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We present LeJit, a template-based framework for testing Java just-in-time (JIT) compilers. Like recent template-based frameworks, LeJit executes a template---a program with holes to be filled---to generate concrete programs given as inputs to Java JIT compilers. LeJit automatically generates template programs from existing Java code by converting expressions to holes, as well as generating necessary glue code (i.e., code that generates instances of non-primitive types) to make generated templates executable. We have successfully used LeJit to test a range of popular Java JIT compilers, revealing five bugs in HotSpot, nine bugs in OpenJ9, and one bug in GraalVM. All of these bugs have been confirmed by Oracle and IBM developers, and 11 of these bugs were previously unknown, including two CVEs (Common Vulnerabilities and Exposures). Our comparison with several existing approaches shows that LeJit is complementary to them and is a powerful technique for ensuring Java JIT compiler correctness. 

Abstract With the aid of high-resolution spatial and temporal observations from the Goode Solar Telescope, we present an investigation of the emergence, coalescence, and submergence of a moving magnetic feature (MMF) in the region surrounding a magnetic pore located at the periphery of a large sunspot. The results show that the MMF has a magnetic field strength greater than 500 G and is dominated by the horizontal magnetic component. We observe upflow at the inner part and downflow at the outer part, indicating a pattern of Evershed flow. The MMF emergence is accompanied by the expansion of a granule, which has several striations inside just like the twisted features found in the penumbra filament. Our analysis shows that although these striations have different properties of magnetic field and kinematics during the expansion of the granule, the overall magnetic and dynamic properties of the MMF remain stable. We find that the region where the MMF emerges and submerges becomes more penumbra-like, i.e., adjacent positive and negative values of elongated magnetic features that are parallel to each other, while the optical penumbra-like features are not apparent at the same time. Our work indicates that the dynamics of the MMF near the magnetic pore is important for the development of filamentary structure. The magnetic configuration produced by an MMF together with the elongation of a granule could thus be key to understand the formation of penumbra filaments. 

This paper analyses a model of strategic exploration in which competing players independently explore a set of alternatives. The model features a multiple-player multiple-armed bandit problem and captures a strategic trade-off between pre-emption—covert exploration of alternatives that the opponent will explore in the future—and prioritization—exploration of the most promising alternatives. Our results explain how the strategic trade-off shapes equilibrium behaviours and outcomes, for example, in technology races between superpowers and R&D competitions between firms. We show that players compete on the same set of alternatives, leading to duplicated exploration from start to finish, and they explore alternatives that are a priori less promising before more promising ones are exhausted. The model also predicts that competition induces players to implement unreliable technologies too early, even though they should wait for the technologies to mature. Coordinated exploration is impossible even if the alternatives are equally promising, but it can emerge in equilibrium following a phase of pre-emptive competition if there is a short deadline. With asymmetric capacities of exploration, the weak player conducts extensive instead of intensive exploration—exploring as many alternatives as the strong player does but never fully exploring any.