  The LIGO, VIRGO and KAGRA Gravitational-wave (GW) observatories are getting
ready for their fourth observational period, O4, scheduled to begin in March
2023, with improved sensitivities and thus higher event rates. GW-related
computing has both large commonalities with HEP computing, particularly in the
domain of offline data processing and analysis, and important differences, for
example in the fact that the amount of raw data doesn't grow much with the
instrument sensitivity, or the need to timely generate and distribute "event
candidate alerts" to EM and neutrino observatories, thus making gravitational
multi-messenger astronomy possible. Data from the interferometers are exchanged
between collaborations both for low-latency and offline processing; in recent
years, the three collaborations designed and built a common distributed
computing infrastructure to prepare for a growing computing demand, and to
reduce the maintenance burden of legacy custom-made tools, by increasingly
adopting tools and architectures originally developed in the context of HEP
computing. So, for example, HTCondor is used for workflow management, Rucio for
many data management needs, CVMFS for code and data distribution, and more. We
will present GW computing use cases and report about the architecture of the
computing infrastructure as will be used during O4, as well as some planned
upgrades for the subsequent observing run O5.
