• Martin Blix Grydeland's avatar
    Rework HSH_Purge() · e51208cb
    Martin Blix Grydeland authored
    HSH_Purge() suffers from a problem when there are more objcores on a given
    objhead than we can hold temporary references for on the available
    workspace, and multiple purges for the same objhead are issued at the same
    time.
    
    The previous algorithm would use a flag on the objcores (OC_F_PURGED) in
    order to keep track of how far in the list we had gotten. This becomes a
    problem when multiple threads are purging the same objhead at the same
    time. When a new purge is started, the flags would be reset, which would
    cause any existing purge thread to restart. If a steady stream of purges
    for a given objhead is issued and enough objcores are present, none would
    finish.
    
    This rework uses OC references in the list as bookmarks, in order to know
    how far into the list we were when releasing the mutex partway through and
    want to resume again. This relies on the list not being reordered while we
    are not holding the mutex. The only place where that happens is in
    HSH_Unbusy(), where an OC_F_BUSY OC is moved first in the list. This does
    not cause problems because we skip OC_F_BUSY OCs.
    
    The OC_F_PURGED flag is removed as it is no longer needed.
    
    The existing r02372.vtc test case exercises this code.
    e51208cb
oc_flags.h 1.71 KB