Re: Tomcat 10 and virtual thread

Francois,

On 11/4/25 4:50 AM, COURTAULT Francois wrote:
> THALES GROUP LIMITED DISTRIBUTION to email recipients
> 
> Hello Christopher,
> 
> Just to be sure ...
> 
> For HTTP/1.1 request traffic and virtual thread usage, your recommendation is:
>     - Executor declaration in server.xml like:
>        <Executor name="virtualThread"
>                                        className="org.apache.catalina.core.StandardVirtualThreadExecutor" />
>     -  Connector declaration in server.xml like:
>        <Connector executor="virtualThread" port="8080" protocol="org.apache.coyote.http11.Http11NioProtocol"
>                   connectionTimeout="20000"
>                   redirectPort="8443"
>                   maxParameterCount="1000">
>        </Connector>
> 
> instead of this connector only declaration like:
>        <Connector port="8080" protocol="org.apache.coyote.http11.Http11NioProtocol"
>                   connectionTimeout="20000"
>                   redirectPort="8443"
>                   maxParameterCount="1000"
>                   useVirtualThreads="true">              ==> create a executor where the className is set to org.apache.catalina.core.StandardVirtualThreadExecutor
>        </Connector>
> or like:
>     <Connector port="8080" protocol="HTTP/1.1"
>                   connectionTimeout="20000"
>                   redirectPort="8443"
>                   maxParameterCount="1000"
>                   useVirtualThreads="true" />            ==> create a executor where the className is set to org.apache.catalina.core.StandardVirtualThreadExecutor
> 
> Is my understanding of your recommendation correct ?

Yes, that is my recommendation, based upon the increased flexibility of 
configuration you get from separate <Executor> and <Connector>.

If you don't need a complicated configuration, it may be "simpler" 
and/or "easier to read" if you have only a single <Connector> with 
useVirtualThreads="true". So it's really your choice.

In either case -- have you been successful in getting virtual threads to 
work?

-chris

> -----Original Message-----
> From: Christopher Schultz <[email protected]>
> Sent: lundi 3 novembre 2025 20:08
> To: [email protected]
> Subject: Re: Tomcat 10 and virtual thread
> 
> Francois,
> 
> On 11/3/25 1:39 PM, COURTAULT Francois wrote:
>> I am confused because the way (see underneath) I configured initially seems OK: it triggers the virtual thread usage. Indeed I am able to see ForkJoinPool-1-worker-1  😊 in the thread dump I triggered
>>      *   first, declare an executor in server.xml like below
>>                    <Executor name="virtualThread"
>>                                       className="org.apache.catalina.core.StandardVirtualThreadExecutor" />
>>     *   second, use a connector which will refer this above Executor thanks to its name attribute.
>>          The way I do it, is to update line 74, in server.xml, from <Connector port="8080" protocol="HTTP/1.1" to
>>                                                                                                            <Connector executor="virtualThread" port="8080" protocol="HTTP/1.1"
>>
>> If now I look at
>> https://tomcat.apache.org/tomcat-10.1-doc/config/http.html
>> The useVirtualThreads attribute is listed under the Standard Implementation section which talks about standard HTTP connectors (NIO and NIO2).
>> So we should only use for protocol attribute one of the following Http11NioProtocol and Http11Nio2Protocol protocols.
>>
>> In your configuration, you don't use one of these above protocols.
>>
>> Why having several ways to enable virtual threads usage ?
> 
> This is historical. Tomcat used to support only <Connector> and then <Executor> was introduced, later. In order to support backward-compatible (and simpler) configurations, <Connector> will create an <Executor> if the <Connector> does not specify an <Executor>.
> 
>> So, what is the recommended configuration, for using virtual thread, to use ?
>>      - Define a new Executor with StandardVirtualThreadExecutor  as a className attribute
>>        Define a connector on HTTP protocol with an executor attribute set to the name of the new Executor
>>      - Or
>>           <Connector port="8080" protocol="org.apache.coyote.http11.Http11NioProtocol" or "org.apache.coyote.http11.Http11Nio2Protocol"
>>                  connectionTimeout="20000"
>>                  redirectPort="8443"
>>                  maxParameterCount="1000"
>>                  useVirtualThreads="true">
>>           </Connector>
>>
>> BTW for HTTP1.0/1.1 traffic with no TLS what Connector should we use ?
>>        -   <Connector port="8080" protocol="HTTP/1.1"
>>       - or <Connector port="8080" protocol=" org.apache.coyote.http11.Http11NioProtocol"
>>       - or <Connector port="8080" protocol=" org.apache.coyote.http11.Http11Nio2Protocol"
> 
> I would recommend <Connector> + <Executor> because <Executor> supports more configuration options for the executor itself than <Connector> does. For example, configuring an <Executor> explicitly allows you to have a thread-pool whose connections can be retired after inactivity.
> 
> (That doesn't matter at all for Virtual Threads, as the thread pool itself is essentially always empty -- no threads are ever re-used.)
> 
> If you are looking for unrelated recommendations, I would also use NIO instead of NIO2. NIO has far more usage in the real world than NIO2.
> NIO2 uses a different I/O model which was supposed to be much faster than NIO, but then NIO improved significantly and the promises of NIO2 were realized by NIO. *shrug*
> 
> -chris
> 
>> -----Original Message-----
>> From: William Crowell <[email protected]>
>> Sent: lundi 3 novembre 2025 17:15
>> To: Tomcat Users List <[email protected]>
>> Subject: Re: Tomcat 10 and virtual thread
>>
>> Hi,
>>
>> I have never tried doing it through the executor like that.  How I enable virtual threads in server.xml is like this:
>>
>>    <Connector port="8080" protocol="HTTP/1.1"
>>                  connectionTimeout="20000"
>>                  redirectPort="8443"
>>                  maxParameterCount="1000"
>>                  useVirtualThreads="true" />
>>
>> You should be using at least JDK21 for that to work.  When you do a thread dump you will see virtual threads in the dump.
>>
>> Extra info FYI: Running with JVM argument -Djdk.tracePinnedThreads=full prints a complete stack trace when a thread blocks while pinned, with the native frames and frames holding monitors highlighted. Running with -Djdk.tracePinnedThreads=short limits the output to just the problematic frames:
>>
>> Thread[#41,ForkJoinPool-1-worker-4,5,CarrierThreads]
>>       com.mysql.cj.jdbc.ConnectionImpl.isValid(ConnectionImpl.java:2516) <== monitors:1 Thread[#39,ForkJoinPool-1-worker-2,5,CarrierThreads]
>>       com.mysql.cj.jdbc.ConnectionImpl.isValid(ConnectionImpl.java:2516) <== monitors:1 Thread[#41,ForkJoinPool-1-worker-4,5,CarrierThreads]
>>       com.mysql.cj.jdbc.ConnectionImpl.setAutoCommit(ConnectionImpl.java:2005) <== monitors:1 Thread[#43,ForkJoinPool-1-worker-5,5,CarrierThreads]
>>       com.mysql.cj.jdbc.ClientPreparedStatement.executeInternal(ClientPreparedStatement.java:893) <== monitors:1
>>       com.mysql.cj.jdbc.ClientPreparedStatement.executeUpdateInternal(ClientPreparedStatement.java:1061) <== monitors:1
>>       com.mysql.cj.jdbc.ClientPreparedStatement.executeUpdateInternal(ClientPreparedStatement.java:1009) <== monitors:1 Thread[#43,ForkJoinPool-1-worker-5,5,CarrierThreads]
>>       com.mysql.cj.jdbc.ConnectionImpl.commit(ConnectionImpl.java:791) <== monitors:1 Thread[#43,ForkJoinPool-1-worker-5,5,CarrierThreads]
>>
>> com.mysql.cj.jdbc.ConnectionImpl.setAutoCommit(ConnectionImpl.java:200
>> 5) <== monitors:1
>>
>> Regards,
>>
>> William Crowell
>>
>> From: COURTAULT Francois <[email protected]>
>> Date: Monday, November 3, 2025 at 11:05 AM
>> To: [email protected] <[email protected]>
>> Subject: Tomcat 10 and virtual thread
>>
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>> THALES GROUP LIMITED DISTRIBUTION to email recipients
>>
>> Hello everyone,
>>
>> Looking at https://tomcat.apache.org/tomcat-10.1-doc/config/executor.html we can configure Tomcat 10.1.x to use virtual threads instead of platform threads. Do you confirm ?
>>
>> The way to do it, as far as I understood, is to:
>>
>>     *   first, declare an executor in server.xml like below
>> <Executor name="virtualThread"
>>
>> className="org.apache.catalina.core.StandardVirtualThreadExecutor" />
>>
>>     *   second, use a connector which will refer this above Executor thanks to its name attribute.
>> The way I do it, is to update line 74, in server.xml, from <Connector port="8080" protocol="HTTP/1.1" to
>>                                                                                                                            <Connector executor="virtualThread" port="8080" protocol="HTTP/1.1"
>>
>> I started Tomcat and triggered a thread dump.
>> I was not able to see any tomcat-virt string.
>> Does it mean that the virtual thread usage is still disabled ?
>>
>> What's wrong with my configuration ?
>>
>> Best Regards.
>>
>>
>>
>>
>>
>>
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