Issue #4680 has been reported by Eric Wong.

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Bug #4680: [PATCH] io.c: fix busy wait with sendfile()
http://redmine.ruby-lang.org/issues/4680

Author: Eric Wong
Status: Open
Priority: Normal
Assignee: 
Category: core
Target version: 1.9.3
ruby -v: ruby 1.9.3dev (2011-05-11 trunk 31521) [x86_64-linux]


io.c: fix busy wait with sendfile()

When combined with a non-blocking descriptor for sendfile(),
select() is used improperly to wait on the writer in the
read FD set along with the reader.

This causes select() to return immediately if src_fd is a
regular file and select() always returns immediately for regular
files (at least under Linux).

Thus, we need to wait on the writer independently of the reader.
Under Linux, we know the reader must must be a regular file if
sendfile() is to be used so we avoid waiting on the reader.

Test script attached maxes out my CPU.



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