A Study of Concurrency Bugs and Advanced Development Support for Actor-based Programs

The actor model is an attractive foundation for developing concurrent applications because actors are isolated concurrent entities that communicate through asynchronous messages and do not share state. Thereby, they avoid concurrency bugs such as data races, but are not immune to concurrency bugs in general. This study taxonomizes concurrency bugs in actor-based programs reported in literature. Furthermore, it analyzes the bugs to identify the patterns causing them as well as their observable behavior. Based on this taxonomy, we further analyze the literature and find that current approaches to static analysis and testing focus on communication deadlocks and message protocol violations. However, they do not provide solutions to identify livelocks and behavioral deadlocks. The insights obtained in this study can be used to improve debugging support for actor-based programs with new debugging techniques to identify the root cause of complex concurrency bugs.Comment: - Submitted for review - Removed section 6 "Research Roadmap for Debuggers", its content was summarized in the Future Work section - Added references for section 1, section 3, section 4.3 and section 5.1 - Updated citation

Combination antiretroviral therapy and the risk of myocardial infarction RID C-2464-2008 RID B-4427-2008 RID H-3944-2011 RID B-5656-2009 RID E-7045-2010 RID A-1057-2008

Background: It remains controversial whether exposure to combination antiretroviral treatment increases the risk of myocardial infarction. Methods: In this prospective observational study, we enrolled 23,468 patients from 11 previously established cohorts from December 1999 to April 2001 and collected follow-up data until February 2002. Data were collected on infection with the human immunodeficiency virus and on risk factors for and the incidence of myocardial infarction. Relative rates were calculated with Poisson regression models. Combination antiretroviral therapy was defined as any combination regimen of antiretroviral drugs that included a protease inhibitor or a nonnucleoside reverse transcriptase inhibitor. Results: Over a period of 36,199 person-years, 126 patients had a myocardial infarction. The incidence of myocardial infarction increased with longer exposure to combination antiretroviral therapy (adjusted relative rate per year of exposure, 1.26 [95 percent confidence interval, 1.12 to 1.41]; P<0.001). Other factors significantly associated with myocardial infarction were older age, current or former smoking, previous cardiovascular disease, and male sex, but not a family history of coronary heart disease. A higher total serum cholesterol level, a higher triglyceride level, and the presence of diabetes were also associated with an increased incidence of myocardial infarction. Conclusions: Combination antiretroviral therapy was independently associated with a 26 percent relative increase in the rate of myocardial infarction per year of exposure during the first four to six years of use. However, the absolute risk of myocardial infarction was low and must be balanced against the marked benefits from antiretroviral treatment

Incidence of tuberculosis among HIV-infected patients receiving highly active antiretroviral therapy in Europe and North America

Background. We obtained estimates of the incidence of tuberculosis (TB) among patients receiving HAART and identified determinants of the incidence. Methods. We analyzed the incidence of TB during the first 3 years after initiation of HAART among 17,142 treatment-naive, AIDS- free persons starting HAART who were enrolled in 12 cohorts from Europe and North America. We used univariable and multivariable Poisson regression models to identify factors associated with the incidence. Results. During the first 3 years (36,906 person-years), 173 patients developed TB (incidence, 4.69 cases per 1000 person-years). In multivariable analysis, the incidence rate was lower for men who have sex with men, compared with injection drug users (relative rate, 2.46; 95% confidence interval [CI], 1.51-4.01), heterosexuals (relative rate, 2.42; 95% CI, 1.64-3.59), those with other suspected modes of transmission (relative rate, 1.66; 95% CI, 0.91-3.06), and those with a higher CD4(+) count at the time of HAART initiation (relative rate per log(2) cells/mL, 0.87; 95% CI, 0.84-0.91). During 28,846 person-years of follow-up after the first 6 months of HAART, 88 patients developed TB (incidence, 3.1 cases per 1000 person-years of follow-up). In multivariable analyses, a low baseline CD4(+) count (relative rate per log(2) cells/mL, 0.89; 95% CI, 0.83-0.96), 6-month CD4(+) count (relative rate per log(2) cells/mL, 0.90; 95% CI, 0.81-0.99), and a 6-month HIV RNA level 1400 copies/mL (relative rate, 2.21; 95% CI, 1.33-3.67) were significantly associated with the risk of acquiring TB after 6 months of HAART. Conclusion. The level of immunodeficiency at which HAART is initiated and the response to HAART are important determinants of the risk of TB. However, this risk remains appreciable even among those with a good response to HAART, suggesting that other interventions may be needed to control the TB epidemic in the HIV-infected population