DOC: internals: document the FD takeover process

This explains the traps to avoid and the sequence that leads to
consistent use of an FD known by multiple threads at once. This
was co-authored with Olivier.

(cherry picked from commit 88babd99443b82bd3b9a8074ceddc211e64d139f)
Signed-off-by: Willy Tarreau <w@1wt.eu>
1 file changed