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SDPOR Testing Multithreaded C Programs with
Dynamic Partial Order Reduction and State
Capture Yu Yang, Xiaofang Chen, Ganesh
Gopalakrishnan, Robert M. Kirby School of
Computing, University of Utah, Salt Lake City, UT
84112 http//www.cs.utah.edu/formal_verification
Stateful Dynamic Partial Order Reduction
Motivation

• Naïvely backtracking when encountering a visited
  
• state may result in missed backtracking points

• Concurrency bugs lurk within unexamined paths
• Stateless model checking with dynamic partial
• order reduction works well for small thread
• programs
• We offer method to capture thread-local states,
• which, in turn, helps reduce redundant searches
  

• Our solution -- summarizing the state-space
  using
• a transition dependency graph. The summary is
  
• not associated with each state. Instead, it is
• computed dynamically when a visited state is
• encountered.

A Simple Example

• thread 1
• for (i 0 i lt100i)
• lock(x)
• data
• assert(data5 ! 4)
• unlock(x)

thread 2 for (j 0 j lt100i) lock(x)
data-j assert(data5!2) unlock(x)
Implementation

• 200! / (100! 100!) interleavings will be
  explored
• with stateless search, even when dynamic
  partial
• order reduction is enabled (i.e. no
  reductions!)

An Alternative State Capturing Scheme

• Local states of threads are treated as opaque
  objects

• Capture local state deltas whenever possible

• Assign unique IDs to local states that repeat
  over
• different executions (IDs computed based on
  deltas)

Experimental Results
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y
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Acknowledgments This work was supported by NSF
CNS 0059379, SRC 2005-TJ-1318, and the Microsoft
HPC Institutes Program