Hans-Juergen Boehm

Hans-Juergen Boehm

Hans Boehm joined Google as a software engineer in the Android runtime group in 2014. Before that he held various positions at the University of Washington, Rice University, Xerox PARC, SGI (on the same campus as now), and most recently as research manager at HP Labs. He is an ACM Fellow.

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Authored Publications
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    Preview abstract The real numbers are pervasive, both in daily life, and in mathematics. Students spend much time studying their properties. Yet computers and programming languages generally provide only an approximation geared towards performance, at the expense of many of the nice properties we were taught in high school. Although this is entirely appropriate for many applications, particularly those that are sensitive to arithmetic performance in the usual sense, we argue that there are others, where it is a poor choice. If arithmetic computations and result are directly exposed to human users who are not floating point experts, floating point approximations tend to be viewed as bugs. For applications such as calculators, spreadsheets, and various verification tasks, the cost of precision sacrifices are high, and the performance benefit is often not critical. We argue that although previous attempts to provide accurate and understandable results for such applications using the recursive reals, were great steps in the right direction, they do not suffice. Comparing such numbers diverges if they are equal. But in many cases we cannot produce results expected by users without resolving equality of numbers. We propose an API for such a real number type, describe a detailed, and surprisingly compact and simple implementation, and demonstrate its utility. The approach relies heavily on classical number theory results. The resulting arithmetic, which takes advantage of these partial decision procedures, is used in a calculator application with more than 100 million users. View details
    Small-data computing: Correct calculator arithmetic
    Communications of the ACM (CACM Vol. 60 No. 8, August 2017), 60 (2017), pp. 44-49
    Preview abstract Calculators conventionally use some flavor of fixed precision floating point arithmetic. The bundled Android 6.0 Marshmallow calculator instead uses demand-drive evaluation or “constructive real” arithmetic to guarantee fully accurate results. We explain why this matters, the opportunities it creates, and the challenges in incorporating constructive real arithmetic in a tool aimed at a very broad audience. View details
    Makalu: Fast Recoverable Allocation of Non-volatile Memory
    Kumud Bhandari
    Dhruva R. Chakrabarti
    OOPSLA 2016, ACM, pp. 677-694 (to appear)
    Preview abstract Byte addressable non-volatile memory (NVRAM) is likely to supplement, and perhaps eventually replace, DRAM. Applications can then persist data structures directly in memory instead of serializing them and storing them onto a durable block device. However, failures during execution can leave data structures in NVRAM unreachable or corrupt. In this paper, we address memory management of non-volatile memory, offering an integrated allocator and garbage collector that maintains internal consistency, minimizes memory leaks, and is efficient in the face of failures. We show that a careful allocator design can both support a less restrictive and much more familiar programming model. By lazily persisting non-essential metadata and by employing a post-failure recovery-time garbage collector, the per allocation persistence overhead is greatly reduced. Experimental results show that the resulting online speed and scalability of our allocator are comparable to well-known transient allocators and significantly better than state-of-the-art persistent allocators. View details
    Outlawing ghosts: avoiding out-of-thin-air results
    Brian Demsky
    Workshop on Memory Systems Performance and Correctness (MSPC), ACM, New York, NY (2014)
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