A Study of Memory Anomalies in OpenMP Applications

Abstract

Incorrect usage of OpenMP constructs may cause different kinds of defects in OpenMP applications. Most of the existing work focuses on concurrency bugs such as data races and deadlocks, since concurrency bugs are difficult to detect and debug. In this paper, we discuss an under-examined defect in OpenMP applications: memory anomalies. These occur when the application issues illegal memory accesses that may result in a non-deterministic result or even a program crash. Based on the latest OpenMP 5.0 specification, we analyze some OpenMP usage errors that may lead to memory anomalies. Then we illustrate three kinds of memory anomalies: use of uninitialized memory (UUM), use of stale data (USD), and use after free (UAF). While all three anomalies can occur in sequential programs, their manifestations in parallel OpenMP programs can be different, and debugging such anomalies in the context of parallel programs also imposes an additional complexity relative to sequential programs. To measure the effectiveness of memory anomaly detectors on OpenMP applications, we have evaluated three state-of-the-art tools with a group of micro-benchmarks. These micro-benchmarks are either selected from the DRACC benchmark suite or constructed from our own experience. The evaluation result shows that none of these tools can currently handle all three kinds of memory anomalies.