<ul class="contains-task-list">
<li class="task-list-item"><input type="checkbox" id="" disabled="" class="task-list-item-checkbox" checked=""> I have searched the <a href="https://github.com/apache/incubator-dubbo/issues">issues</a> of this repository and believe that this is not a duplicate.</li>
<li class="task-list-item"><input type="checkbox" id="" disabled="" class="task-list-item-checkbox" checked=""> I have checked the <a href="https://github.com/apache/incubator-dubbo/blob/master/FAQ.md">FAQ</a> of this repository and believe that this is not a duplicate.</li>
</ul>
<h3 dir="auto">Environment</h3>
<ul dir="auto">
<li>Dubbo version: 2.7.0-SNAPSHOT</li>
</ul>
<h3 dir="auto">Steps to reproduce this issue</h3>
<p dir="auto"><a href="https://github.com/apache/incubator-dubbo/blob/7f926d9991ba69dba25b56925e4cc5ffcdf50afa/dubbo-cluster/src/main/java/org/apache/dubbo/rpc/cluster/support/ForkingClusterInvoker.java#L68-L75">Source code Fragment</a>:</p>
<div class="highlight highlight-source-java notranslate position-relative overflow-auto" dir="auto" data-snippet-clipboard-copy-content="for (int i = 0; i &lt; forks; i++) {
    // TODO. Add some comment here, refer chinese version for more details.
    Invoker&lt;T&gt; invoker = select(loadbalance, invocation, invokers, selected);
    if (!selected.contains(invoker)) {
        //Avoid add the same invoker several times.
        selected.add(invoker);
    }
}"><pre class="notranslate"><span class="pl-k">for</span> (<span class="pl-smi">int</span> <span class="pl-s1">i</span> = <span class="pl-c1">0</span>; <span class="pl-s1">i</span> &lt; <span class="pl-s1">forks</span>; <span class="pl-s1">i</span>++) {
    <span class="pl-c">// TODO. Add some comment here, refer chinese version for more details.</span>
    <span class="pl-smi">Invoker</span>&lt;<span class="pl-smi">T</span>&gt; <span class="pl-s1">invoker</span> = <span class="pl-en">select</span>(<span class="pl-s1">loadbalance</span>, <span class="pl-s1">invocation</span>, <span class="pl-s1">invokers</span>, <span class="pl-s1">selected</span>);
    <span class="pl-k">if</span> (!<span class="pl-s1">selected</span>.<span class="pl-en">contains</span>(<span class="pl-s1">invoker</span>)) {
        <span class="pl-c">//Avoid add the same invoker several times.</span>
        <span class="pl-s1">selected</span>.<span class="pl-en">add</span>(<span class="pl-s1">invoker</span>);
    }
}</pre></div>
<p dir="auto">When <code class="notranslate">selected list</code> contains invoker, it will continue loop, it may result in the size of <code class="notranslate">selected list</code> less than <code class="notranslate">forks</code>.</p>
<ul class="contains-task-list">
<li class="task-list-item"><input type="checkbox" id="" disabled="" class="task-list-item-checkbox" checked=""> I have searched the <a href="https://github.com/apache/incubator-dubbo/issues">issues</a> of this repository and believe that this is not a duplicate.</li>
<li class="task-list-item"><input type="checkbox" id="" disabled="" class="task-list-item-checkbox" checked=""> I have checked the <a href="https://github.com/apache/incubator-dubbo/blob/master/FAQ.md">FAQ</a> of this repository and believe that this is not a duplicate.</li>
</ul>
<h3 dir="auto">Environment</h3>
<ul dir="auto">
<li>Dubbo version: 2.6.2</li>
<li>Operating System version: mac os</li>
<li>Java version: 1.8</li>
</ul>
<h3 dir="auto">Steps to reproduce this issue</h3>
<p dir="auto">com.alibaba.dubbo.common.Constants#DEFAULT_SERVER_SHUTDOWN_TIMEOUT，<br>
I think this number is too big，2~3 second  is enough。</p>
<h3 dir="auto">Expected Result</h3>
<p dir="auto">make a small default value 。</p>
<h3 dir="auto">Actual Result</h3>
<p dir="auto">What actually happens?</p>
<p dir="auto">If there is an exception, please attach the exception trace:</p>