<!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. 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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 database connection is used simultaneously in two or more threads. </p></li> <li><p><b>Serialized</b>. In serialized mode, SQLite can be safely used by multiple threads with no restriction.</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=fc623895ed39582cf">2022-01-20 21:38:08</a> UTC </small></i></p>