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Hi,</div>
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A reproducer which requires breakpoints and debuggers will not be practical to try to fashion a regression test after, unfortunately.<br>
If you're able to create a reproducer (even if it requires many iterations), please share.</div>
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Cheers,<br>
√</div>
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<br>
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<b><br>
</b></div>
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<b>Viktor Klang</b></div>
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Software Architect, Java Platform Group<br>
Oracle</div>
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Confidential – Oracle Internal</div>
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<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" style="font-size:11pt" color="#000000"><b>From:</b> 徐佳 <75317544@qq.com><br>
<b>Sent:</b> Thursday, 23 October 2025 14:52<br>
<b>To:</b> Viktor Klang <viktor.klang@oracle.com>; Joe Darcy <joe.darcy@oracle.com>; core-libs-dev <core-libs-dev@openjdk.org><br>
<b>Subject:</b> [External] : Re: ForkJoinPool of JDK21 : Despite having an idle worker, thesubmitted task did not run</font>
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thanks for your response.</div>
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did you run the code by debug？ </div>
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The probability of this happening is very small，We need to use debug to reproduce it , and step by step as I mentioned in my previous email.</div>
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After careful consideration, I no longer believe that this is a bug. The author should have designed it this way, as the probability of this happening is very small and recoverable。</div>
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<pre style="margin:0px"><div style="text-align:left; text-indent:0px; white-space:normal; font-size:13px; color:rgb(19,24,29)"><span style="line-height:1.5"><br></span></div></pre>
<pre style="margin:0px"><div style="text-align:left; text-indent:0px; font-size:13px; color:rgb(19,24,29)"><span style="line-height:1.5"><code>Thanks,</code></span></div></pre>
<pre style="margin:0px"><div style="text-align:left; text-indent:0px; font-size:13px; color:rgb(19,24,29)"><span style="line-height:1.5"><code>Jia Xu</code></span></div></pre>
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<div style="line-height:20px; font-size:12px"><span style="color:rgb(92,97,102)">发件人：</span><span style="color:rgb(0,0,0)">Viktor Klang</span>
<span style="color:rgb(149,157,166)"><viktor.klang@oracle.com></span></div>
<div style="line-height:20px; font-size:12px"><span style="color:rgb(92,97,102)">发件时间：</span><span style="color:rgb(0,0,0)">2025年10月23日 18:27</span></div>
<div style="line-height:20px; font-size:12px"><span style="color:rgb(92,97,102)">收件人：</span><span style="color:rgb(0,0,0)">Joe Darcy</span>
<span style="color:rgb(149,157,166)"><joe.darcy@oracle.com>, </span><span style="color:rgb(0,0,0)">徐佳</span>
<span style="color:rgb(149,157,166)"><75317544@qq.com>, </span><span style="color:rgb(0,0,0)">core-libs-dev</span>
<span style="color:rgb(149,157,166)"><core-libs-dev@openjdk.org></span></div>
<div style="line-height:20px; font-size:12px"><span style="color:rgb(92,97,102)">主题：</span><span style="color:rgb(0,0,0)">Re: ForkJoinPool of JDK21 : Despite having an idle worker, thesubmitted task did not run</span></div>
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Also, this doesn't reproduce for me.<br>
<br>
<b>/Library/Java/JavaVirtualMachines/jdk-21.jdk/Contents/Home/bin/java -version</b></div>
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java version "21.0.8" 2025-07-15 LTS</div>
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Java(TM) SE Runtime Environment (build 21.0.8+12-LTS-250)</div>
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Java HotSpot(TM) 64-Bit Server VM (build 21.0.8+12-LTS-250, mixed mode, sharing)</div>
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<b>/Library/Java/JavaVirtualMachines/jdk-21.jdk/Contents/Home/bin/java ~/Desktop/ForkJoinPoolTest.java </b></div>
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===================</div>
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submited task1</div>
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QueuedSubmissionCount:1</div>
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ActiveThreadCount:2</div>
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PoolSize:2</div>
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===================</div>
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ForkJoinPool-1-worker-2 : finished task1</div>
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submited task2</div>
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ForkJoinPool-1-worker-2 : finished task2</div>
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===================</div>
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QueuedSubmissionCount:0</div>
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ActiveThreadCount:1</div>
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PoolSize:2</div>
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===================</div>
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===================</div>
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QueuedSubmissionCount:0</div>
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ActiveThreadCount:1</div>
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PoolSize:2</div>
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===================</div>
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^C% </div>
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Cheers,<br>
√</div>
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<div style="font-family:Calibri,Arial,Helvetica,sans-serif; font-size:12pt; color:rgb(0,0,0)">
<b>Viktor Klang</b></div>
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Software Architect, Java Platform Group<br>
Oracle</div>
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<div style="direction:ltr"><span style="font-family:Calibri,sans-serif; font-size:11pt; color:rgb(0,0,0)"><b>From:</b> core-libs-dev <core-libs-dev-retn@openjdk.org> on behalf of Joseph D. Darcy <joe.darcy@oracle.com><br>
<b>Sent:</b> Thursday, 23 October 2025 01:02<br>
<b>To:</b> 徐佳 <75317544@qq.com>; core-libs-dev <core-libs-dev@openjdk.org><br>
<b>Subject:</b> Re: ForkJoinPool of JDK21 : Despite having an idle worker, the submitted task did not run</span>
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<div>Jia Xu, this mailing list is not a forum to submit bugs.<br>
<br>
>From <a href="https://openjdk.org/guide/#jbs---jdk-bug-system" class="x_x_moz-txt-link-freetext" style="text-decoration:underline">
https://openjdk.org/guide/#jbs---jdk-bug-system</a>, if you don't have a JBS account, you can submit bugs at
<a href="https://urldefense.com/v3/__https://bugreport.java.com/bugreport/__;!!ACWV5N9M2RV99hQ!Pu1K5WZbNoapUo15ono9LryUKTm-QxtiLinbI9XSEnlfm3nQNo6Ryv-VYHFClMbO6AbQ7qCEvHkEfjijTA$" class="x_x_moz-txt-link-freetext" style="text-decoration:underline">
https://bugreport.java.com/bugreport/</a></div>
<div><br>
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<div>Regards,</div>
<div><br>
</div>
<div>-Joe</div>
<div><br>
</div>
<div>On 10/22/2025 3:45 PM, 徐佳 wrote:<br>
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<div style="font-size:13px">Hi,</div>
<pre style="margin-top:0px; margin-bottom:0px"><div><span style="line-height:1.5"><code>Despite having an idle worker, the submitted task did not run.</code></span></div></pre>
<pre style="margin-top:0px; margin-bottom:0px"><div>Steps to reproduce:</div></pre>
<pre style="margin-top:0px; margin-bottom:0px"><div style="font-size:13px"><span style="line-height:1.5"><code>-------------------</code></span></div></pre>
<pre style="margin-top:0px; margin-bottom:0px"><div style="font-size:13px"><span style="line-height:1.5"><code>1. before all , add a breakpoint on the 1864th line of ForkJoinPool source code in awaitWork method.</code></span></div></pre>
<pre style="margin-top:0px; margin-bottom:0px"><div><span style="font-size:13px; line-height:1.5"><code>2. then debug the following code，and a thread will be </code></span>paused at breakpoint</div></pre>
<pre style="margin-top:0px; margin-bottom:0px"><div><span style="font-size:13px; line-height:1.5"><code>3. after "</code></span>submited task2" printed in the console<span style="font-size:12px; color:rgb(69,69,69)">, </span>resume the breakpoint.</div></pre>
<pre style="margin-top:0px; margin-bottom:0px"><div>4. Despite having an idle worker, task2 did not run.</div></pre>
<pre style="margin-top:0px; margin-bottom:0px"><p style="line-height:normal; white-space:normal; margin:0px; font-size:12px; color:rgb(69,69,69)"><span style="line-height:1.5"><b><code>public</code></b><code> </code><b><code>class</code></b><code> ForkJoinPoolTest {</code></span></p><p style="line-height:normal; white-space:normal; margin:0px; font-size:12px; color:rgb(69,69,69)"><span style="line-height:1.5"><b><code>public</code></b><code> </code><b><code>static</code></b><code> </code><b><code>void</code></b><code> main</code></span><span style="line-height:normal"><code>(</code></span><span style="line-height:1.5"><code>String</code></span><span style="line-height:normal"><code>[]</code></span><span style="line-height:1.5"><code> args</code></span><span style="line-height:normal"><code>)</code></span><span style="line-height:1.5"><code> </code><b><code>throws</code></b><code> InterruptedException {</code></span></p><p style="line-height:normal; white-space:normal; margin:0px; font-size:12px; color:rgb(69,69,69)"><span style="line-height:1.5"><code>//Add a breakpoint on the 1864th line of ForkJoinPool source code in awaitWork method.</code></span></p><p style="line-height:normal; white-space:normal; margin:0px; min-height:14px; font-size:12px; color:rgb(69,69,69)"><span style="line-height:1.5"><code><
span class="Apple-tab-span" style="white-space: pre;"> </code></span></p><p style="line-height:normal; white-space:normal; margin:0px; font-size:12px; color:rgb(69,69,69)"><span style="line-height:1.5"><code>ForkJoinPool pool = </code><b><code>new</code></b><code> ForkJoinPool</code></span><span style="line-height:normal"><code>(</code></span><span style="line-height:1.5"><code>2</code></span><span style="line-height:normal"><code>);</code></span><span style="line-height:1.5"><code>//total 2 Threads</code></span></p><p style="line-height:normal; white-space:normal; margin:0px; font-size:12px; color:rgb(69,69,69)"><span style="line-height:1.5"><code>//create worker w1</code></span><span style="line-height:normal"><code>,</code></span><span style="line-height:1.5"><code> keep running and printing pool information</code></span></p><p style="line-height:normal; white-space:normal; margin:0px; font-size:12px; color:rgb(69,69,69)"><span style="line-height:1.5"><code>pool.submit</code></span><span style="line-height:normal"><code>(()</code></span><span style="line-height:1.5"><code> -> {</code></span></p><p style="line-height:normal; white-space:normal; margin:0px; font-size:12px; color:rgb(69,69,69)"><span style="line-height:1.5"><b><code>while</code></b></span><span style="line-height:normal"><code>(</code></span><span style="line-height:1.5"><b><code>true</code></b></span><span style="line-height:normal"><code>)</code></span><span style="line-height:1.5"><code> {</code></span></p><p style="line-height:normal; white-space:normal; margin:0px; font-size:12px; color:rgb(69,69,69)"><span style="line-height:1.5"><code>System.</code><b><i><code>err</code></i></b><code>.println</code></span><span style="line-height:normal"><code>(</code></span><span style="line-height:1.5"><code>"==================="</code></span><span style="line-height:normal"><code>);</code></span></p><p style="line-height:normal; white-space:normal; margin:0px; color:rgb(69,69,69)"><span style="font-size:13px; line-height:1.5"><code>System.</code><b><i><code>err</code></i></b><code>.println</code></span><span style="font-size:13px; line-height:normal"><code>(</code></span><span style="font-size:13px; line-height:1.5"><code>"QueuedSubmissionCount:" + pool.getQueuedSubmissionCount());</code></span></p><p style="line-height:normal; white-space:normal; margin:0px; font-size:12px; color:rgb(69,69,69)"><span style="line-height:1.5"><code>System.</code><b><i><code>err</code></i></b><code>.println</code></span><span style="line-height:normal"><code>(</code></span><span style="line-height:1.5"><code>"ActiveThreadCount:" + pool.getActiv
eThreadCount</code></span><span style="line-height:normal"><code>());</code></span></p><p style="line-height:normal; white-space:normal; margin:0px; font-size:12px; color:rgb(69,69,69)"><span style="line-height:1.5"><code>System.</code><b><i><code>err</code></i></b><code>.println</code></span><span style="line-height:normal"><code>(</code></span><span style="line-height:1.5"><code>"PoolSize:" + pool.getPoolSize</code></span><span style="line-height:normal"><code>());</code></span></p><p style="line-height:normal; white-space:normal; margin:0px; font-size:12px; color:rgb(69,69,69)"><span style="line-height:1.5"><code>System.</code><b><i><code>err</code></i></b><code>.println</code></span><span style="line-height:normal"><code>(</code></span><span style="line-height:1.5"><code>"==================="</code></span><span style="line-height:normal"><code>);</code></span></p><p style="line-height:normal; white-space:normal; margin:0px; font-size:12px; color:rgb(69,69,69)"><span style="line-height:1.5"><code>LockSupport.</code><i><code>parkNanos</code></i></span><span style="line-height:normal"><code>(</code></span><span style="line-height:1.5"><code>5 * 1000_000_000L</code></span><span style="line-height:normal"><code>);</code></span><span style="line-height:1.5"><code>//5s</code></span></p><p style="line-height:normal; white-space:normal; margin:0px; font-size:12px; color:rgb(69,69,69)"><span style="line-height:1.5"><code>}</code></span></p><p style="line-height:normal; white-space:normal; margin:0px; font-size:12px; color:rgb(69,69,69)"><span style="line-height:1.5"><code>});</code></span></p><p style="line-height:normal; white-space:normal; margin:0px; font-size:12px; color:rgb(69,69,69)"><span style="line-height:1.5"><code>//create another worker w2</code></span></p><p style="line-height:normal; white-space:normal; margin:0px; font-size:12px; color:rgb(69,69,69)"><span style="line-height:1.5"><code>pool.submit</code></span><span style="line-height:normal"><code>(()</code></span><span style="line-height:1.5"><code> -> System.</code><b><i><code>out</code></i></b><code>.println</code></span><span style="line-height:normal"><code>(</code></span><span style="line-height:1.5"><code>Thread.</code><i><code>currentThread</code></i></span><span style="line-height:normal"><code>()</code></span><span style="line-height:1.5"><code>.getName</code></span><span style="line-height:normal"><code>()</code></span><span style="line-height:1.5"><code> + " : finished task1"</code></span><span style="line-height:normal"><code>));</code></span></p><p style="line-height:normal; white-space:normal; margin:0px; font-size:12px; color:rgb(69,69,69)"><span style="line-height:1.5"><code>System.</code><b><i><code>out</code></i></b><code>.println</code></span><span style="line-height:normal"><code>(</code></span><span style="line-height:1.5"><code>"submited task1"</code></span><span style="line-height:normal"><code>);</code></span></p><p style="line-height:normal; white-space:normal; margin:0px; font-size:12px; color:rgb(69,69,69)"><span style="line-height:1.5"><code>Thread.</code><i><code>sleep</code></i></span><span style="line-height:normal"><code>(</code></span><span style="line-height:1.5"><code>3 * 1000</code></span><span style="line-height:normal"><code>);</code></span><span style="line-height:1.5"><code>// waiting for task1 to end</code></span></p><p style="line-height:normal; white-space:normal; margin:0px; font-size:12px; color:rgb(69,69,69)"><span style="line-height:1.5"><code>//now task1 finished and no task in queue</code></span><span style="line-height:normal"><code>,</code></span><span style="line-height:1.5"><code> w2 is pausing at breakpoint in awaitWork method.</code></span></p><p style="line-height:normal; white-space:normal; margin:0px; font-size:12px; color:rgb(69,69,69)"><span style="line-height:1.5"><code>pool.submit</code></span><span style="line-height:normal"><code>(()</code></span><span style="line-height:1.5"><code> -> System.</code><b><i><code>out</code></i></b><code>.println</code></span><span style="line-height:normal"><code>(</code></span><span style="line-height:1.5"><code>Thread.</code><i><code>currentThread</code></i></span><span style="line-height:normal"><code>()</code></span><span style="line-height:1.5"><code>.getName</code></span><span style="line-height:normal"><code>()</code></span><span style="line-height:1.5"><code> + " : fin
ished task2"</code></span><span style="line-height:normal"><code>));</code></span></p><p style="line-height:normal; white-space:normal; margin:0px; font-size:12px; color:rgb(69,69,69)"><span style="line-height:1.5"><code>System.</code><b><i><code>out</code></i></b><code>.println</code></span><span style="line-height:normal"><code>(</code></span><span style="line-height:1.5"><code>"submited task2"</code></span><span style="line-height:normal"><code>);</code></span></p><p style="line-height:normal; white-space:normal; margin:0px; font-size:12px; color:rgb(69,69,69)"><span style="line-height:1.5"><code>//after submitted task2</code></span><span style="line-height:normal"><code>,</code></span><span style="line-height:1.5"><code> resume w2 </code></span><span style="line-height:normal"><code>,</code></span><span style="line-height:1.5"><code> and then w2 will park on line 1891 </code></span><span style="line-height:normal"><code>,</code></span><span style="line-height:1.5"><code>although there is still task2 in the Submission queue </code></span></p><p style="line-height:normal; white-space:normal; margin:0px; font-size:12px; color:rgb(69,69,69)"><span style="line-height:1.5"><code>//if no new task submitted</code></span><span style="line-height:normal"><code>,</code></span><span style="line-height:1.5"><code> task2 will not run.</code></span></p><p style="line-height:normal; white-space:normal; margin:0px; font-size:12px; color:rgb(69,69,69)"><span style="line-height:1.5"><code>Thread.</code><i><code>sleep</code></i></span><span style="line-height:normal"><code>(</code></span><span style="line-height:1.5"><code>5 * 60 * 1000</code></span><span style="line-height:normal"><code>);</code></span></p><p style="line-height:normal; white-space:normal; margin:0px; font-size:12px; color:rgb(69,69,69)"><span style="line-height:1.5"><code>pool.close</code></span><span style="line-height:normal"><code>();</code></span></p><p style="line-height:normal; white-space:normal; margin:0px; font-size:12px; color:rgb(69,69,69)"><span style="line-height:1.5"><code>}</code></span></p><p style="line-height:normal; white-space:normal; margin:0px; font-size:12px; color:rgb(69,69,69)"><span style="line-height:1.5"><code>}</code></span></p><pre style="margin-top:0px; margin-bottom:0px"><div style="font-size:13px"><span style="line-height:1.5"><code>
</code></span></div></pre><div style="font-size:13px"><span style="line-height:1.5"><code>result:</code></span></div></pre>
<pre style="margin-top:0px; margin-bottom:0px"><div style="font-size:13px"><span style="line-height:1.5"><code>
<img id="x_x_img_insert_1761144985303033518428439668657" width="339" height="388" style="vertical-align:bottom; width:339px; height:388px" data-outlook-trace="F:2|T:2" src="cid:F8FE61C2@8FD16500.0825FA6800000000.jpg">
Environment:
------------
</code></span></div><p style="line-height:normal; white-space:normal; margin:0px; font-family:Menlo; font-size:11px"><span style="line-height:1.5"><code>java version "21.0.8" 2025-07-15 LTS</code></span></p><p style="line-height:normal; white-space:normal; margin:0px; font-family:Menlo; font-size:11px"><span style="line-height:1.5"><code>Java(TM) SE Runtime Environment (build 21.0.8+12-LTS-250)</code></span></p><p style="line-height:normal; white-space:normal; margin:0px; font-family:Menlo; font-size:11px"><span style="line-height:1.5"><code>Java HotSpot(TM) 64-Bit Server VM (build 21.0.8+12-LTS-250, mixed mode, sharing)</code></span></p><div style="font-size:13px"><span style="line-height:1.5"><code>it seams that a task submitted between method “scan”and “awaitWork” may not be executed immediately</code></span></div></pre>
<pre style="margin-top:0px; margin-bottom:0px"><div><span style="font-size:13px; line-height:1.5"><code>I think the reason is that the worker did not recheck the waiting condition "</code></span>hasTasks<span style="font-size:13px; line-height:1.5"><code>" between "</code></span>enqueue<span style="font-size:13px; line-height:1.5"><code>" and "</code></span>park"</div></pre>
<pre style="margin-top:0px; margin-bottom:0px"><div>I don't know whether this is a bug or it's just designed this way</div></pre>
<pre style="margin-top:0px; margin-bottom:0px"><div style="font-size:13px"><span style="line-height:1.5"><code>
Please let me know if more information is needed.
Thanks,
Jia Xu</code></span></div></pre>
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