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authorDaniel Baumann <daniel.baumann@progress-linux.org>2024-05-05 17:28:19 +0000
committerDaniel Baumann <daniel.baumann@progress-linux.org>2024-05-05 17:28:19 +0000
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parentInitial commit. (diff)
downloadsqlite3-18657a960e125336f704ea058e25c27bd3900dcb.tar.xz
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Adding upstream version 3.40.1.upstream/3.40.1upstream
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
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+<!-- keywords: sqlite3_mutex_methods -->
+<div class=nosearch>
+<a href="intro.html"><h2>SQLite C Interface</h2></a>
+<h2>Mutex Methods Object</h2>
+</div>
+<blockquote><pre>
+typedef struct sqlite3_mutex_methods sqlite3_mutex_methods;
+struct sqlite3_mutex_methods {
+ int (*xMutexInit)(void);
+ int (*xMutexEnd)(void);
+ sqlite3_mutex *(*xMutexAlloc)(int);
+ void (*xMutexFree)(sqlite3_mutex *);
+ void (*xMutexEnter)(sqlite3_mutex *);
+ int (*xMutexTry)(sqlite3_mutex *);
+ void (*xMutexLeave)(sqlite3_mutex *);
+ int (*xMutexHeld)(sqlite3_mutex *);
+ int (*xMutexNotheld)(sqlite3_mutex *);
+};
+</pre></blockquote>
+<p>
+An instance of this structure defines the low-level routines
+used to allocate and use mutexes.</p>
+
+<p>Usually, the default mutex implementations provided by SQLite are
+sufficient, however the application has the option of substituting a custom
+implementation for specialized deployments or systems for which SQLite
+does not provide a suitable implementation. In this case, the application
+creates and populates an instance of this structure to pass
+to sqlite3_config() along with the <a href="../c3ref/c_config_covering_index_scan.html#sqliteconfigmutex">SQLITE_CONFIG_MUTEX</a> option.
+Additionally, an instance of this structure can be used as an
+output variable when querying the system for the current mutex
+implementation, using the <a href="../c3ref/c_config_covering_index_scan.html#sqliteconfiggetmutex">SQLITE_CONFIG_GETMUTEX</a> option.</p>
+
+<p>The xMutexInit method defined by this structure is invoked as
+part of system initialization by the sqlite3_initialize() function.
+The xMutexInit routine is called by SQLite exactly once for each
+effective call to <a href="../c3ref/initialize.html">sqlite3_initialize()</a>.</p>
+
+<p>The xMutexEnd method defined by this structure is invoked as
+part of system shutdown by the sqlite3_shutdown() function. The
+implementation of this method is expected to release all outstanding
+resources obtained by the mutex methods implementation, especially
+those obtained by the xMutexInit method. The xMutexEnd()
+interface is invoked exactly once for each call to <a href="../c3ref/initialize.html">sqlite3_shutdown()</a>.</p>
+
+<p>The remaining seven methods defined by this structure (xMutexAlloc,
+xMutexFree, xMutexEnter, xMutexTry, xMutexLeave, xMutexHeld and
+xMutexNotheld) implement the following interfaces (respectively):</p>
+
+<p><ul>
+<li> <a href="../c3ref/mutex_alloc.html">sqlite3_mutex_alloc()</a> </li>
+<li> <a href="../c3ref/mutex_alloc.html">sqlite3_mutex_free()</a> </li>
+<li> <a href="../c3ref/mutex_alloc.html">sqlite3_mutex_enter()</a> </li>
+<li> <a href="../c3ref/mutex_alloc.html">sqlite3_mutex_try()</a> </li>
+<li> <a href="../c3ref/mutex_alloc.html">sqlite3_mutex_leave()</a> </li>
+<li> <a href="../c3ref/mutex_held.html">sqlite3_mutex_held()</a> </li>
+<li> <a href="../c3ref/mutex_held.html">sqlite3_mutex_notheld()</a> </li>
+</ul></p>
+
+<p>The only difference is that the public sqlite3_XXX functions enumerated
+above silently ignore any invocations that pass a NULL pointer instead
+of a valid mutex handle. The implementations of the methods defined
+by this structure are not required to handle this case. The results
+of passing a NULL pointer instead of a valid mutex handle are undefined
+(i.e. it is acceptable to provide an implementation that segfaults if
+it is passed a NULL pointer).</p>
+
+<p>The xMutexInit() method must be threadsafe. It must be harmless to
+invoke xMutexInit() multiple times within the same process and without
+intervening calls to xMutexEnd(). Second and subsequent calls to
+xMutexInit() must be no-ops.</p>
+
+<p>xMutexInit() must not use SQLite memory allocation (<a href="../c3ref/free.html">sqlite3_malloc()</a>
+and its associates). Similarly, xMutexAlloc() must not use SQLite memory
+allocation for a static mutex. However xMutexAlloc() may use SQLite
+memory allocation for a fast or recursive mutex.</p>
+
+<p>SQLite will invoke the xMutexEnd() method when <a href="../c3ref/initialize.html">sqlite3_shutdown()</a> is
+called, but only if the prior call to xMutexInit returned SQLITE_OK.
+If xMutexInit fails in any way, it is expected to clean up after itself
+prior to returning.
+</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>
+
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