="function">PQgetCancel</code></a> creates a
+ <code class="structname">PGcancel</code><a id="id-1.7.3.14.3.1.1.2.2.3" class="indexterm"></a> object
+ given a <code class="structname">PGconn</code> connection object. It will return
+ <code class="symbol">NULL</code> if the given <em class="parameter"><code>conn</code></em> is <code class="symbol">NULL</code> or an invalid
+ connection. The <code class="structname">PGcancel</code> object is an opaque
+ structure that is not meant to be accessed directly by the
+ application; it can only be passed to <a class="xref" href="libpq-cancel.html#LIBPQ-PQCANCEL"><code class="function">PQcancel</code></a>
+ or <a class="xref" href="libpq-cancel.html#LIBPQ-PQFREECANCEL"><code class="function">PQfreeCancel</code></a>.
+ </p></dd><dt id="LIBPQ-PQFREECANCEL"><span class="term"><code class="function">PQfreeCancel</code><a id="id-1.7.3.14.3.1.2.1.2" class="indexterm"></a></span></dt><dd><p>
+ Frees a data structure created by <a class="xref" href="libpq-cancel.html#LIBPQ-PQGETCANCEL"><code class="function">PQgetCancel</code></a>.
+</p><pre class="synopsis">
+void PQfreeCancel(PGcancel *cancel);
+</pre><p>
+ </p><p>
+ <a class="xref" href="libpq-cancel.html#LIBPQ-PQFREECANCEL"><code class="function">PQfreeCancel</code></a> frees a data object previously created
+ by <a class="xref" href="libpq-cancel.html#LIBPQ-PQGETCANCEL"><code class="function">PQgetCancel</code></a>.
+ </p></dd><dt id="LIBPQ-PQCANCEL"><span class="term"><code class="function">PQcancel</code><a id="id-1.7.3.14.3.1.3.1.2" class="indexterm"></a></span></dt><dd><p>
+ Requests that the server abandon processing of the current command.
+</p><pre class="synopsis">
+int PQcancel(PGcancel *cancel, char *errbuf, int errbufsize);
+</pre><p>
+ </p><p>
+ The return value is 1 if the cancel request was successfully
+ dispatched and 0 if not. If not, <em class="parameter"><code>errbuf</code></em> is filled
+ with an explanatory error message. <em class="parameter"><code>errbuf</code></em>
+ must be a char array of size <em class="parameter"><code>errbufsize</code></em> (the
+ recommended size is 256 bytes).
+ </p><p>
+ Successful dispatch is no guarantee that the request will have
+ any effect, however. If the cancellation is effective, the current
+ command will terminate early and return an error result. If the
+ cancellation fails (say, because the server was already done
+ processing the command), then there will be no visible result at
+ all.
+ </p><p>
+ <a class="xref" href="libpq-cancel.html#LIBPQ-PQCANCEL"><code class="function">PQcancel</code></a> can safely be invoked from a signal
+ handler, if the <em class="parameter"><code>errbuf</code></em> is a local variable in the
+ signal handler. The <code class="structname">PGcancel</code> object is read-only
+ as far as <a class="xref" href="libpq-cancel.html#LIBPQ-PQCANCEL"><code class="function">PQcancel</code></a> is concerned, so it can
+ also be invoked from a thread that is separate from the one
+ manipulating the <code class="structname">PGconn</code> object.
+ </p></dd></dl></div><p>
+
+ </p><div class="variablelist"><dl class="variablelist"><dt id="LIBPQ-PQREQUESTCANCEL"><span class="term"><code class="function">PQrequestCancel</code><a id="id-1.7.3.14.3.2.1.1.2" class="indexterm"></a></span></dt><dd><p>
+ <a class="xref" href="libpq-cancel.html#LIBPQ-PQREQUESTCANCEL"><code class="function">PQrequestCancel</code></a> is a deprecated variant of
+ <a class="xref" href="libpq-cancel.html#LIBPQ-PQCANCEL"><code class="function">PQcancel</code></a>.
+</p><pre class="synopsis">
+int PQrequestCancel(PGconn *conn);
+</pre><p>
+ </p><p>
+ Requests that the server abandon processing of the current
+ command. It operates directly on the
+ <code class="structname">PGconn</code> object, and in case of failure stores the
+ error message in the <code class="structname">PGconn</code> object (whence it can
+ be retrieved by <a class="xref" href="libpq-status.html#LIBPQ-PQERRORMESSAGE"><code class="function">PQerrorMessage</code></a>). Although
+ the functionality is the same, this approach is not safe within
+ multiple-thread programs or signal handlers, since it is possible
+ that overwriting the <code class="structname">PGconn</code>'s error message will
+ mess up the operation currently in progress on the connection.
+ </p></dd></dl></div><p>
+ </p></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="libpq-single-row-mode.html" title="34.6. Retrieving Query Results Row-by-Row">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="libpq.html" title="Chapter 34. libpq — C Library">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="libpq-fastpath.html" title="34.8. The Fast-Path Interface">Next</a></td></tr><tr><td width="40%" align="left" valign="top">34.6. Retrieving Query Results Row-by-Row </td><td width="20%" align="center"><a accesskey="h" href="index.html" title="PostgreSQL 15.5 Documentation">Home</a></td><td width="40%" align="right" valign="top"> 34.8. The Fast-Path Interface</td></tr></table></div></body></html> \ No newline at end of file
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