• Philippe Gerum's avatar
    evl: add stage exclusion lock mechanism · 6c19d25f
    Philippe Gerum authored
    
    
    A STAge eXclusion lock (aka stax) serializes in-band vs out-of-band
    thread activities for accessing a resource. Multiple threads which run
    on the same execution stage can own the resource concurrently, threads
    from the converse stage have to wait until the last thread dropped the
    innermost lock. In other words, at any point in time, the resource is
    either:
    
    - owned by out-of-band threads exclusively
    - owned by in-band threads exclusively
    - not owned by any thread
    
    Sleeping while owning a stax whether from the in-band or out-of-band
    stage is ok, although this may defer threads running on the converse
    stage which may want to access the same resource. For this reason, a
    stax is definitely not designed for guaranteeing low latency to
    out-of-band threads, but merely as a way to allow safe sharing of some
    resource between both stages in case strictly reserving access to
    out-of-band threads by construction is not a practical option.
    
    Other serialization means such as mutexes (either regular in-band ones
    or EVL) should be used to enforce mutual exclusion among threads
    running on the same stage which may still concurrently run through a
    staxed section.
    Signed-off-by: Philippe Gerum's avatarPhilippe Gerum <rpm@xenomai.org>
    6c19d25f
control.h 767 Bytes