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Parallator
1. Introduction
Figure 1.9.: The programmer selects the bodies array and Convert To Parallel Array refactoring. ReLooper converts the sequential loops (left-hand side) into parallel
loops (right-hand side) using the ParallelArray framework [DD12].
ReLooper uses a data-flow analysis that determines objects that are shared among loop
iterations, and detects writes to the shared objects. This static analysis is based on the
SSA (single static assignment) intermediate representation of a program and it analyzes
both, the program in source code and in byte code. Additionally the data-flow analysis
is conservative, it could give false warnings. Therefore it is crucial that the refactoring
is interactive. The user as expert can decide whether to move on even though warnings
exist. The decision to parallelize and ignore the warnings can be done for every loop in
the example of figure 1.9.
1.6. Project Goals
TBB provides a rich set of threading building blocks that help in parallelize sequential
algorithms. They provide an abstraction to parallelize operations on loop elements with
different kind of dependencies. A manual conversion of the loops into parallelized TBB
calls is time consuming, error prone and enforces advanced knowledge as of the following
reasons:
ˆ Finding loops that provide data or task parallelism is difficult. It requires a conscious
analysis of the code.
ˆ The manual transformation to parallelism can introduce errors. Especially if knowledge of lambda expressions and functors is not well-founded. Whether to pass a
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