ZAPP

Zero Assignment Parallel Processor. A virtual tree machine

architecture in which a process tree is dynamically mapped

onto a fixed, strongly connected network of processors

communicating by message passing. The basic operation of each

node is to apply a divide and conquer function which takes

four arguments: (1) a function 'primitive' which takes a

problem description (PD) and returns true if it can be solved

without division, (2) a function 'solve' which takes a

primitive PD and returns its solution, (3) a function 'divide'

which takes a PD and returns a list of PDs of smaller problems

and (4) a function 'combine' which returns the solution to a

problem by combining a list of solutions of subproblems.

Each node has a copy of the code and one is given the initial

problem description. Task distribution is by process stealing

in which a process constructs a descriptor for each subtask

and idle (lightly loaded) processors can steal a descriptor

from a physically connected neighbour.