https://xinqilin.github.io/tags/project-loom/ Recent content in Project Loom on Bill.Lin's Notes Hugo zh-tw Mon, 15 Jan 2024 00:00:00 +0800 https://xinqilin.github.io/post/backend/spring-virtual-threads/ Mon, 15 Jan 2024 00:00:00 +0800 https://xinqilin.github.io/post/backend/spring-virtual-threads/ <h2 id="什麼是-virtual-threads">什麼是 Virtual Threads</h2> <p>Java 21 正式引入 Virtual Threads（Project Loom），目的是讓 <strong>I/O-bound</strong> 的應用在不改變同步程式碼風格的前提下，獲得接近非同步的吞吐量。</p> <h3 id="carrier-thread-vs-virtual-thread--mn-調度">Carrier Thread vs Virtual Thread — M:N 調度</h3> <div class="highlight"><div class="chroma"> <table class="lntable"><tr><td class="lntd"> <pre tabindex="0" class="chroma"><code><span class="lnt">1 </span><span class="lnt">2 </span><span class="lnt">3 </span><span class="lnt">4 </span><span class="lnt">5 </span></code></pre></td> <td class="lntd"> <pre tabindex="0" class="chroma"><code class="language-fallback" data-lang="fallback"><span class="line"><span class="cl">OS Thread (Carrier Thread) [N 條] </span></span><span class="line"><span class="cl"> │ </span></span><span class="line"><span class="cl"> ├── Virtual Thread 1 (執行中) </span></span><span class="line"><span class="cl"> ├── Virtual Thread 2 (等待 I/O，已卸載) </span></span><span class="line"><span class="cl"> └── Virtual Thread 3 (等待 I/O，已卸載) </span></span></code></pre></td></tr></table> </div> </div><ul> <li><strong>Platform Thread（傳統）</strong>：1:1 對應 OS thread，每條佔 ~1MB stack，數量上限約數千條。</li> <li><strong>Virtual Thread</strong>：M:N，大量 virtual threads 映射到少量 carrier threads（通常等於 CPU cores）。</li> <li>當 virtual thread 遇到阻塞 I/O，JVM <strong>自動將它從 carrier thread 卸載（unmount）</strong>，carrier thread 可繼續處理其他 virtual threads；I/O 完成後再重新掛載（mount）。</li> </ul> <p>這讓你可以為每個 HTTP 請求建立一條 virtual thread，而不用擔心耗盡 OS threads。</p>