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/mem_methods.html
parent: Initial commit. (diff)
download: sqlite3-63847496f14c813a5d80efd5b7de0f1294ffe1e3.tar.xz
sqlite3-63847496f14c813a5d80efd5b7de0f1294ffe1e3.zip
1 files changed, 200 insertions, 0 deletions
diff --git a/www/c3ref/mem_methods.html b/www/c3ref/mem_methods.html
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+<!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>Memory Allocation Routines</title>
+<!-- path=../ -->
+</head>
+<body>
+<div class=nosearch>
+<a href="../index.html">
+<img class="logo" src="../images/sqlite370_banner.gif" alt="SQLite" border="0">
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+<!-- keywords: sqlite3_mem_methods -->
+<div class=nosearch>
+<a href="../c3ref/intro.html"><h2>SQLite C Interface</h2></a>
+<h2>Memory Allocation Routines</h2>
+</div>
+<blockquote><pre>
+typedef struct sqlite3_mem_methods sqlite3_mem_methods;
+struct sqlite3_mem_methods {
+  void *(*xMalloc)(int);         /* Memory allocation function */
+  void (*xFree)(void*);          /* Free a prior allocation */
+  void *(*xRealloc)(void*,int);  /* Resize an allocation */
+  int (*xSize)(void*);           /* Return the size of an allocation */
+  int (*xRoundup)(int);          /* Round up request size to allocation size */
+  int (*xInit)(void*);           /* Initialize the memory allocator */
+  void (*xShutdown)(void*);      /* Deinitialize the memory allocator */
+  void *pAppData;                /* Argument to xInit() and xShutdown() */
+};
+</pre></blockquote>
+<p>
+An instance of this object defines the interface between SQLite
+and low-level memory allocation routines.</p>
+
+<p>This object is used in only one place in the SQLite interface.
+A pointer to an instance of this object is the argument to
+<a href="../c3ref/config.html">sqlite3_config()</a> when the configuration option is
+<a href="../c3ref/c_config_covering_index_scan.html#sqliteconfigmalloc">SQLITE_CONFIG_MALLOC</a> or <a href="../c3ref/c_config_covering_index_scan.html#sqliteconfiggetmalloc">SQLITE_CONFIG_GETMALLOC</a>.
+By creating an instance of this object
+and passing it to <a href="../c3ref/config.html">sqlite3_config</a>(<a href="../c3ref/c_config_covering_index_scan.html#sqliteconfigmalloc">SQLITE_CONFIG_MALLOC</a>)
+during configuration, an application can specify an alternative
+memory allocation subsystem for SQLite to use for all of its
+dynamic memory needs.</p>
+
+<p>Note that SQLite comes with several <a href="../malloc.html#altalloc">built-in memory allocators</a>
+that are perfectly adequate for the overwhelming majority of applications
+and that this object is only useful to a tiny minority of applications
+with specialized memory allocation requirements.  This object is
+also used during testing of SQLite in order to specify an alternative
+memory allocator that simulates memory out-of-memory conditions in
+order to verify that SQLite recovers gracefully from such
+conditions.</p>
+
+<p>The xMalloc, xRealloc, and xFree methods must work like the
+malloc(), realloc() and free() functions from the standard C library.
+SQLite guarantees that the second argument to
+xRealloc is always a value returned by a prior call to xRoundup.</p>
+
+<p>xSize should return the allocated size of a memory allocation
+previously obtained from xMalloc or xRealloc.  The allocated size
+is always at least as big as the requested size but may be larger.</p>
+
+<p>The xRoundup method returns what would be the allocated size of
+a memory allocation given a particular requested size.  Most memory
+allocators round up memory allocations at least to the next multiple
+of 8.  Some allocators round up to a larger multiple or to a power of 2.
+Every memory allocation request coming in through <a href="../c3ref/free.html">sqlite3_malloc()</a>
+or <a href="../c3ref/free.html">sqlite3_realloc()</a> first calls xRoundup.  If xRoundup returns 0,
+that causes the corresponding memory allocation to fail.</p>
+
+<p>The xInit method initializes the memory allocator.  For example,
+it might allocate any required mutexes or initialize internal data
+structures.  The xShutdown method is invoked (indirectly) by
+<a href="../c3ref/initialize.html">sqlite3_shutdown()</a> and should deallocate any resources acquired
+by xInit.  The pAppData pointer is used as the only parameter to
+xInit and xShutdown.</p>
+
+<p>SQLite holds the <a href="../c3ref/c_mutex_fast.html">SQLITE_MUTEX_STATIC_MAIN</a> mutex when it invokes
+the xInit method, so the xInit method need not be threadsafe.  The
+xShutdown method is only called from <a href="../c3ref/initialize.html">sqlite3_shutdown()</a> so it does
+not need to be threadsafe either.  For all other methods, SQLite
+holds the <a href="../c3ref/c_mutex_fast.html">SQLITE_MUTEX_STATIC_MEM</a> mutex as long as the
+<a href="../c3ref/c_config_covering_index_scan.html#sqliteconfigmemstatus">SQLITE_CONFIG_MEMSTATUS</a> configuration option is turned on (which
+it is by default) and so the methods are automatically serialized.
+However, if <a href="../c3ref/c_config_covering_index_scan.html#sqliteconfigmemstatus">SQLITE_CONFIG_MEMSTATUS</a> is disabled, then the other
+methods must be threadsafe or else make their own arrangements for
+serialization.</p>
+
+<p>SQLite will never invoke xInit() more than once without an intervening
+call to xShutdown().
+</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/mem_methods.html
parent	Initial commit. (diff)
download	sqlite3-63847496f14c813a5d80efd5b7de0f1294ffe1e3.tar.xz sqlite3-63847496f14c813a5d80efd5b7de0f1294ffe1e3.zip