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:2005) <== 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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> 
> 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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