Summary: Fast Timingbased Algorithms \Lambda
Rajeev Alur y Gadi Taubenfeld z
Concurrent systems in which there is a known upper bound \Delta on memory access time
are considered. Two prototypical synchronization problems, mutual exclusion and con
sensus, are studied and solutions that have constant (i.e. independent of \Delta and the
total number of processes) time complexity in the absence of contention are presented.
For mutual exclusion, in the absence of contention, a process needs only five accesses to
the shared memory to enter its critical section, and in the presence of contention, the
winning process may need to delay itself for 4 \Delta \Delta time units. For consensus, in absence
of contention, a process decides after four accesses to the shared memory, and in the
presence of contention, it may need to delay itself for \Delta time units.
The possibility and complexity of synchronization in a distributed environment depends
heavily on timing assumptions. In the asynchronous model no timing assumptions are
made about the relative speeds of the processes, while a timingbased model assumes known
bounds on the speeds of the processes. In this paper, we study two prototypical coordination
and synchronization problems, namely, mutual exclusion and consensus, in the latter model.
We use a shared memory model where processes communicate with each other by reading
and writing to shared registers. We assume that there is an upper bound, denoted by \Delta,