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        <build-number>970001</build-number>
        <build-date>13-04-2023</build-date>
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<item>
            <title>[SERVER-40264] Change MigrationChunkCloner to be a shared pointer to synchronize object lifetime across threads</title>
                <link>https://jira.mongodb.org/browse/SERVER-40264</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;h2&gt;&lt;a name=&quot;Background&quot;&gt;&lt;/a&gt;Background&lt;/h2&gt;
&lt;p&gt;Recently, the CollectionShardingState (CSS) and CollectionShardingRuntime (CSR) received a new synchronization module &amp;#8211; the CollectionShardingRuntimeLock (CSRLock). The CSRLock is a ResourceLock meant to be used as a fancier std::mutex. It was built in order to protect lifetime access to pointers and internal structures placed upon the CSS/CSR. Users of the CSS/CSR&apos;s internal structures would take the CSRLock when accessing corresponding pointers. The CSRLock would stay in scope until these pointers do not need to be used any longer.&lt;/p&gt;

&lt;h2&gt;&lt;a name=&quot;Problem&quot;&gt;&lt;/a&gt;Problem&lt;/h2&gt;
&lt;p&gt;The CSRLock was built with a key assumption that is shared with std::mutex &amp;#8211; we are never to do I/O or network calls while we are inside the locking mechanism.&lt;/p&gt;

&lt;p&gt;In the &lt;tt&gt;MigrationChunkCloner&lt;/tt&gt;, a CSR sub-structure, we perform I/O operations. If we are doing this under the CSRLock, this can cause locking issues with other parts of the database system. The linked BF is an example of such an issue.&lt;/p&gt;

&lt;h2&gt;&lt;a name=&quot;Solution&quot;&gt;&lt;/a&gt;Solution&lt;/h2&gt;
&lt;p&gt;We&apos;d still like to protect the lifetime of the &lt;tt&gt;MigrationChunkCloner&lt;/tt&gt;, but do not want to perform I/O operations under the lock. Accordingly, we will change the &lt;tt&gt;MigrationChunkCloner&lt;/tt&gt; from a raw pointer to a shared pointer. This will prevent the object from going out of scope while references to the object exist. Since shared pointers are not thread safe, we will still use the CSRLock to safeguard the creation of additional references.&lt;/p&gt;</description>
                <environment></environment>
        <key id="720763">SERVER-40264</key>
            <summary>Change MigrationChunkCloner to be a shared pointer to synchronize object lifetime across threads</summary>
                <type id="3" iconUrl="https://jira.mongodb.org/secure/viewavatar?size=xsmall&amp;avatarId=14718&amp;avatarType=issuetype">Task</type>
                                            <priority id="3" iconUrl="https://jira.mongodb.org/images/icons/priorities/major.svg">Major - P3</priority>
                        <status id="6" iconUrl="https://jira.mongodb.org/images/icons/statuses/closed.png" description="The issue is considered finished, the resolution is correct. Issues which are closed can be reopened.">Closed</status>
                    <statusCategory id="3" key="done" colorName="success"/>
                                    <resolution id="13201">Fixed</resolution>
                                        <assignee username="blake.oler@mongodb.com">Blake Oler</assignee>
                                    <reporter username="blake.oler@mongodb.com">Blake Oler</reporter>
                        <labels>
                            <label>sharding-wfbf-day</label>
                    </labels>
                <created>Thu, 21 Mar 2019 20:14:20 +0000</created>
                <updated>Sun, 29 Oct 2023 22:22:45 +0000</updated>
                            <resolved>Mon, 25 Mar 2019 20:40:22 +0000</resolved>
                                    <version>4.1.9</version>
                                    <fixVersion>4.1.10</fixVersion>
                                    <component>Sharding</component>
                                        <votes>0</votes>
                                    <watches>1</watches>
                                                                                                                <comments>
                            <comment id="2191094" author="xgen-internal-githook" created="Mon, 25 Mar 2019 20:39:48 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{&apos;name&apos;: &apos;Blake Oler&apos;, &apos;username&apos;: &apos;BlakeIsBlake&apos;, &apos;email&apos;: &apos;blake.oler@mongodb.com&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-40264&quot; title=&quot;Change MigrationChunkCloner to be a shared pointer to synchronize object lifetime across threads&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-40264&quot;&gt;&lt;del&gt;SERVER-40264&lt;/del&gt;&lt;/a&gt; Change MigrationChunkCloner to be a shared pointer to synchronize object lifetime across threads&lt;br/&gt;
Branch: master&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/mongo/commit/1bcdfab7d16c899689f1f74f04c66ebb23a80ef5&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/mongo/commit/1bcdfab7d16c899689f1f74f04c66ebb23a80ef5&lt;/a&gt;&lt;/p&gt;</comment>
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