A Non-Deadlock Time Management Algorithm in HLA

HLA (high level architecture) is the standard for modeling and simulation put forward by the American Department of Defense. Time management is an important component of HLA while GALT (greatest available logical time) algorithm is RTI (runtime infrastructure) critical technology in implementing time management. An improper GALT algorithm can easily result in a deadlock so that the whole federation can not advance any more. On the basis of the GALT algorithm introduced by Frederick Kuhl, the principles of deadlock are discussed and some important results are gotten. If deadlock occurs in a simulation, all federates must have the same GALT and the same output time respectively, and their GALTs are also equal to output-time. A federate whose lookahead value is larger than zero must be pended because of a NMR or NMRA request, but not a TAR, TARA or FQR service. Finally, a GALT algorithm called strict order algorithm without deadlock is put forward. And this algorithm can provide reliable technology support to develop time management services of RTI.