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    <title>MongoDB Jira</title>
    <link>https://jira.mongodb.org</link>
    <description>This file is an XML representation of an issue</description>
    <language>en-us</language>    <build-info>
        <version>9.7.1</version>
        <build-number>970001</build-number>
        <build-date>13-04-2023</build-date>
    </build-info>


<item>
            <title>[CDRIVER-4803] Resolve TSAN warning for multiple single-threaded clients</title>
                <link>https://jira.mongodb.org/browse/CDRIVER-4803</link>
                <project id="10030" key="CDRIVER">C Driver</project>
                    <description>&lt;h1&gt;&lt;a name=&quot;Summary&quot;&gt;&lt;/a&gt;Summary&lt;/h1&gt;

&lt;p&gt;Resolve an observed TSAN warning when using multiple single-threaded clients in separate threads. Here is an example stack trace when used in the C++ driver:&lt;/p&gt;
&lt;p/&gt;
&lt;div id=&quot;syntaxplugin&quot; class=&quot;syntaxplugin&quot; style=&quot;border: 1px dashed #bbb; border-radius: 5px !important; overflow: auto; max-height: 30em;&quot;&gt;
&lt;table cellspacing=&quot;0&quot; cellpadding=&quot;0&quot; border=&quot;0&quot; width=&quot;100%&quot; style=&quot;font-size: 1em; line-height: 1.4em !important; font-weight: normal; font-style: normal; color: black;&quot;&gt;
		&lt;tbody &gt;
				&lt;tr id=&quot;syntaxplugin_code_and_gutter&quot;&gt;
						&lt;td  style=&quot; line-height: 1.4em !important; padding: 0em; vertical-align: top;&quot;&gt;
					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;  margin-top: 10px;   width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;[j1:prim]   Previous write of size 1 at 0x7fea109b7118 by thread T105 (mutexes: write M872989262969134504):&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&gt;
				&lt;tr id=&quot;syntaxplugin_code_and_gutter&quot;&gt;
						&lt;td  style=&quot; line-height: 1.4em !important; padding: 0em; vertical-align: top;&quot;&gt;
					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;   width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;[j1:prim]     #0 _mongoc_handshake_freeze /data/mci/c5a40dbcaac77d38feef2562ae860e96/src/src/mongo/db/modules/enterprise/src/streams/third_party/mongocxx/dist/mongoc/mongoc-handshake.c:569:37 (libmongoc.so+0x88398)&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&gt;
				&lt;tr id=&quot;syntaxplugin_code_and_gutter&quot;&gt;
						&lt;td  style=&quot; line-height: 1.4em !important; padding: 0em; vertical-align: top;&quot;&gt;
					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;   width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;[j1:prim]     #1 _mongoc_topology_do_blocking_scan /data/mci/c5a40dbcaac77d38feef2562ae860e96/src/src/mongo/db/modules/enterprise/src/streams/third_party/mongocxx/dist/mongoc/mongoc-topology.c:929:4 (libmongoc.so+0xb8591)&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&gt;
				&lt;tr id=&quot;syntaxplugin_code_and_gutter&quot;&gt;
						&lt;td  style=&quot; line-height: 1.4em !important; padding: 0em; vertical-align: top;&quot;&gt;
					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;   width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;[j1:prim]     #2 mongoc_topology_select_server_id /data/mci/c5a40dbcaac77d38feef2562ae860e96/src/src/mongo/db/modules/enterprise/src/streams/third_party/mongocxx/dist/mongoc/mongoc-topology.c:1234:13 (libmongoc.so+0xb8e93)&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&gt;
				&lt;tr id=&quot;syntaxplugin_code_and_gutter&quot;&gt;
						&lt;td  style=&quot; line-height: 1.4em !important; padding: 0em; vertical-align: top;&quot;&gt;
					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;   width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;[j1:prim]     #3 _mongoc_client_end_sessions /data/mci/c5a40dbcaac77d38feef2562ae860e96/src/src/mongo/db/modules/enterprise/src/streams/third_party/mongocxx/dist/mongoc/mongoc-client.c:3034:19 (libmongoc.so+0x5a278)&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&gt;
				&lt;tr id=&quot;syntaxplugin_code_and_gutter&quot;&gt;
						&lt;td  style=&quot; line-height: 1.4em !important; padding: 0em; vertical-align: top;&quot;&gt;
					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;   width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;[j1:prim]     #4 mongoc_client_destroy /data/mci/c5a40dbcaac77d38feef2562ae860e96/src/src/mongo/db/modules/enterprise/src/streams/third_party/mongocxx/dist/mongoc/mongoc-client.c:1205:10 (libmongoc.so+0x5a082)&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&gt;
				&lt;tr id=&quot;syntaxplugin_code_and_gutter&quot;&gt;
						&lt;td  style=&quot; line-height: 1.4em !important; padding: 0em; vertical-align: top;&quot;&gt;
					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;   width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;[j1:prim]     #5 mongocxx::v_noabi::client::impl::~impl() /data/mci/c5a40dbcaac77d38feef2562ae860e96/src/src/mongo/db/modules/enterprise/src/streams/third_party/mongocxx/dist/mongocxx/private/client.hh:33:9 (libmongocxx.so+0x6d349)&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&gt;
				&lt;tr id=&quot;syntaxplugin_code_and_gutter&quot;&gt;
						&lt;td  style=&quot; line-height: 1.4em !important; padding: 0em; vertical-align: top;&quot;&gt;
					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;   width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;[j1:prim]     #6 std::default_delete&amp;lt;mongocxx::v_noabi::client::impl&amp;gt;::operator()(mongocxx::v_noabi::client::impl*) const /opt/mongodbtoolchain/revisions/69f4f0673ffcb290ce2307560a4883ecf2ad138c/stow/gcc-v4.35T/lib/gcc/x86_64-mongodb-linux/11.3.0/../../../../include/c++/11.3.0/bits/unique_ptr.h:85:2 (libmongocxx.so+0x69e7a)&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&gt;
				&lt;tr id=&quot;syntaxplugin_code_and_gutter&quot;&gt;
						&lt;td  style=&quot; line-height: 1.4em !important; padding: 0em; vertical-align: top;&quot;&gt;
					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;   width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;[j1:prim]     #7 std::unique_ptr&amp;lt;mongocxx::v_noabi::client::impl, std::default_delete&amp;lt;mongocxx::v_noabi::client::impl&amp;gt; &amp;gt;::~unique_ptr() /opt/mongodbtoolchain/revisions/69f4f0673ffcb290ce2307560a4883ecf2ad138c/stow/gcc-v4.35T/lib/gcc/x86_64-mongodb-linux/11.3.0/../../../../include/c++/11.3.0/bits/unique_ptr.h:361:4 (libmongocxx.so+0x69e7a)&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&gt;
				&lt;tr id=&quot;syntaxplugin_code_and_gutter&quot;&gt;
						&lt;td  style=&quot; line-height: 1.4em !important; padding: 0em; vertical-align: top;&quot;&gt;
					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;   width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;[j1:prim]     #8 mongocxx::v_noabi::client::~client() /data/mci/c5a40dbcaac77d38feef2562ae860e96/src/src/mongo/db/modules/enterprise/src/streams/third_party/mongocxx/dist/mongocxx/client.cpp:142:17 (libmongocxx.so+0x69e7a)&lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&gt;
				&lt;tr id=&quot;syntaxplugin_code_and_gutter&quot;&gt;
						&lt;td  style=&quot; line-height: 1.4em !important; padding: 0em; vertical-align: top;&quot;&gt;
					&lt;pre style=&quot;font-size: 1em; margin: 0 10px;   margin-bottom: 10px;  width: auto; padding: 0;&quot;&gt;&lt;span style=&quot;color: black; font-family: &apos;Consolas&apos;, &apos;Bitstream Vera Sans Mono&apos;, &apos;Courier New&apos;, Courier, monospace !important;&quot;&gt;[j1:prim]     #9 std::default_delete&amp;lt;mongocxx::v_noabi::client&amp;gt;::operator()(mongocxx::v_noabi::client*) const &lt;/span&gt;&lt;/pre&gt;
			&lt;/td&gt;
		&lt;/tr&gt;
			&lt;/tbody&gt;
&lt;/table&gt;
&lt;/div&gt;
&lt;p/&gt;
&lt;p&gt;This may require locking &lt;tt&gt;gHandshakeLock&lt;/tt&gt; around calls to &lt;tt&gt;_mongoc_handshake_freeze&lt;/tt&gt; for single-threaded clients.&lt;/p&gt;

&lt;p&gt;The TSAN warning is currently suppressed in the C driver: &lt;a href=&quot;https://github.com/mongodb/mongo-c-driver/blob/3f2c35d97e7f12de5da4f049dce4c3f8494aba67/.tsan-suppressions#L2&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/mongo-c-driver/blob/3f2c35d97e7f12de5da4f049dce4c3f8494aba67/.tsan-suppressions#L2&lt;/a&gt;&lt;/p&gt;
&lt;h1&gt;&lt;a name=&quot;Background%26Motivation&quot;&gt;&lt;/a&gt;Background &amp;amp; Motivation&lt;/h1&gt;

&lt;p&gt;I expect the warning is harmless. The TSAN warning is flagging the fact that a global is being overwritten to the same value by two different threads.&lt;/p&gt;

&lt;p&gt;Using a &lt;tt&gt;mongoc_client_pool_t&lt;/tt&gt; to obtain clients in a multi-threaded application is preferred. This may not be a commonly encountered issue. However, this was observed by an internal team and may serve as a point of confusion.&lt;/p&gt;</description>
                <environment></environment>
        <key id="2535015">CDRIVER-4803</key>
            <summary>Resolve TSAN warning for multiple single-threaded clients</summary>
                <type id="4" iconUrl="https://jira.mongodb.org/secure/viewavatar?size=xsmall&amp;avatarId=14710&amp;avatarType=issuetype">Improvement</type>
                                            <priority id="4" iconUrl="https://jira.mongodb.org/images/icons/priorities/minor.svg">Minor - P4</priority>
                        <status id="10038" iconUrl="https://jira.mongodb.org/images/icons/subtask.gif" description="">Backlog</status>
                    <statusCategory id="2" key="new" colorName="default"/>
                                    <resolution id="-1">Unresolved</resolution>
                                        <assignee username="-1">Unassigned</assignee>
                                    <reporter username="kevin.albertson@mongodb.com">Kevin Albertson</reporter>
                        <labels>
                            <label>neweng</label>
                    </labels>
                <created>Tue, 2 Jan 2024 13:30:07 +0000</created>
                <updated>Mon, 8 Jan 2024 20:19:55 +0000</updated>
                                                                                                <votes>0</votes>
                                    <watches>2</watches>
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