by | September 8, 2015 · 3:00 pm

What is a bug?

Buggy software doesn’t work. According to wikipedia: 

A software bug is an error … in a computer program or system that causes it to produce an incorrect or unexpected result, or to behave in unintended ways. Most bugs arise from mistakes and errors made by people in either a program’s source code or its design ...

When something is wrong with a program, we rarely hear of it having one bug — we hear of it having many bugs. I’m wondering: Where does one bug end and the next bug begin?

To answer this question, we need an operational definition of a bug, not the indirect notion present in the Wikipedia quote.[ref]Andreas Zeller, in his book Why Programs Fail, prefers the term defect to bug since the latter term is sometimes used to refer to erroneous behavior, rather than erroneous code. I stick with the term bug, in this post, and use it to mean the problematic code (only).[/ref]

This post starts to explore such a definition, but I’m not satisfied with it yet — I’m hoping you will provide your thoughts in the comments to move it forward.

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by | September 1, 2015 · 1:00 pm

PL conference papers to get a journal?

As I have written previously, academic computer science differs from other scientific disciplines in its heavy use of peer-reviewed conference publications.

Since other disciplines’ conferences typically do not employ peer review, results published at highly selective computer science conferences may not be given the credit they deserve, i.e., the same credit they would receive if published in a similarly selective journal.

The main remedy has simply been to explain the situation to the possibly confused party, be it a dean or provost or a colleague from another department. But this remedy is sometimes ineffective: At some institutions, scientists risk a poor evaluation if they publish too few journal articles, but they risk muting the influence of their work in their own community if they publish too few articles at top conferences.

The ACM publications board has recently put forth a proposal that takes this problem head on by formally recognizing conference publications as equal in quality to journal publications. How? By collecting them in a special journal series called the Proceedings of the ACM (PACM).

In this post I briefly summarize the motivation and substance of the ACM proposal and provide some thoughts about it. In the end, I support it, but with some caveats. You have the opportunity to voice your own opinion via survey. You can also read other opinions for (by Kathryn McKinley) and against (by David S. Rosenblum) the proposal (if you can get past the ACM paywall, but that’s a topic for another day…).

Update: PACM has been approved, as has a new journal series called PACM PL that will collect papers accepted by major SIGPLAN Conferences. It will debut during late 2017.

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by | June 9, 2015 · 11:00 am

Interview with Mozilla’s Aaron Turon

On the heels of Rust’s 1.0 release, we are pleased to be able to interview Mozilla’s Aaron Turon, a member of Rust’s core team (which is the leadership for the project that sets the overall direction). This is our third interview with a PL PhD working in industry.

Aaron Turon photo

Aaron Turon

What is your academic background?

I received my undergraduate degree at the University of Chicago, at a time where a lot of PL was happening (a lot of the folks who built or studied Standard ML were there); I did some research under John Reppy. After that, I went on to do a PhD at Northeastern University, which continues to have a thriving PL group; I was supervised by Mitchell Wand. Finally, I was a post-doc under Derek Dreyer at the Max Planck Institute for Software Systems (MPI-SWS).

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Filed under Interviews, PL in practice, Types

by | June 2, 2015 · 11:07 am

The PL Enthusiast Turns One!

Our first post to this blog appeared on June 2, 2014, so that makes today our one year anniversary!

Birthday candles

It’s the PL Enthusiast’s 1-year birthday

In celebration of the occasion, this post takes a look back over the last year as well as a brief look to what’s ahead.

We’d love your feedback about what you’ve seen so far, and what you’d like to see (or contribute!) next.

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by | May 27, 2015 · 2:00 pm

What is PL research and how is it useful?

If you are in the world of programming languages research, the announcement that UW had hired Ras Bodik away from Berkeley was big news. Quoting UW’s announcement:

Ras’s arrival creates a truly world-class programming languages group in UW CSE that crosses into systems, databases, security, architecture, and other areas. Ras joins recent hires Emina Torlak,[ref]We previously interviewed Emina on this blog.[/ref] Alvin Cheung, Xi Wang, and Zach Tatlock, and senior faculty members Dan Grossman and Mike Ernst.

And there’s also Luis Ceze, a regular publisher at PLDI, who ought to be considered as part of this group. With him, UW CSE has 8 out of 54 faculty with strong ties to PL. Hiring five PL-oriented faculty in three years, thus making PL a significant fraction of the faculty’s expertise, is (highly) atypical. What motivated UW CSE in its decision-making? I don’t know for sure, but I suspect they see that PL-oriented researchers are making huge inroads on important problems, bringing a useful perspective to unlock new results.

In this post, I argue why studying PL (for your PhD, Masters, or just for fun) can be interesting and rewarding, both because of what you will learn, and because of the increasing opportunities that are available, e.g., in terms of impactful research topics and funding for them.

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by | April 30, 2015 · 10:12 am

Ranking CS Departments by Publication Productivity, Interactively

Anyone familiar with American academia will tell you that the US News rankings of academic programs play an outsized role in this world. Among other things, US News ranks graduate programs of computer science, by their strength in the field at large as well as certain specialties. One of these specialties is Programming Languages, the focus of this blog.

The US News rankings are based solely on surveys. Department heads and directors of graduate studies at a couple of hundred universities are asked to assign numerical scores to graduate programs. Departments are ranked by the average score that they receive.

It’s easy to see that much can go wrong with such a methodology. A reputation-based ranking system is an election, and elections are meaningful only when their voters are well-informed. The worry here is that respondents are not necessarily qualified to rank programs in research areas that are not their own. Also, it is plausible that respondents would give higher scores to departments that have high overall prestige or that they are personally familiar with.

In this post, I propose using publication metrics as an input to a well-informed ranking process. Rather than propose a one-size-fits-all ranking, I provide a web application to allow users to compute their own rankings. This approach has limitations, which I discuss in detail, but I believe it’s a reasonable start to a better system.

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Filed under Process, Rankings, Research, Science

by | April 14, 2015 · 1:00 pm

Dynamic Software Updating: Linux 4.0 and Beyond

Last month,  of ZDNet alerted us that Linux 4.0 will provide support for “no-reboot patching.” The gist: When a security patch or other critical OS update comes out, you can apply it without rebooting.

While rebootless patching is convenient for everyone, it’s a game changer for some applications. For example, web and cloud hosting services normally require customers to experience some downtime while the OS infrastructure is upgraded; with rebootless patching, upgrades happen seamlessly. Or, imagine upgrades to systems hosting in-memory databases: Right now, you have to checkpoint the DB to stable storage, stop the system, upgrade it, restart it, read the data from stable storage, and restart service. Just the checkpointing and re-reading from disk could take tens of minutes. With rebootless patching, this disruption is avoided; cf. Facebook’s usage of a modified memcached that supports preserving state across updates.

I’m particularly excited by this announcement because I’ve been working on the general problem of updating running software, which I call dynamic software updating (DSU), for nearly 15 years. In this post, co-authored with my PhD student Luís Pina, I take a closer look at the challenge that DSU presents, showing that what Linux will support is still quite far from what we might hope for, but that ideas from the research community promise to get us closer to the ideal, both for operating systems and hopefully for many other applications as well.

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by | March 25, 2015 · 12:32 pm

Interview with Go’s Russ Cox and Sameer Ajmani

In this post I interview Russ Cox and Sameer Ajmani, who work at Google on the Go programming language. They share with me their path to working on the language, what they find unique and valuable about it, and plans for it going ahead.

This continues our series on PhDs in industry working on programming languages (Avik Chaudhuri was the first). Thanks to Russ and Sameer for taking the time to share their experiences!

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by | March 16, 2015 · 9:20 am

Teaching and Researching Programming Languages at a Liberal Arts College

During my tenure as a student and professor, I have been to many talks offering career advice to graduate students. Most of these talks focus on careers in research universities and industrial research labs, and leave out discussion of institutions, such as liberal arts colleges, that are primarily concerned with undergraduate education. This is unfortunate because many liberal arts colleges are highly selective institutions that offer exciting careers that mix research and teaching, albeit in a different way than careers in research universities.

One way to reduce the information deficit about liberal arts colleges is to report on the experiences of those who work at one. This is what we do in the present post. Specifically, I interview Steve Freund, who is a professor of computer science at Williams College, ranked by US News as the top liberal arts college in America. Steve is a highly successful PL researcher, known for his significant contributions to the analysis of concurrent programs. As a result, he is in a great position to give PL Enthusiast readers a view into what it’s like to be a teacher and researcher at a liberal arts institution. Continue reading →

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by | March 3, 2015 · 2:00 pm

What is noninterference, and how do we enforce it?

In this post I discuss a program security property called noninterference. I motivate why you might like it if your program satisfied noninterference, and show that the property is fundamental to many areas beyond just security. I also explore some programming languages and tools that might help you enforce noninterference, noting that while tainting analysis won’t get you the whole way there, research tools that attempt to do better have their own problems. I conclude with some suggestions for future research, in particular with the idea that testing noninterference may be a practical approach.

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