Heikki suggested that we backport atomic operation from PostgreSQL 9.5 to
fix this

    commit b64d92f1
    Author: Andres Freund <andres@anarazel.de>
    Date:   Thu Sep 25 23:49:05 2014 +0200

    Add a basic atomic ops API abstracting away platform/architecture details.

    Several upcoming performance/scalability improvements require atomic
    operations. This new API avoids the need to splatter compiler and
    architecture dependent code over all the locations employing atomic
    ops.

    For several of the potential usages it'd be problematic to maintain
    both, a atomics using implementation and one using spinlocks or
    similar. In all likelihood one of the implementations would not get
    tested regularly under concurrency. To avoid that scenario the new API
    provides a automatic fallback of atomic operations to spinlocks. All
    properties of atomic operations are maintained. This fallback -
    obviously - isn't as fast as just using atomic ops, but it's not bad
    either. For one of the future users the atomics ontop spinlocks
    implementation was actually slightly faster than the old purely
    spinlock using implementation. That's important because it reduces the
    fear of regressing older platforms when improving the scalability for
    new ones.

    The API, loosely modeled after the C11 atomics support, currently
    provides 'atomic flags' and 32 bit unsigned integers. If the platform
    efficiently supports atomic 64 bit unsigned integers those are also
    provided.

    To implement atomics support for a platform/architecture/compiler for
    a type of atomics 32bit compare and exchange needs to be
    implemented. If available and more efficient native support for flags,
    32 bit atomic addition, and corresponding 64 bit operations may also
    be provided. Additional useful atomic operations are implemented
    generically ontop of these.

    The implementation for various versions of gcc, msvc and sun studio have
    been tested. Additional existing stub implementations for
    * Intel icc
    * HUPX acc
    * IBM xlc
    are included but have never been tested. These will likely require
    fixes based on buildfarm and user feedback.

    As atomic operations also require barriers for some operations the
    existing barrier support has been moved into the atomics code.

    Author: Andres Freund with contributions from Oskari Saarenmaa
    Reviewed-By: Amit Kapila, Robert Haas, Heikki Linnakangas and Álvaro Herrera
    Discussion: CA+TgmoYBW+ux5-8Ja=Mcyuy8=VXAnVRHp3Kess6Pn3DMXAPAEA@mail.gmail.com,
        20131015123303.GH5300@awork2.anarazel.de,
        20131028205522.GI20248@awork2.anarazel.de