A true hardware read barrier

We describe a technique for storage allocation and garbage collection in the absence of significant co‐operation from the code using the allocator. This limits garbage collection overhead to the time actually required for garbage collection. In particular, application programs that rarely or never make use of the collector no longer encounter a substantial performance penalty. This approach greatly simplifies the implementation of languages supporting garbage collection. It further allows conventional compilers to be used with a garbage collector, either as the primary means of storage reclamation, or as a debugging tool.Our approach has two potential disadvantages. First, some garbage may fail to be reclaimed. Secondly, we use a ‘stop and collect’ approach, thus making the strategy unsuitable for applications with severe real‐time constraints. We argue that the first problem is, to some extent, inherent in any garbage collection system. Furthermore, based on our experience, it is usually not significant in practice. In spite of the second problem, we have had favourable experiences with interactive applications, including some that use a heap of several megabytes.

AbstractjHISC is an object-oriented processor for embedded system aiming at accelerating Java execution by hardware approach. Garbage collection is one of the critical tasks in a Java Virtual Machine. In this paper, we have conduct a study of dynamic object allocation and garbage collection behavior of Java program based on SPECjvm 98 benchmark suite and MIDP applications for mobile phones. Life, size, and reference count distribution of Java objects are measured. We found most Java objects die very young, small in size and have small number reference counts. Reference counting object cache with hardware write barrier and object allocator is proposed to provide the hardware concurrent garbage collection for small size objects in jHISC. Hardware support on write barrier greatly reduces the overhead to perform the reference count update. The reference counting collector reclaims the memory occupied by object immediately after the object become garbage. The hardware allocator provides a constant time object allocation. From the investigation, over half of Java objects can be garbage collected by the object cache that makes it unnecessary for these objects to copy to the main memory.KeywordsGarbage CollectionCache LineBenchmark SuiteJava Virtual MachineGarbage CollectorThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Obesity and cardiorespiratory fitness exhibit negative and positive impacts, respectively, on executive function. Nevertheless, the combined effects of these two factors on executive function remain unclear. This study investigated the combined effects of obesity and cardiorespiratory fitness on response inhibition of executive function from both behavioral and neuroelectric perspectives. Ninety-six young adults aged between 18 and 25 years were recruited and assigned into four groups: the high cardiorespiratory fitness with normal weight (NH), high cardiorespiratory fitness with obesity (OH), low cardiorespiratory fitness with normal weight (NL), and low cardiorespiratory fitness with obesity (OL) groups. The stop-signal task and its induced P3 component of event-related potentials was utilized to index response inhibition. The participants with higher cardiorespiratory fitness (i.e., the NH and OH groups) demonstrated better behavioral performance (i.e., shorter response times and higher accuracy levels), as well as shorter stop-signal response times and larger P3 amplitudes than their counterparts with low cardiorespiratory fitness (i.e., the NL and OL groups). The study provides first-hand evidence of the substantial effects of cardiorespiratory fitness on the response inhibition, including evidence that the detrimental effects of obesity might be overcome by high cardiorespiratory fitness.

Solid State Drives (SSDs) have replaced magnetic disks in many application areas, as they provide very high performance for arbitrary access patterns. Nevertheless, data written to a physical page has to be erased before a page can be rewritten. The corresponding garbage collection (GC) process can only be performed on a block granularity, where a block includes many pages, impacting both the performance and lifetime of an SSD. The cost of a GC process is typically measured in terms of its write amplification, i.e., the number of blocks internally written by the SSD divided by the number of write requests of the host.Several GC heuristics have been proposed to optimize the write amplification of SSDs. These heuristics have been mostly empirically evaluated, while no thorough theoretical results are available on the optimality of GC algorithms even for seemingly simple cases like uniform and independent access distributions.In this work, we theoretically investigate the GREEDY GC strategy for uniformly independently distributed write accesses. We therefore model the garbage collection process on SSDs as a stochastic process and prove that the expected write amplification incurred by the GREEDY GC strategy is at most that of any other online GC strategy.

Determination of the Post-Failure Behavior of Brittle Rock Using a Servo-Controlled Testing Machine. The use of the servo-controlled testing machine to control fracture when a rock specimen is deformed beyond its peak strength is discussed. This region of deformation can not usually be examined because excess energy released by the loading system produces rapid disintegration of the specimen. In the test method described the energy release is controlled by a high frequency electronic servo-control system acting in combination with a hydraulic system of very short response time. The control causes the excess energy to be withdrawn before it can be released into the disintegrating specimen, by removing pressurized fluid from the hydraulic system. Theoretical considerations reveal that the condition for controlled fracture is determined by the ability of the hydraulic loading system to unload rapidly. This may be expressed in terms of a ‘dynamic stiffness’,K r , of the hydraulic system. For sufficiently small deformation rates and short servo-control response times the fracture process can be controlled, even though the unloading slope of the stress-strain curve of the rock specimen tends to become infinitely steep. The experimental technique is described in detail and some results obtained in studying the post-failure behavior of Tennessee Marble under uni-axial and bi-axial compression using the new system are presented.

The aim of this paper was to examine the roles of working memory, single-step mental addition skills, and strategy use in multi-step mental addition in two independent samples of Chinese elementary students through different approaches to manipulate two dimensions of task characteristics (the primary task). In Study 1, we manipulated strategy types through the dimension of schema automaticity (whether intermediate sums were 10s) and the dimension of working memory load (WML, two steps versus four steps). A hierarchical linear model (HLM) analysis was conducted at case level, strategy level, and individual level. In Study 2, we manipulated task characteristics through schema automaticity (one-time versus two-time regrouping) and the WML (partial versus complete decomposition). A three-level HLM analysis was applied. The general findings of Study 1 and Study 2 suggested that shorter response time on single-step mental addition corresponded to shorter response time on multi-step mental addition. The use of strategies (from easier to more difficult strategies) negatively predicted response time on multi-step mental addition. Easier strategy was associated with shorter response time on multi-step mental addition. Better phonological loop was associated with shorter response time on multi-step mental addition. The findings in both studies highlighted the important role of phonological loop in mental addition in Chinese children, suggesting that the involvement of a specific subcomponent of working memory in mental arithmetic might be subject to linguistic, instructional, and contextual factors.

The Bloom Program, which began as a demonstration project, is an ongoing community pharmacy-based mental illness and addictions program funded by the government of Nova Scotia. To be eligible to offer the Bloom Program, interested pharmacists were required to complete a 9-part application on behalf of their pharmacies. A process evaluation was conducted to inform future program implementation changes of program components, including the application process. Qualitative interviews from 24 pharmacists were inductively analyzed to determine the challenges and opportunities in the program's application process. Key and impactful components of the application process included training, providing a mental health and addictions resource centre within the pharmacy and completing outreach activities with local mental health and addictions services and support organizations. The training content and format for the program was highly valued. Community outreach to local mental health and addictions resources, and other health care resources in the community, was particularly valuable in supporting patient navigation of the health care system and extending the pharmacists' networks. Components of the application process were challenging for many pharmacists but were beneficial personally and professionally. Dedicated resources (e.g., time and staffing) are required for the efficient completion of the application process. Pharmacists viewed the Bloom Program application process as intensive yet necessary and relevant for preparing to deliver the Program. The demonstration project process evaluation was essential for elucidating the strengths of the application process and, importantly, identifying areas for improvement. Can Pharm J (Ott) 2021;154:xx-xx.

Page protection is often used to achieve memory access monitoring in many applications, dealing with program-analysis, checkpoint-based failure recovery, and garbage collection in managed runtime systems. Typically, low overhead access monitoring is limited by the relatively large page-level granularity of memory management unit hardware support for virtual memory protection. In this paper, we improve upon traditional page-level mechanisms by additionally using hardware support for virtualization in order to achieve fine and flexible granularities that can be smaller than a page. We first introduce a memory allocator based on page protection that can achieve fine-grained monitoring. Second, we explain how virtualization hardware support can be used to achieve dynamic adjustment of the monitoring granularity. In all, we propose a process-level virtual machine to achieve dynamic and fine-grained monitoring. Any application can run on our process-level virtual machine without modification. Experimental results for an incremental checkpoint tool provide a use-case to demonstrate our work. Comparing with traditional page-based checkpoint, our work can effectively reduce the amount of checkpoint data and improve performance.

Android operating system has a function, called LowMemoryKiller, which forcibly terminates application processes when size of available memory is less than the threshold. On reusing the same application again, re-creation of a process is required and takes longer time. ART (Android Runtime environment) has several GC (Garbage Collection) implementations, and choice of GC has effect on size of processes and behavior of LowMemoryKiller. In this paper, we investigate performance of GC implementations and propose a method for choosing GC implementation depending on application size and state. Then, we show our experimental results and demonstrate that our method reduces the number of process terminations cause by LowMemoryKiller.

More and more embedded systems are emerging based on managed language runtime systems using garbage collected languages such as Java, Python, or the .NET language family. Furthermore, the garbage collection (GC) process is a bottleneck in an embedded system, effectively blocking most other processes including mutator memory access, responding to inputs, or asserting outputs. We demonstrate a valuable new heap memory architecture for garbage collected embedded systems, which works by creating a direct path between memory modules to achieve a two-fold speedup for a memory copy operation as compared to a baseline scenario using multiplexed shared address- and databusses. This direct-path memory setup is generalisable, and memory modules will continue to work as expected when not engaged in garbage collection. The solution space is evaluated by simulating GC activity extracted from the Elephant Track GC tracer. One particular solution is also implemented in hardware to demonstrate the practical realisation of the direct fast copy architecture.

With the advent of new flash-based memory technologies with ultra-low latency, directly applying inline data deduplication in flash-based storage devices can degrade the system performance since key deduplication operations lie on the shortened critical write path of such devices. To address the problem, we propose a Content-Aware Garbage Collection scheme (CAGC), which embeds the data deduplication into the data movement workflow of the Garbage Collection (GC) process in ultra-low latency flash-based SSDs. By parallelizing the operations of valid data pages migration, hash computing and flash block erase, the deduplication-induced performance overhead is alleviated and redundant page writes during the GC period are eliminated. To further reduce data writes and write amplification during GC, CAGC separates and stores data pages in different regions based on their reference counts. The performance evaluation of our CAGC prototype implemented in FlashSim shows that CAGC significantly reduces the number of flash blocks erased and data pages migrated during GC, leading to improved user I/O performance and reliability of ultra-low latency flash-based SSDs.

In order to prepare new types of ferroelectric liquid crystals (FLC) with a large spontaneous polarization and a short response time toward electric field, optically active compounds possessing a fluorinated asymmetric frame were synthesized utilizing optically active 2-fluoroalkanols prepared from R- (+) -1, 2-epoxyalkanes, or 1, 1, 1-trifluoro-2-octanol and 3-trifluoromethylalkanoic acids prepared by the optical resolution of their racemates. The liquid crystals prepared from the above mentioned fluorinated compounds exhibited such remarkable FLC characteristics as a wide temperature range of the S*c phase, a large spontaneous polarization, and a short response time. We now wish to describe the synthetic procedures and the mesomorphic properties of these new types of FLC.

Progressive online aggregation in a distributed stream system

Effective seed-assisted synthesis of gold nanoparticles anchored nitrogen-doped graphene for electrochemical detection of glucose and dopamine

A novel acidic pH fluorescent probe based on a benzothiazole derivative