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diff --git a/www/c3ref/busy_handler.html b/www/c3ref/busy_handler.html new file mode 100644 index 0000000..7adcc6f --- /dev/null +++ b/www/c3ref/busy_handler.html @@ -0,0 +1,184 @@ +<!DOCTYPE html> +<html><head> +<meta name="viewport" content="width=device-width, initial-scale=1.0"> +<meta http-equiv="content-type" content="text/html; charset=UTF-8"> +<link href="../sqlite.css" rel="stylesheet"> +<title>Register A Callback To Handle SQLITE_BUSY Errors</title> +<!-- path=../ --> +</head> +<body> +<div class=nosearch> +<a href="../index.html"> +<img class="logo" src="../images/sqlite370_banner.gif" alt="SQLite" border="0"> +</a> +<div><!-- IE hack to prevent disappearing logo --></div> +<div class="tagline desktoponly"> +Small. Fast. Reliable.<br>Choose any three. +</div> +<div class="menu mainmenu"> +<ul> +<li><a href="../index.html">Home</a> +<li class='mobileonly'><a href="javascript:void(0)" onclick='toggle_div("submenu")'>Menu</a> +<li class='wideonly'><a href='../about.html'>About</a> +<li class='desktoponly'><a href="../docs.html">Documentation</a> +<li class='desktoponly'><a href="../download.html">Download</a> +<li class='wideonly'><a href='../copyright.html'>License</a> +<li class='desktoponly'><a href="../support.html">Support</a> +<li class='desktoponly'><a href="../prosupport.html">Purchase</a> +<li class='search' id='search_menubutton'> +<a href="javascript:void(0)" onclick='toggle_search()'>Search</a> +</ul> +</div> +<div class="menu submenu" id="submenu"> +<ul> +<li><a href='../about.html'>About</a> +<li><a href='../docs.html'>Documentation</a> +<li><a href='../download.html'>Download</a> +<li><a href='../support.html'>Support</a> +<li><a href='../prosupport.html'>Purchase</a> +</ul> +</div> +<div class="searchmenu" id="searchmenu"> +<form method="GET" action="../search"> +<select name="s" id="searchtype"> +<option value="d">Search Documentation</option> +<option value="c">Search Changelog</option> +</select> +<input type="text" name="q" id="searchbox" value=""> +<input type="submit" value="Go"> +</form> +</div> +</div> +<script> +function toggle_div(nm) { +var w = document.getElementById(nm); +if( w.style.display=="block" ){ +w.style.display = "none"; +}else{ +w.style.display = "block"; +} +} +function toggle_search() { +var w = document.getElementById("searchmenu"); +if( w.style.display=="block" ){ +w.style.display = "none"; +} else { +w.style.display = "block"; +setTimeout(function(){ +document.getElementById("searchbox").focus() +}, 30); +} +} +function div_off(nm){document.getElementById(nm).style.display="none";} +window.onbeforeunload = function(e){div_off("submenu");} +/* Disable the Search feature if we are not operating from CGI, since */ +/* Search is accomplished using CGI and will not work without it. */ +if( !location.origin || !location.origin.match || !location.origin.match(/http/) ){ +document.getElementById("search_menubutton").style.display = "none"; +} +/* Used by the Hide/Show button beside syntax diagrams, to toggle the */ +function hideorshow(btn,obj){ +var x = document.getElementById(obj); +var b = document.getElementById(btn); +if( x.style.display!='none' ){ +x.style.display = 'none'; +b.innerHTML='show'; +}else{ +x.style.display = ''; +b.innerHTML='hide'; +} +return false; +} +var antiRobot = 0; +function antiRobotGo(){ +if( antiRobot!=3 ) return; +antiRobot = 7; +var j = document.getElementById("mtimelink"); +if(j && j.hasAttribute("data-href")) j.href=j.getAttribute("data-href"); +} +function antiRobotDefense(){ +document.body.onmousedown=function(){ +antiRobot |= 2; +antiRobotGo(); +document.body.onmousedown=null; +} +document.body.onmousemove=function(){ +antiRobot |= 2; +antiRobotGo(); +document.body.onmousemove=null; +} +setTimeout(function(){ +antiRobot |= 1; +antiRobotGo(); +}, 100) +antiRobotGo(); +} +antiRobotDefense(); +</script> +<!-- keywords: {busy handler} {busy-handler callback} sqlite3_busy_handler --> +<div class=nosearch> +<a href="intro.html"><h2>SQLite C Interface</h2></a> +<h2>Register A Callback To Handle SQLITE_BUSY Errors</h2> +</div> +<blockquote><pre> +int sqlite3_busy_handler(sqlite3*,int(*)(void*,int),void*); +</pre></blockquote> +<p> +The sqlite3_busy_handler(D,X,P) routine sets a callback function X +that might be invoked with argument P whenever +an attempt is made to access a database table associated with +<a href="../c3ref/sqlite3.html">database connection</a> D when another thread +or process has the table locked. +The sqlite3_busy_handler() interface is used to implement +<a href="../c3ref/busy_timeout.html">sqlite3_busy_timeout()</a> and <a href="../pragma.html#pragma_busy_timeout">PRAGMA busy_timeout</a>.</p> + +<p>If the busy callback is NULL, then <a href="../rescode.html#busy">SQLITE_BUSY</a> +is returned immediately upon encountering the lock. If the busy callback +is not NULL, then the callback might be invoked with two arguments.</p> + +<p>The first argument to the busy handler is a copy of the void* pointer which +is the third argument to sqlite3_busy_handler(). The second argument to +the busy handler callback is the number of times that the busy handler has +been invoked previously for the same locking event. If the +busy callback returns 0, then no additional attempts are made to +access the database and <a href="../rescode.html#busy">SQLITE_BUSY</a> is returned +to the application. +If the callback returns non-zero, then another attempt +is made to access the database and the cycle repeats.</p> + +<p>The presence of a busy handler does not guarantee that it will be invoked +when there is lock contention. If SQLite determines that invoking the busy +handler could result in a deadlock, it will go ahead and return <a href="../rescode.html#busy">SQLITE_BUSY</a> +to the application instead of invoking the +busy handler. +Consider a scenario where one process is holding a read lock that +it is trying to promote to a reserved lock and +a second process is holding a reserved lock that it is trying +to promote to an exclusive lock. The first process cannot proceed +because it is blocked by the second and the second process cannot +proceed because it is blocked by the first. If both processes +invoke the busy handlers, neither will make any progress. Therefore, +SQLite returns <a href="../rescode.html#busy">SQLITE_BUSY</a> for the first process, hoping that this +will induce the first process to release its read lock and allow +the second process to proceed.</p> + +<p>The default busy callback is NULL.</p> + +<p>There can only be a single busy handler defined for each +<a href="../c3ref/sqlite3.html">database connection</a>. Setting a new busy handler clears any +previously set handler. Note that calling <a href="../c3ref/busy_timeout.html">sqlite3_busy_timeout()</a> +or evaluating <a href="../pragma.html#pragma_busy_timeout">PRAGMA busy_timeout=N</a> will change the +busy handler and thus clear any previously set busy handler.</p> + +<p>The busy callback should not take any actions which modify the +database connection that invoked the busy handler. In other words, +the busy handler is not reentrant. Any such actions +result in undefined behavior.</p> + +<p>A busy handler must not close the database connection +or <a href="../c3ref/stmt.html">prepared statement</a> that invoked the busy handler. +</p><p>See also lists of + <a href="objlist.html">Objects</a>, + <a href="constlist.html">Constants</a>, and + <a href="funclist.html">Functions</a>.</p> + |