1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
|
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/xhtml;charset=UTF-8"/>
<meta http-equiv="X-UA-Compatible" content="IE=9"/>
<title>WiredTiger: Multithreading</title>
<link href="tabs.css" rel="stylesheet" type="text/css"/>
<script type="text/javascript" src="jquery.js"></script>
<script type="text/javascript" src="dynsections.js"></script>
<link href="navtree.css" rel="stylesheet" type="text/css"/>
<script type="text/javascript" src="resize.js"></script>
<script type="text/javascript" src="navtreedata.js"></script>
<script type="text/javascript" src="navtree.js"></script>
<script type="text/javascript">
$(document).ready(initResizable);
</script>
<link href="doxygen.css" rel="stylesheet" type="text/css" />
<link href="wiredtiger.css" rel="stylesheet" type="text/css"/>
</head>
<body>
<div id="top"><!-- do not remove this div, it is closed by doxygen! -->
<div id="titlearea">
<table cellspacing="0" cellpadding="0">
<tbody>
<tr style="height: 56px;">
<td id="projectlogo"><a href="http://wiredtiger.com/"><img alt="Logo" src="LogoFinal-header.png" alt="WiredTiger" /></a></td>
<td style="padding-left: 0.5em;">
<div id="projectname">
 <span id="projectnumber">Version 3.2.1</span>
</div>
<div id="projectbrief"><!-- 3.2.1 --></div>
</td>
</tr>
</tbody>
</table>
</div>
<div class="banner">
<a href="https://github.com/wiredtiger/wiredtiger">Fork me on GitHub</a>
<a class="last" href="http://groups.google.com/group/wiredtiger-users">Join my user group</a>
</div>
<!-- end header part -->
<!-- Generated by Doxygen 1.8.13 -->
<script type="text/javascript" src="menudata.js"></script>
<script type="text/javascript" src="menu.js"></script>
<script type="text/javascript">
$(function() {
initMenu('',false,false,'search.php','Search');
});
</script>
<div id="main-nav"></div>
</div><!-- top -->
<div id="side-nav" class="ui-resizable side-nav-resizable">
<div id="nav-tree">
<div id="nav-tree-contents">
<div id="nav-sync" class="sync"></div>
</div>
</div>
<div id="splitbar" style="-moz-user-select:none;"
class="ui-resizable-handle">
</div>
</div>
<script type="text/javascript">
$(document).ready(function(){initNavTree('threads.html','');});
</script>
<div id="doc-content">
<div class="header">
<div class="headertitle">
<div class="title">Multithreading </div> </div>
</div><!--header-->
<div class="contents">
<div class="textblock"><p>All <a class="el" href="struct_w_t___c_o_n_n_e_c_t_i_o_n.html" title="A connection to a WiredTiger database. ">WT_CONNECTION</a> methods are thread safe, and <a class="el" href="struct_w_t___c_o_n_n_e_c_t_i_o_n.html" title="A connection to a WiredTiger database. ">WT_CONNECTION</a> handles can be shared between threads. Applications typically open a single connection to each database, per process. Multi-threaded programs must wait for all other threads to exit before closing the <a class="el" href="struct_w_t___c_o_n_n_e_c_t_i_o_n.html" title="A connection to a WiredTiger database. ">WT_CONNECTION</a> handle because that will implicitly close all other handles. Alternatively, a thread can set an event handler using <a class="el" href="struct_w_t___c_o_n_n_e_c_t_i_o_n.html#adad5965cd4a60f65b5ac01f7ca6d1fc0" title="Open a session. ">WT_CONNECTION::open_session</a> to be notified when a <a class="el" href="struct_w_t___c_o_n_n_e_c_t_i_o_n.html" title="A connection to a WiredTiger database. ">WT_CONNECTION</a> close is in progress.</p>
<p><a class="el" href="struct_w_t___s_e_s_s_i_o_n.html" title="All data operations are performed in the context of a WT_SESSION. ">WT_SESSION</a> and <a class="el" href="struct_w_t___c_u_r_s_o_r.html" title="A WT_CURSOR handle is the interface to a cursor. ">WT_CURSOR</a> methods are not thread safe and <a class="el" href="struct_w_t___s_e_s_s_i_o_n.html" title="All data operations are performed in the context of a WT_SESSION. ">WT_SESSION</a> and <a class="el" href="struct_w_t___c_u_r_s_o_r.html" title="A WT_CURSOR handle is the interface to a cursor. ">WT_CURSOR</a> handles cannot be accessed concurrently by multiple threads. Applications typically open one <a class="el" href="struct_w_t___s_e_s_s_i_o_n.html" title="All data operations are performed in the context of a WT_SESSION. ">WT_SESSION</a> handle for each thread accessing a database, and then one or more <a class="el" href="struct_w_t___c_u_r_s_o_r.html" title="A WT_CURSOR handle is the interface to a cursor. ">WT_CURSOR</a> handles within the session.</p>
<p><a class="el" href="struct_w_t___s_e_s_s_i_o_n.html" title="All data operations are performed in the context of a WT_SESSION. ">WT_SESSION</a> and <a class="el" href="struct_w_t___c_u_r_s_o_r.html" title="A WT_CURSOR handle is the interface to a cursor. ">WT_CURSOR</a> methods may be accessed by different threads serially (for example, a pool of threads managed by the application with a set of shared session or cursor handles). There is no thread-local state in WiredTiger, and no built-in synchronization of session or cursor handles, either, so if multiple threads access a session or cursor handle, access must be serialized by the application.</p>
<p><a class="el" href="struct_w_t___a_s_y_n_c___o_p.html" title="A WT_ASYNC_OP handle is the interface to an asynchronous operation. ">WT_ASYNC_OP</a> methods are not thread-safe, and must be accessed by only a single thread at a time. <a class="el" href="struct_w_t___a_s_y_n_c___o_p.html" title="A WT_ASYNC_OP handle is the interface to an asynchronous operation. ">WT_ASYNC_OP</a> methods may be accessed by different threads serially (and that is expected to happen when the asynchronous callback function runs).</p>
<h1><a class="anchor" id="threads_example"></a>
Code samples</h1>
<p>The code below is taken from the complete example program <a class="el" href="ex_thread_8c-example.html">ex_thread.c</a>.</p>
<p>This is an example of a thread entry point. A new session is opened for the thread and used for all operations within that thread.</p>
<div class="fragment"><div class="line"><span class="keyword">static</span> WT_THREAD_RET</div><div class="line">scan_thread(<span class="keywordtype">void</span> *conn_arg)</div><div class="line">{</div><div class="line"> <a class="code" href="struct_w_t___c_o_n_n_e_c_t_i_o_n.html">WT_CONNECTION</a> *conn;</div><div class="line"> <a class="code" href="struct_w_t___c_u_r_s_o_r.html">WT_CURSOR</a> *cursor;</div><div class="line"> <a class="code" href="struct_w_t___s_e_s_s_i_o_n.html">WT_SESSION</a> *session;</div><div class="line"> <span class="keywordtype">int</span> ret;</div><div class="line"> <span class="keyword">const</span> <span class="keywordtype">char</span> *key, *value;</div><div class="line"></div><div class="line"> conn = conn_arg;</div><div class="line"> error_check(conn-><a class="code" href="struct_w_t___c_o_n_n_e_c_t_i_o_n.html#adad5965cd4a60f65b5ac01f7ca6d1fc0">open_session</a>(conn, NULL, NULL, &session));</div><div class="line"> error_check(session-><a class="code" href="struct_w_t___s_e_s_s_i_o_n.html#afb5b4a69c2c5cafe411b2b04fdc1c75d">open_cursor</a>(session, <span class="stringliteral">"table:access"</span>, NULL, NULL, &cursor));</div><div class="line"></div><div class="line"> <span class="comment">/* Show all records. */</span></div><div class="line"> <span class="keywordflow">while</span> ((ret = cursor-><a class="code" href="struct_w_t___c_u_r_s_o_r.html#a0503f16bd8f3d05aa3552f229b3a8e1b">next</a>(cursor)) == 0) {</div><div class="line"> error_check(cursor-><a class="code" href="struct_w_t___c_u_r_s_o_r.html#af19f6f9d9c7fc248ab38879032620b2f">get_key</a>(cursor, &key));</div><div class="line"> error_check(cursor-><a class="code" href="struct_w_t___c_u_r_s_o_r.html#af85364a5af50b95bbc46c82e72f75c01">get_value</a>(cursor, &value));</div><div class="line"></div><div class="line"> printf(<span class="stringliteral">"Got record: %s : %s\n"</span>, key, value);</div><div class="line"> }</div><div class="line"> <span class="keywordflow">if</span> (ret != <a class="code" href="group__wt.html#ga3c9e1b494d95cf34404ab7a974af6bf8">WT_NOTFOUND</a>)</div><div class="line"> fprintf(stderr, <span class="stringliteral">"WT_CURSOR.next: %s\n"</span>, session-><a class="code" href="struct_w_t___s_e_s_s_i_o_n.html#abe03ccb716e097ed1bb4d42eb733c1f9">strerror</a>(session, ret));</div><div class="line"></div><div class="line"> <span class="keywordflow">return</span> (WT_THREAD_RET_VALUE);</div><div class="line">}</div></div><!-- fragment --><p> Here is the main function that starts the threads. It opens a single connection, shared between the threads, and closes the connection after waiting for all of the threads to exit.</p>
<div class="fragment"><div class="line"><span class="keywordtype">int</span></div><div class="line">main(<span class="keywordtype">int</span> argc, <span class="keywordtype">char</span> *argv[])</div><div class="line">{</div><div class="line"> <a class="code" href="struct_w_t___c_o_n_n_e_c_t_i_o_n.html">WT_CONNECTION</a> *conn;</div><div class="line"> <a class="code" href="struct_w_t___s_e_s_s_i_o_n.html">WT_SESSION</a> *session;</div><div class="line"> <a class="code" href="struct_w_t___c_u_r_s_o_r.html">WT_CURSOR</a> *cursor;</div><div class="line"> wt_thread_t threads[NUM_THREADS];</div><div class="line"> <span class="keywordtype">int</span> i;</div><div class="line"></div><div class="line"> home = example_setup(argc, argv);</div><div class="line"></div><div class="line"> error_check(<a class="code" href="group__wt.html#gacbe8d118f978f5bfc8ccb4c77c9e8813">wiredtiger_open</a>(home, NULL, <span class="stringliteral">"create"</span>, &conn));</div><div class="line"></div><div class="line"> error_check(conn-><a class="code" href="struct_w_t___c_o_n_n_e_c_t_i_o_n.html#adad5965cd4a60f65b5ac01f7ca6d1fc0">open_session</a>(conn, NULL, NULL, &session));</div><div class="line"> error_check(session-><a class="code" href="struct_w_t___s_e_s_s_i_o_n.html#a358ca4141d59c345f401c58501276bbb">create</a>(session, <span class="stringliteral">"table:access"</span>, <span class="stringliteral">"key_format=S,value_format=S"</span>));</div><div class="line"> error_check(session-><a class="code" href="struct_w_t___s_e_s_s_i_o_n.html#afb5b4a69c2c5cafe411b2b04fdc1c75d">open_cursor</a>(session, <span class="stringliteral">"table:access"</span>, NULL, <span class="stringliteral">"overwrite"</span>, &cursor));</div><div class="line"> cursor-><a class="code" href="struct_w_t___c_u_r_s_o_r.html#ad1088d719df40babc1f57d086691ebdc">set_key</a>(cursor, <span class="stringliteral">"key1"</span>);</div><div class="line"> cursor-><a class="code" href="struct_w_t___c_u_r_s_o_r.html#a27f7cbd0cd3e561f6a145704813ad64c">set_value</a>(cursor, <span class="stringliteral">"value1"</span>);</div><div class="line"> error_check(cursor-><a class="code" href="struct_w_t___c_u_r_s_o_r.html#aac90d9fbcc031570f924db55f8a1cee3">insert</a>(cursor));</div><div class="line"> error_check(session-><a class="code" href="struct_w_t___s_e_s_s_i_o_n.html#a96f25dfa6447034aea1f67ab02ab5698">close</a>(session, NULL));</div><div class="line"></div><div class="line"> <span class="keywordflow">for</span> (i = 0; i < NUM_THREADS; i++)</div><div class="line"> error_check(__wt_thread_create(NULL, &threads[i], scan_thread, conn));</div><div class="line"></div><div class="line"> <span class="keywordflow">for</span> (i = 0; i < NUM_THREADS; i++)</div><div class="line"> error_check(__wt_thread_join(NULL, &threads[i]));</div><div class="line"></div><div class="line"> error_check(conn-><a class="code" href="struct_w_t___c_o_n_n_e_c_t_i_o_n.html#af535c517df851eeac8ebf3594d40b545">close</a>(conn, NULL));</div><div class="line"></div><div class="line"> <span class="keywordflow">return</span> (EXIT_SUCCESS);</div><div class="line">}</div></div><!-- fragment --></div></div><!-- contents -->
</div><!-- doc-content -->
<!-- start footer part -->
<div id="nav-path" class="navpath"><!-- id is needed for treeview function! -->
<ul>
<li class="navelem"><a class="el" href="index.html">Reference Guide</a></li><li class="navelem"><a class="el" href="programming.html">Writing WiredTiger applications</a></li>
<li class="footer">Copyright (c) 2008-2019 MongoDB, Inc. All rights reserved. Contact <a href="mailto:info@wiredtiger.com">info@wiredtiger.com</a> for more information.</li>
</ul>
</div>
</body>
</html>
|
