my $line = <STDIN> || q{};

You introduced bugs by moving away from sysread.

First, you've introduced buffered IO. How can the select system call know that Perl has data waiting to be read in a buffer?

Second, you're blocking until a newline is received, and that could be an indefinitely long wait.

In reply to Re^2: Non-blocking I/O woes by ikegami
in thread Non-blocking I/O woes by dwalin

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