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    <div class="moz-cite-prefix">On 05/07/2025 21:25, Ryan Yeats wrote:<br>

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    <blockquote type="cite" cite="mid:CAO4jUyUObxU=NuMLabfEHt2MSBiWzjWEfncg0YKQNsukoKUgjg@mail.gmail.com">

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              <li>Its not easy to replace the virtual thread scheduler</li>

              <li>The aforementioned scheduler has no understanding of

                delays so any Thread.sleep or Object.wait introduces

                continuations back into the scheduled execution pool

                non-deterministically. This affects the execution order

                so bugs can't always be reproduced.</li>

              <li>IO also introduces continuations back to the scheduler

                execution pool non-deterministically.</li>

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            <div>The first issue can currently be solved by using

              reflection to make the <a href="https://github.com/ryeats/loom-dst/blob/main/src/main/java/org/example/SchedulableVirtualThreadFactory.java" moz-do-not-send="true">virtual thread constructor public</a>. The

              second issue can currently be solved by controlling system

              time by replacing the byte code for all calls to

              System.nanoTime(), System.onCurrentTimeMillis() and

              Instant.now() <a href="https://github.com/cmu-pasta/fray/blob/main/instrumentation/base/src/main/kotlin/org/pastalab/fray/instrumentation/base/visitors/TimeInstrumenter.kt" moz-do-not-send="true">using an agent at runtime</a>.

              The third likely has no general solution but I am

              interested in hearing ideas.</div>

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    There are experimental changes in the loom repo to allow the virtual

    thread scheduler be replaced or wrapped. There is also a prototype

    API to set a scheduler when creating a virtual Thread. There is a

    doc in the repo with more on this [1]. This project hasn't decided

    whether to expose anything so any reports from experiments would be

    useful to hear about.<br>

    <br>

    -Alan<br>

    <br>

    [1]

<a class="moz-txt-link-freetext" href="https://github.com/openjdk/loom/blob/fibers/loom-docs/CustomSchedulers.md">https://github.com/openjdk/loom/blob/fibers/loom-docs/CustomSchedulers.md</a><br>

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