SIGIO only mean readable or writable, how channel event avoid writable

[yang chen]

[image: 内嵌图片 1]

in the "Linux System Programming: Talking Directly to the Kernel and C
Library", it says SIGIO mean readable or writable, and in man page it says
SIGIO means I/O is possible on a descriptor,
so if this, I'm curious that channel is writable, nginx will receive the
SIGIO?
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