05. – 10. November 2017, Dagstuhl Seminar 17451

New Challenges in Parallelism


Annette Bieniusa (TU Kaiserslautern, DE)
Hans-J. Boehm (Google – Palo Alto, US)
Maurice Herlihy (Brown University – Providence, US)
Erez Petrank (Technion – Haifa, IL)

Auskunft zu diesem Dagstuhl Seminar erteilt

Dagstuhl Service Team


Gemeinsame Dokumente
Programm des Dagstuhl Seminars [pdf]


A continuing goal of current multiprocessor software design is to improve the performance and reliability of parallel algorithms. Parallel programming has traditionally been attacked from widely different angles by different groups of people: Hardware designers designing instruction sets, programming language designers designing languages and library interfaces, and theoreticians developing models of parallel computation. Unsurprisingly, this has not always led to consistent results. Newly developing areas show every sign of leading to similar divergence. This Dagstuhl Seminar will bring together researchers and practitioners from all three areas to discuss and reconcile thoughts on these challenges.

Memory Models and Platforms

Fundamental questions about the semantics of shared memory remain. For example, it becomes increasingly clear that atomic accesses to variables without memory ordering guarantees, or with very weak ordering guarantees, are important in practice. It is surprisingly common to find data structures, such as simple counters, that effectively consist of a single machine word. These continue to be “supported” in languages like Java and C++, but there remains no generally accepted way of defining their semantics, and the specifications in these languages are clearly inadequate. Fundamental questions about memory models and concurrent data structures continue to be unresolved. Many Java concurrent data structures provide weaker than interleaving (”sequentially consistent”) semantics that can only be fully understood with a thorough understanding of the memory model. This fact seems to be neither widely appreciated nor discussed. Are the “acquire/release” semantics often used in practice sufficient? Could we afford the overhead of providing the programmer with a simpler model? The more theoretical side of our discipline often uses concepts, such as “safe” and “regular” registers that are quite foreign to the way in which parallel programming languages are actually defined. Are these notions reconcilable?

Non-Volatile Memory and Concurrency

Non-volatile memory (NVM) technologies are expected to support persistence in byte- addressable memory at densities higher than DRAM and at competitive speed. It is expected that NVM will unify the DRAM and SSD into a one-level storage system of persistent main memory with no need for a hard drive, and directly accessible from the programming language. Such a change in the platforms has a significant impact on the design of software and in particular on concurrent algorithms. One implication is that standard functionalities need to be written for a single-tier memory rather then the standard two-tier paradigm. The design of widely available applications, such as database systems, assume that two-tier memory levels are present, and optimizations are based on the fact that these two memory levels have very different behaviors. Concurrency needs to be re-thought in the presence of the new memory structure. Another implication is that software is now expected to deal with persistence. This has strong connections to thread synchronization issues, but has not been traditionally studied with concurrent algorithms. Addressing these challenges is crucial for building systems on non-volatile memories and we would like to explore potential solutions in the Seminar.

  Creative Commons BY 3.0 DE
  Annette Bieniusa, Hans-J. Boehm, Maurice Herlihy, and Erez Petrank

Dagstuhl Seminar Series


  • Data Structures / Algorithms / Complexity
  • Hardware
  • Programming Languages / Compiler


  • Concurrent programming
  • Parallel programming


Bücher der Teilnehmer 

Buchausstellung im Erdgeschoss der Bibliothek

(nur in der Veranstaltungswoche).


In der Reihe Dagstuhl Reports werden alle Dagstuhl-Seminare und Dagstuhl-Perspektiven-Workshops dokumentiert. Die Organisatoren stellen zusammen mit dem Collector des Seminars einen Bericht zusammen, der die Beiträge der Autoren zusammenfasst und um eine Zusammenfassung ergänzt.


Download Übersichtsflyer (PDF).


Es besteht weiterhin die Möglichkeit, eine umfassende Kollektion begutachteter Arbeiten in der Reihe Dagstuhl Follow-Ups zu publizieren.

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