diff options
Diffstat (limited to 'www/threadsafe.html')
| -rw-r--r-- | www/threadsafe.html | 228 |
1 files changed, 228 insertions, 0 deletions
diff --git a/www/threadsafe.html b/www/threadsafe.html new file mode 100644 index 0000000..7aae4fe --- /dev/null +++ b/www/threadsafe.html @@ -0,0 +1,228 @@ +<!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>Using SQLite In Multi-Threaded Applications</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> +<div class=fancy> +<div class=nosearch> +<div class="fancy_title"> +Using SQLite In Multi-Threaded Applications +</div> +</div> + + + + + +<h1 id="overview"><span>1. </span>Overview</h1> + +<p>SQLite supports three different threading modes:</p> + +<ol> +<li><p><b>Single-thread</b>. +In this mode, all mutexes are disabled and SQLite is unsafe to use in +more than a single thread at once.</p></li> + +<li><p><b>Multi-thread</b>. +In this mode, SQLite can be safely used by multiple threads provided that +no single <a href="c3ref/sqlite3.html">database connection</a> nor any object derived from database connection, +such as a <a href="c3ref/stmt.html">prepared statement</a>, +is used in two or more threads at the same time. +</p></li> + +<li><p><b>Serialized</b>. +In serialized mode, API calls to affect or use any SQLite <a href="c3ref/sqlite3.html">database connection</a> +or any object derived from such a database connection +can be made safely from multiple threads. +The effect on an individual object is the same as if the API calls had all +been made in the same order from a single thread. The name "serialized" +arises from the fact that SQLite uses mutexes to serialize access to each +object.</p></li> +</ol> + +<p> +The threading mode can be selected at compile-time (when the SQLite +library is being compiled from source code) or at start-time (when the +application that intends to use SQLite is initializing) or at +run-time (when a new SQLite database connection is being created). +Generally speaking, run-time overrides start-time and start-time +overrides compile-time. Except, single-thread mode cannot be +overridden once selected. +</p> + +<p> +The default mode is serialized. +</p> + +<h1 id="compile_time_selection_of_threading_mode"><span>2. </span>Compile-time selection of threading mode</h1> + +<p> +Use the <a href="compile.html#threadsafe">SQLITE_THREADSAFE</a> compile-time parameter to select the +threading mode. If no <a href="compile.html#threadsafe">SQLITE_THREADSAFE</a> compile-time parameter is +present, then serialized mode is used. +This can be made explicit with +<a href="compile.html#threadsafe">-DSQLITE_THREADSAFE=1</a>. +With +<a href="compile.html#threadsafe">-DSQLITE_THREADSAFE=0</a> the threading mode is +single-thread. With +<a href="compile.html#threadsafe">-DSQLITE_THREADSAFE=2</a> the threading mode is +multi-thread. +</p> + +<p> +The return value of the <a href="c3ref/threadsafe.html">sqlite3_threadsafe()</a> interface is the value +of SQLITE_THREADSAFE set at compile-time. It does not reflect changes +to the threading mode made at runtime via the <a href="c3ref/config.html">sqlite3_config()</a> +interface or by flags given as the third argument to <a href="c3ref/open.html">sqlite3_open_v2()</a>. +</p> + +<p> +If single-thread mode is selected at compile-time, then critical +mutexing logic is omitted from the build and it is impossible to +enable either multi-thread or serialized modes at start-time or +run-time. +</p> + +<h1 id="start_time_selection_of_threading_mode"><span>3. </span>Start-time selection of threading mode</h1> + +<p> +Assuming that the compile-time threading mode is not single-thread, then +the threading mode can be changed during initialization using the +<a href="c3ref/config.html">sqlite3_config()</a> interface. The <a href="c3ref/c_config_covering_index_scan.html#sqliteconfigsinglethread">SQLITE_CONFIG_SINGLETHREAD</a> verb +puts SQLite into single-thread mode, the <a href="c3ref/c_config_covering_index_scan.html#sqliteconfigmultithread">SQLITE_CONFIG_MULTITHREAD</a> +verb sets multi-thread mode, and the <a href="c3ref/c_config_covering_index_scan.html#sqliteconfigserialized">SQLITE_CONFIG_SERIALIZED</a> verb +sets serialized mode. +</p> + +<h1 id="run_time_selection_of_threading_mode"><span>4. </span>Run-time selection of threading mode</h1> + +<p>If single-thread mode has not been selected at compile-time or start-time, +then individual database connections can be created as either multi-thread +or serialized. It is not possible to downgrade an individual database +connection to single-thread mode. Nor is it possible to escalate an +individual database connection if the compile-time or start-time mode +is single-thread.</p> + +<p>The threading mode for an individual database connection is determined +by flags given as the third argument to <a href="c3ref/open.html">sqlite3_open_v2()</a>. The +<a href="c3ref/c_open_autoproxy.html">SQLITE_OPEN_NOMUTEX</a> flag causes the database connection to be in the +multi-thread mode and the <a href="c3ref/c_open_autoproxy.html">SQLITE_OPEN_FULLMUTEX</a> flag causes the connection +to be in serialized mode. If neither flag is specified or if +<a href="c3ref/open.html">sqlite3_open()</a> or <a href="c3ref/open.html">sqlite3_open16()</a> are used instead of +<a href="c3ref/open.html">sqlite3_open_v2()</a>, then the default +mode determined by the compile-time and start-time settings is used. +</p> +<p align="center"><small><i>This page last modified on <a href="https://sqlite.org/docsrc/honeypot" id="mtimelink" data-href="https://sqlite.org/docsrc/finfo/pages/threadsafe.in?m=84a776bde3">2023-12-05 14:43:20</a> UTC </small></i></p> + |