Defining and Verifying Durable Opacity: Correctness for Persistent Software Transactional Memory

Non-volatile memory (NVM), aka persistent memory, is a new paradigm for memory that preserves its contents even after power loss. The expected ubiquity of NVM has stimulated interest in the design of novel concepts ensuring correctness of concurrent programming abstractions in the face of persistency. So far, this has lead to the design of a number of persistent concurrent data structures, built to satisfy an associated notion of correctness: durable linearizability. In this paper, we transfer the principle of durable concurrent correctness to the area of software transactional memory (STM). Software transactional memory algorithms allow for concurrent access to shared state. Like linearizability for concurrent data structures, opacity is the established notion of correctness for STMs. First, we provide a novel definition of durable opacity extending opacity to handle crashes and recovery in the context of NVM. Second, we develop a durably opaque version of an existing STM algorithm, namely the Transactional Mutex Lock (TML). Third, we design a proof technique for durable opacity based on refinement between TML and an operational characterisation of durable opacity by adapting the TMS2 specification. Finally, we apply this proof technique to show that the durable version of TML is indeed durably opaque. The correctness proof is mechanized within Isabelle.Comment: This is the full version of the paper that is to appear in FORTE 2020 (https://www.discotec.org/2020/forte

Dermatopathology in sub-Saharan Africa: a systematic 5-year analysis of all histopathological diagnoses from the Regional Dermatology Training Centre (RDTC) in Moshi, Tanzania.

BACKGROUND Proper diagnosis of skin diseases relies on dermatopathology, the most important diagnostic technique in dermatology. Unfortunately, there are few dermatopathology institutions in sub-Saharan Africa, where little is known about the spectrum of histopathological features observed. OBJECTIVES To investigate the spectrum of dermatopathological diagnoses made in a sub-Saharan African reference centre of a large, mainly rural area. PATIENTS/METHODS To retrospectively evaluate all dermatopathological diagnoses made over a period of 5 years at the Regional Dermatology Training Centre (RDTC) in Moshi, Tanzania. RESULTS There were a total of 1554 skin biopsy specimens. In 45% of cases, there were inflammatory diseases, most frequently lichenoid conditions. Cutaneous neoplasms represented 30.4% of all diagnoses, with Kaposi's sarcoma (KS) and, less frequently, squamous cell carcinoma (SCC) being the two most common neoplastic conditions. The latter also reflected the intensive management of persons with albinism in the RDTC. The distribution of histological diagnoses seemed to correlate with the overall clinical spectrum of cutaneous diseases managed in the RDTC. CONCLUSIONS In this African study inflammatory conditions are the main burden of skin diseases leading to a diagnostic biopsy. Our findings provide further evidence that KS, primarily related to the high prevalence of HIV infection is an epidemiological problem. Both SCC and basal cell carcinoma represent another relatively common malignant cutaneous neoplasms, reflecting the presence of specific populations at risk. The challenging spectrum of histological diagnoses observed in this specific African setting with basic working conditions shows that development of laboratory services of good standards and specific training in dermatopathology are urgently needed

Defining and verifying durable opacity: correctness for persistent software transactional memory

Non-volatile memory (NVM), aka persistent memory, is a new paradigm for memory that preserves its contents even after power loss. The expected ubiquity of NVM has stimulated interest in the design of novel concepts ensuring correctness of concurrent programming abstractions in the face of persistency. So far, this has lead to the design of a number of persistent concurrent data structures, built to satisfy an associated notion of correctness: durable linearizability. In this paper, we transfer the principle of durable concurrent correctness to the area of software transactional memory (STM). Software transactional memory algorithms allow for concurrent access to shared state. Like linearizability for concurrent data structures, opacity is the established notion of correctness for STMs. First, we provide a novel definition of durable opacity extending opacity to handle crashes and recovery in the context of NVM. Second, we develop a durably opaque version of an existing STM algorithm, namely the Transactional Mutex Lock (TML). Third, we design a proof technique for durable opacity based on refinement between TML and an operational characterisation of durable opacity by adapting the TMS2 specification. Finally, we apply this proof technique to show that the durable version of TML is indeed durably opaque. The correctness proof is mechanized within Isabelle