Adding upstream version 3.45.1.upstream/3.45.1

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
author: Daniel Baumann <daniel.baumann@progress-linux.org> 2024-04-13 14:07:11 +0000
committer: Daniel Baumann <daniel.baumann@progress-linux.org> 2024-04-13 14:07:11 +0000
commit: 63847496f14c813a5d80efd5b7de0f1294ffe1e3 (patch)
tree: 01c7571c7c762ceee70638549a99834fdd7c411b /www/c3ref/mutex_alloc.html
parent: Initial commit. (diff)
download: sqlite3-63847496f14c813a5d80efd5b7de0f1294ffe1e3.tar.xz
sqlite3-63847496f14c813a5d80efd5b7de0f1294ffe1e3.zip
1 files changed, 247 insertions, 0 deletions
diff --git a/www/c3ref/mutex_alloc.html b/www/c3ref/mutex_alloc.html
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+<title>Mutexes</title>
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+<!-- keywords: sqlite3_mutex_alloc sqlite3_mutex_enter sqlite3_mutex_free sqlite3_mutex_leave sqlite3_mutex_try -->
+<div class=nosearch>
+<a href="../c3ref/intro.html"><h2>SQLite C Interface</h2></a>
+<h2>Mutexes</h2>
+</div>
+<blockquote><pre>
+sqlite3_mutex *sqlite3_mutex_alloc(int);
+void sqlite3_mutex_free(sqlite3_mutex*);
+void sqlite3_mutex_enter(sqlite3_mutex*);
+int sqlite3_mutex_try(sqlite3_mutex*);
+void sqlite3_mutex_leave(sqlite3_mutex*);
+</pre></blockquote>
+<p>
+The SQLite core uses these routines for thread
+synchronization. Though they are intended for internal
+use by SQLite, code that links against SQLite is
+permitted to use any of these routines.</p>
+
+<p>The SQLite source code contains multiple implementations
+of these mutex routines.  An appropriate implementation
+is selected automatically at compile-time.  The following
+implementations are available in the SQLite core:</p>
+
+<p><ul>
+<li>   SQLITE_MUTEX_PTHREADS
+<li>   SQLITE_MUTEX_W32
+<li>   SQLITE_MUTEX_NOOP
+</ul></p>
+
+<p>The SQLITE_MUTEX_NOOP implementation is a set of routines
+that does no real locking and is appropriate for use in
+a single-threaded application.  The SQLITE_MUTEX_PTHREADS and
+SQLITE_MUTEX_W32 implementations are appropriate for use on Unix
+and Windows.</p>
+
+<p>If SQLite is compiled with the SQLITE_MUTEX_APPDEF preprocessor
+macro defined (with "-DSQLITE_MUTEX_APPDEF=1"), then no mutex
+implementation is included with the library. In this case the
+application must supply a custom mutex implementation using the
+<a href="../c3ref/c_config_covering_index_scan.html#sqliteconfigmutex">SQLITE_CONFIG_MUTEX</a> option of the sqlite3_config() function
+before calling sqlite3_initialize() or any other public sqlite3_
+function that calls sqlite3_initialize().</p>
+
+<p>The sqlite3_mutex_alloc() routine allocates a new
+mutex and returns a pointer to it. The sqlite3_mutex_alloc()
+routine returns NULL if it is unable to allocate the requested
+mutex.  The argument to sqlite3_mutex_alloc() must one of these
+integer constants:</p>
+
+<p><ul>
+<li>  SQLITE_MUTEX_FAST
+<li>  SQLITE_MUTEX_RECURSIVE
+<li>  SQLITE_MUTEX_STATIC_MAIN
+<li>  SQLITE_MUTEX_STATIC_MEM
+<li>  SQLITE_MUTEX_STATIC_OPEN
+<li>  SQLITE_MUTEX_STATIC_PRNG
+<li>  SQLITE_MUTEX_STATIC_LRU
+<li>  SQLITE_MUTEX_STATIC_PMEM
+<li>  SQLITE_MUTEX_STATIC_APP1
+<li>  SQLITE_MUTEX_STATIC_APP2
+<li>  SQLITE_MUTEX_STATIC_APP3
+<li>  SQLITE_MUTEX_STATIC_VFS1
+<li>  SQLITE_MUTEX_STATIC_VFS2
+<li>  SQLITE_MUTEX_STATIC_VFS3
+</ul></p>
+
+<p>The first two constants (SQLITE_MUTEX_FAST and SQLITE_MUTEX_RECURSIVE)
+cause sqlite3_mutex_alloc() to create
+a new mutex.  The new mutex is recursive when SQLITE_MUTEX_RECURSIVE
+is used but not necessarily so when SQLITE_MUTEX_FAST is used.
+The mutex implementation does not need to make a distinction
+between SQLITE_MUTEX_RECURSIVE and SQLITE_MUTEX_FAST if it does
+not want to.  SQLite will only request a recursive mutex in
+cases where it really needs one.  If a faster non-recursive mutex
+implementation is available on the host platform, the mutex subsystem
+might return such a mutex in response to SQLITE_MUTEX_FAST.</p>
+
+<p>The other allowed parameters to sqlite3_mutex_alloc() (anything other
+than SQLITE_MUTEX_FAST and SQLITE_MUTEX_RECURSIVE) each return
+a pointer to a static preexisting mutex.  Nine static mutexes are
+used by the current version of SQLite.  Future versions of SQLite
+may add additional static mutexes.  Static mutexes are for internal
+use by SQLite only.  Applications that use SQLite mutexes should
+use only the dynamic mutexes returned by SQLITE_MUTEX_FAST or
+SQLITE_MUTEX_RECURSIVE.</p>
+
+<p>Note that if one of the dynamic mutex parameters (SQLITE_MUTEX_FAST
+or SQLITE_MUTEX_RECURSIVE) is used then sqlite3_mutex_alloc()
+returns a different mutex on every call.  For the static
+mutex types, the same mutex is returned on every call that has
+the same type number.</p>
+
+<p>The sqlite3_mutex_free() routine deallocates a previously
+allocated dynamic mutex.  Attempting to deallocate a static
+mutex results in undefined behavior.</p>
+
+<p>The sqlite3_mutex_enter() and sqlite3_mutex_try() routines attempt
+to enter a mutex.  If another thread is already within the mutex,
+sqlite3_mutex_enter() will block and sqlite3_mutex_try() will return
+SQLITE_BUSY.  The sqlite3_mutex_try() interface returns <a href="../rescode.html#ok">SQLITE_OK</a>
+upon successful entry.  Mutexes created using
+SQLITE_MUTEX_RECURSIVE can be entered multiple times by the same thread.
+In such cases, the
+mutex must be exited an equal number of times before another thread
+can enter.  If the same thread tries to enter any mutex other
+than an SQLITE_MUTEX_RECURSIVE more than once, the behavior is undefined.</p>
+
+<p>Some systems (for example, Windows 95) do not support the operation
+implemented by sqlite3_mutex_try().  On those systems, sqlite3_mutex_try()
+will always return SQLITE_BUSY. In most cases the SQLite core only uses
+sqlite3_mutex_try() as an optimization, so this is acceptable
+behavior. The exceptions are unix builds that set the
+SQLITE_ENABLE_SETLK_TIMEOUT build option. In that case a working
+sqlite3_mutex_try() is required.</p>
+
+<p>The sqlite3_mutex_leave() routine exits a mutex that was
+previously entered by the same thread.   The behavior
+is undefined if the mutex is not currently entered by the
+calling thread or is not currently allocated.</p>
+
+<p>If the argument to sqlite3_mutex_enter(), sqlite3_mutex_try(),
+sqlite3_mutex_leave(), or sqlite3_mutex_free() is a NULL pointer,
+then any of the four routines behaves as a no-op.</p>
+
+<p>See also: <a href="../c3ref/mutex_held.html">sqlite3_mutex_held()</a> and <a href="../c3ref/mutex_held.html">sqlite3_mutex_notheld()</a>.
+</p><p>See also lists of
+  <a href="../c3ref/objlist.html">Objects</a>,
+  <a href="../c3ref/constlist.html">Constants</a>, and
+  <a href="../c3ref/funclist.html">Functions</a>.</p>
+
author	Daniel Baumann <daniel.baumann@progress-linux.org>	2024-04-13 14:07:11 +0000
committer	Daniel Baumann <daniel.baumann@progress-linux.org>	2024-04-13 14:07:11 +0000
commit	63847496f14c813a5d80efd5b7de0f1294ffe1e3 (patch)
tree	01c7571c7c762ceee70638549a99834fdd7c411b /www/c3ref/mutex_alloc.html
parent	Initial commit. (diff)
download	sqlite3-63847496f14c813a5d80efd5b7de0f1294ffe1e3.tar.xz sqlite3-63847496f14c813a5d80efd5b7de0f1294ffe1e3.zip