• Dridi Boukelmoune's avatar
    vca: Have one inheritance check per listen socket · 4eeb1e25
    Dridi Boukelmoune authored
    Instead of having a single global check that all acceptors may race
    towards, this check now happens on a per listen socket basis. For
    sockets with a different inheritance behavior on a single system, we
    avoid having the first connection dictate what may be inherited by
    a connection socket from its listen socket for all the other listen
    addresses.
    
    At least on Linux, Unix-domain sockets DO NOT inherit options like
    SO_{RCV,SND}TIMEO even though TCP sockets do. On the off chance that
    even sockets of the same family could behave differently, like for
    example a regular vs a loopback TCP session, this is done on a per
    listen address basis. To avoid cache-acceptor coordination with the
    acceptor worker threads of a given listen address, workers will
    individually perform this check once and for all when the first
    connection is accepted.
    
    We also stay defensive in the event of a parameter change, just in
    case a previous test would assume inheritance because the Varnish
    parameter value would match the kernel default value. Once a mismatch
    is observed for a given connection with a given socket, the inheritance
    test is no longer performed needlessly for this combination.
    
    A race still exists between acceptors from different thread pools for
    a given listen address, but this race is identical to the previous one
    based on the former global need_test variable.
    
    Although the inheritance check leaks into struct listen_sock, it is
    opaque so everything can remain contained inside cache_acceptor.c.
    
    Some aspects of this change (including the clarification comments) are
    from @mbgrydeland.
    
    Refs #2722
    4eeb1e25
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