Efficient, deterministic and deadlock-free concurrency

High Performance …, 2010

The advent of multicore processors has made concurrent programming languages mandatory. However, most concurrent programming models come with two major pitfalls: non-determinism and deadlocks. By determinism, we mean the output behavior of the program is independent of the scheduling choices (e.g., the operating system) and depends only on the input behavior. A few concurrent programming models provide deterministic behavior by providing constructs that impose additional synchronization, but the improper (or the out of order) use of these constructs leads to problems like deadlocks.

2009

Describing parallel hardware and software is difficult, especially in an embedded setting. Five years ago, we started the shim project to address this challenge by developing a programming language for hardware/software systems. The resulting language describes asynchronously running processes that has the useful property of scheduling-independence: the i/o of a shim program is not affected by any scheduling choices.

… and Models for Co-Design, 2008 …, 2008

Concurrent programming languages are becoming mandatory with the advent of multi-core processors. Two major concerns in any concurrent program are data races and deadlocks. Each are potentially subtle bugs that can be caused by non-deterministic scheduling choices in most concurrent formalisms. As an alternative, the SHIM concurrent language guarantees the absence of data races by eschewing shared memory, but a SHIM program may still deadlock if a program violates a communication protocol.

2006

Concurrent programming languages should be a good fit for embedded systems because they match the intrinsic parallelism of their architectures and environments. Unfortunately, most concurrent programming formalisms are prone to races and nondeterminism, despite the presence of mechanisms such as monitors.

Parallel & Distributed Processing …, 2010

Multicore shared-memory architectures are becoming prevalent but bring many programming challenges. Among the biggest is non-determinism: the output of the program does not depend merely on the input, but also on scheduling choices taken by the operating system.

We present an e cient algorithm for \precisely" determining the possible alternate orderings of events from a program trace for a class of synchronization operations. The class includes, post and wait without clear, a restricted form of semaphores, and message passing where the sender names the receiver. The ordering information is precise in that a race detection system could be built using the ordering information such that if the program does not contain any data races for a given input, no races will be reported, and if the the program does contain data races, at least one of those races will be reported.

Lecture Notes in Computer Science, 2018

Synchronous Programming (SP) is a universal computational principle that provides deterministic concurrency. The same input sequence with the same timing always results in the same externally observable output sequence, even if the internal behaviour generates uncertainty in the scheduling of concurrent memory accesses. Consequently, SP languages have always been strongly founded on mathematical semantics that support formal program analysis. So far, however, communication has been constrained to a set of primitive clock-synchronised shared memory (csm) data types, such as data-flow registers, streams and signals with restricted read and write accesses that limit modularity and behavioural abstractions. This paper proposes an extension to the SP theory which retains the advantages of deterministic concurrency, but allows communication to occur at higher levels of abstraction than currently supported by SP data types. Our approach is as follows. To avoid data races, each csm type publishes a policy interface for specifying the admissibility and precedence of its access methods. Each instance of the csm type has to be policy-coherent, meaning it must behave deterministically under its own policy-a natural requirement if the goal is to build deterministic systems that use these types. In a policy-constructive system, all access methods can be scheduled in a policy-conformant way for all the types without deadlocking. In this paper, we show that a policy-constructive program exhibits deterministic concurrency in the sense that all policyconformant interleavings produce the same input-output behaviour. Policies are conservative and support the csm types existing in current SP languages. Technically, we introduce a kernel SP language that uses arbitrary policy-driven csm types. A big-step fixed-point semantics for this language is developed for which we prove determinism and termination of constructive programs.

2016

Writing concurrent programs is a hard task, even when using high-level synchronization primitives such as transactional memories together with a functional language with well-controlled side-effects such as Haskell, because the interferences generated by the processes to each other can occur at dif-ferent levels and in a very subtle way. The problem occurs when a thread leaves or exposes the shared data in an inconsistent state with respect to the application logic or the real meaning of the data. In this paper, we propose to associate contracts to transactions and we define a program transformation that makes it possible to extend static contract checking in the context of STM Haskell. As a result, we are able to check statically that each transaction of a STM Haskell program handles the shared data in a such way that a given consistency property, expressed in the form of a user-defined boolean function, is preserved. This ensures that bad interference will not occur during the exe...

2006

In this paper, we present a new algorithm for detecting data-races in an execution of a concurrent program. Our algorithm is sound and precise, that is, it reports a race in an execution iff there are two accesses to a shared variable along the execution that are not ordered by the happens-before relation. Previous algorithms for computing the happens-before relation are based on clock vectors. On the other hand, our algorithm is based solely on the concept of locksets and is able to capture all mutual-exclusion synchronization idioms uniformly with one mechanism. Our lockset algorithm could be very useful for improving the precision of flow-sensitive static analyses, particularly those for detecting data-races and atomicity violations in concurrent programs. We present one such analysis, a model checking algorithm that uses our lockset algorithm both to check for races exhaustively and perform partial-order reduction when races are absent. Our characterization of the happens-before relation in terms of locksets rather than clock vectors is crucial for the fixpoint computation inherent in model checking and other flow-sensitive analyses. We have implemented our algorithm and used it to prove the absence of data-races and assertion failures on a number of examples containing a variety of synchronization idioms.