Efficient programming of task-parallel problems, where the number and
execution times of the computational tasks can vary unpredictably, demands
an asynchronous and adaptive approach.  In this sort of approach, however,
such fundamental programming issues as load sharing, data sharing,
and termination detection can present difficult programming problems.
This paper presents the PMESC library for managing task-parallel problems
on distributed-memory MIMD computers within the context of the SPMD
(Single Program, Multiple Data) programming model.  PMESC offers support
for all of the application-independent programming issues involved in SPMD
task-parallel computation in a portable and efficient way while still
allowing users to customize their codes.  Because different problems
may require different strategies to achieve good performance,  PMESC is
based on a straightforward model in which different building blocks can
be easily put together and changed to accommodate the particular needs
of the different applications.  The library provides an interface that
allows users to program a virtual machine and thereby ignore the details
associated with message passing and machine architecture. These features
make PMESC accessible to a wide variety of users.