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Making software reliable is one of the most important technological challenges facing our society today. This thesis presents a new type system that addresses this problem by statically preventing several important classes of programming errors. If a program type checks, we guarantee at compile time that the program does not contain any of those errors. We designed our type system in the context of a Java-like object-oriented language; we call the resulting system SafeJava. The SafeJava type system offers significant software engineering benefits. Specifically, it provides a statically enforceable way of specifying object encapsulation and enables local reasoning about program correctness; it combines effects clauses with encapsulation to enable modular checking of methods in the presence of subtyping; it statically prevents data races and deadlocks in multithreaded programs, which are known to be some of the most difficult programming errors to detect, reproduce, and

Multithreaded programs are notoriously prone to race conditions. Prior work on dynamic race detectors includes fast but imprecise race detectors that report false alarms, as well as slow but precise race detectors that never report false alarms. The latter typically use expensive vector clock operations that require time linear in the number of program threads. This paper exploits the insight that the full generality of vector clocks is unnecessary in most cases. That is, we can replace heavyweight vector clocks with an adaptive lightweight representation that, for almost all operations of the target program, requires only constant space and supports constant-time operations. This representation change significantly improves time and space performance, with no loss in precision. Experimental results on Java benchmarks including the Eclipse development environment show that our FASTTRACK race detector is an order of magnitude faster than a traditional vector-clock race detector, and roughly twice as fast as the high-performance DJIT + algorithm. FASTTRACK is even comparable in speed to ERASER on our Java benchmarks, while never reporting false alarms.

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Abstract. The race condition checker rccjava uses a formal type system to statically identify potential race conditions in concurrent Java programs, but it requires programmer-supplied type annotations. This paper describes a type inference algorithm for rccjava. Due to the interaction of parameterized classes and dependent types, this type inference problem is NP-complete. This complexity result motivates our new approach to type inference, which is via reduction to propositional satisfiability. This paper describes our type inference algorithm and its performance on programs of up to 30,000 lines of code. 1

Atomicity is a fundamental correctness property in multithreaded programs, both because atomic code blocks are amenable to sequential reasoning (which significantly simplifies correctness arguments), and because atomicity violations often reveal defects in a program’s synchronization structure. Unfortunately, all atomicity analyses developed to date are incomplete in that they may yield false alarms on correctly synchronized programs, which limits their usefulness. We present the first dynamic analysis for atomicity that is both sound and complete. The analysis reasons about the exact dependencies between operations in the observed trace of the target program, and it reports error messages if and only if the observed trace is not conflict-serializable. Despite this significant increase in precision, the performance and coverage of our analysis is competitive with earlier incomplete dynamic analyses for atomicity.

Atomicity is a fundamental correctness property in multithreaded programs. This paper presents an algorithm for verifying atomicity via type inference. The underlying type system supports guarded, write-guarded, and unguarded fields, as well as thread-local data, parameterized classes and methods, and protected locks. We describe an implementation of this algorithm for Java and discuss its performance and usability on benchmarks totaling sixty thousand lines of code.

Concurrent programs are notorious for containing errors that are difficult to reproduce and diagnose. Two common kinds of concurrency errors are data races and atomicity violations (informally, atomicity means that executing methods concurrently is equivalent to executing them serially). Several static and dynamic (run-time) analysis techniques exist to detect potential races and atomicity violations. Run-time checking may miss errors in unexecuted code and incurs significant run-time overhead. On the other hand, run-time checking generally produces fewer false alarms than static analysis; this is a significant practical advantage, since diagnosing all of the warnings from static analysis of large codebases may be prohibitively expensive. This paper explores the use of static analysis to significantly decrease the overhead of run-time checking. Our approach is based on a type system for analyzing data races and atomicity. A type discovery algorithm is used to obtain types for as much of the program as possible (complete type inference for this type system is NP-hard, and parts of the program might be untypable). Warnings from the typechecker are used to identify parts of the program from which run-time checking can safely be omitted. The approach is completely automatic, scalable to very large programs, and significantly reduces the overhead of run-time checking for data races and atomicity violations.

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Abstract. Concurrent programs are notorious for containing errors that are difficult to reproduce and diagnose. A common kind of concurrency error is deadlock, which occurs when a set of threads is blocked each trying to acquire a lock held by another thread in that set. Static and dynamic (run-time) analysis techniques exist to detect deadlocks. Havelund’s GoodLock algorithm detects potential deadlocks at runtime. However, it detects only potential deadlocks involving exactly two threads. This paper presents a generalized version of the GoodLock algorithm that detects potential deadlocks involving any number of threads. Run-time checking may miss errors in unexecuted code. On the positive side, run-time checking generally produces fewer false alarms than static analysis. This paper explores the use of static analysis to automatically reduce the overhead of run-time checking. We extend our type system, Extended Parameterized Atomic Java (EPAJ), which ensures absence of races and atomicity violations, with Boyapati et al.’s deadlock types. We give an algorithm that infers deadlock types for a given program and an algorithm that determines, based on the result of type inference, which run-time checks can safely be omitted. The new type system, called Deadlock-Free EPAJ (DEPAJ), has the added benefit of giving stronger atomicity guarantees than previous atomicity type systems. 1