UV_THREADPOOL_SIZE=size

将 libuv 的线程池中使用的线程数设置为 size 个线程。

¥Set the number of threads used in libuv's threadpool to size threads.

Node.js 尽可能使用异步的系统 API，但在它们不存在的情况下，libuv 的线程池用于基于同步的系统 API 创建异步的 node API。使用线程池的 Node.js API 有：

¥Asynchronous system APIs are used by Node.js whenever possible, but where they do not exist, libuv's threadpool is used to create asynchronous node APIs based on synchronous system APIs. Node.js APIs that use the threadpool are:

• 所有 fs API，除了文件监视器 API 和那些显式同步的

  ¥all fs APIs, other than the file watcher APIs and those that are explicitly synchronous

• 异步加密 API，例如 crypto.pbkdf2()、crypto.scrypt()、crypto.randomBytes()、crypto.randomFill()、crypto.generateKeyPair()

  ¥asynchronous crypto APIs such as crypto.pbkdf2(), crypto.scrypt(), crypto.randomBytes(), crypto.randomFill(), crypto.generateKeyPair()

• dns.lookup()

• 所有 zlib API，除了那些显式同步的

  ¥all zlib APIs, other than those that are explicitly synchronous

因为 libuv 的线程池有固定的大小，这意味着如果这些 API 中的任何一个由于某种原因需要很长时间，则在 libuv 的线程池中运行的其他（看似无关的）API 的性能将会下降。为了缓解此问题，潜在的解决方案是通过将 'UV_THREADPOOL_SIZE' 环境变量设置为大于 4（其当前默认值）的值来增加 libuv 线程池的大小。但是，使用 process.env.UV_THREADPOOL_SIZE=size 从进程内部设置此项并不能保证有效，因为线程池将在运行用户代码之前作为运行时初始化的一部分创建。有关详细信息，请参阅 libuv 线程池文档。

¥Because libuv's threadpool has a fixed size, it means that if for whatever reason any of these APIs takes a long time, other (seemingly unrelated) APIs that run in libuv's threadpool will experience degraded performance. In order to mitigate this issue, one potential solution is to increase the size of libuv's threadpool by setting the 'UV_THREADPOOL_SIZE' environment variable to a value greater than 4 (its current default value). However, setting this from inside the process using process.env.UV_THREADPOOL_SIZE=size is not guranteed to work as the threadpool would have been created as part of the runtime initialisation much before user code is run. For more information, see the libuv threadpool documentation.