A buffer is a queue of characters that are ready to write. When there are enough characters in the queue, they are all written together in one operation.
的字符缓冲区队列已经准备好写。当队列中有足够的人物,他们都是写在一个操作。
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The reason you only use OP_WRITE like this is that is almost always ready (because there is almost always space in the socket send buffer), but you aren't almost always ready to write.