ZeroMQ: Messaging for Many Applications PDF
Preview ZeroMQ: Messaging for Many Applications
ZeroMQ Pieter Hintjens Beijing • Cambridge • Farnham • Köln • Sebastopol • Tokyo Download from Wow! eBook To Noémie, Freeman, and Gregor. Special Upgrade Offer If you purchased this ebook directly from oreilly.com, you have the following benefits: DRM-free ebooks—use your ebooks across devices without restrictions or limitations Multiple formats—use on your laptop, tablet, or phone Lifetime access, with free updates Dropbox syncing—your files, anywhere If you purchased this ebook from another retailer, you can upgrade your ebook to take advantage of all these benefits for just $4.99. Click here to access your ebook upgrade. Please note that upgrade offers are not available from sample content. Preface ØMQ in a Hundred Words ØMQ (also known as ZeroMQ, 0MQ, or zmq) looks like an embeddable networking library, but acts like a concurrency framework. It gives you sockets that carry atomic messages across various transports, like in-process, inter- process, TCP, and multicast. You can connect sockets N-to-N with patterns like fan-out, pub-sub, task distribution, and request-reply. It’s fast enough to be the fabric for clustered products. Its asynchronous I/O model gives you scalable multicore applications, built as asynchronous message-processing tasks. It has a score of language APIs and runs on most operating systems. ØMQ is from iMatix and is LGPLv3 open source. The Zen of Zero The Ø in ØMQ is all about trade-offs. On the one hand, this strange name lowers ØMQ’s visibility on Google and Twitter. On the other hand, it annoys the heck out of some Danish folk who write us things like “ØMG røtfl”, and “Ø is not a funny-looking zero!” and “Rødgrød med Fløde!” (which is apparently an insult that means “May your neighbours be the direct descendants of Grendel!”). Seems like a fair trade. Originally, the zero in ØMQ was meant to signify “zero broker” and (as close to) “zero latency” (as possible). Since then, it has come to encompass different goals: zero administration, zero cost, zero waste. More generally, “zero” refers to the culture of minimalism that permeates the project. We add power by removing complexity rather than by exposing new functionality. How This Book Came to Be In the summer of 2010, ØMQ was still a little-known niche library described by its rather terse reference manual and a living but sparse wiki. Martin Sustrik and I were sitting in the bar of the Hotel Kyjev in Bratislava plotting how to make ØMQ more widely popular. Martin had written most of the ØMQ code, and I’d put up the funding and organized the community. Over some Zlatý Bažant, we agreed that ØMQ needed a new, simpler website and a basic guide for new users. Martin collected some ideas for topics to explain. I’d never written a line of ØMQ code before this, so it became a live learning documentary. As I worked through simple examples to more complex ones, I tried to answer many of the questions I’d seen on the mailing list. Because I’d been building large-scale architectures for 30 years, there were a lot of problems I was keen to throw ØMQ at. Amazingly, the results were mostly simple and elegant, even when working in C. I felt a pure joy learning ØMQ and using it to solve real problems, which brought me back to programming after a few years’ pause. And often, not knowing how it was “supposed” to be done, we improved ØMQ as we went along. From the start, I wanted the guide to be a community project, so I put it onto GitHub and let others contribute with pull requests. This was considered a radical, even vulgar approach by some. We came to a division of labor: I’d do the writing and make the original C examples, and others would help fix the text and translate the examples into other languages. This worked better than I dared hope. You can now find all the examples in several languages, and many in a dozen languages. It’s a kind of programming language Rosetta Stone, and a valuable outcome in itself. We set up a high score: reach 80% translation and your language gets its own guide. PHP, Python, Lua, and Haxe reached this goal. People asked for PDFs, and we created those. People asked for ebooks, and got those. About a hundred people have contributed to the guide to date. The guide achieved its goal of popularizing ØMQ. The style pleases most and annoys some, which is how it should be. In December 2010, my work on ØMQ and the guide stopped, as I found myself going through late-stage cancer, heavy surgery, and six months of chemotherapy. When I picked up work again in mid- 2011, it was to start using ØMQ in anger for one of the largest use-cases imagineable: on the mobile phones and tablets of the world’s biggest electronics company. But the goal of the guide was, from the start, a printed book. So it was exciting to get an email from Bill Lubanovic in January 2012, introducing me to his editor, Andy Oram, at O’Reilly, suggesting a ØMQ book. “Of course!” I said. Where do I sign? How much do I have to pay? Oh, I get money for this? All I have to do is finish it?” Of course, as soon as O’Reilly announced a ØMQ book, other publishers started sending out emails to potential authors. You’ll probably see a rash of ØMQ books coming out next year. That’s good. Our niche library has hit the mainstream and deserves its six inches of shelf space. My apologies to the other ØMQ authors. We’ve set the bar horribly high, and my advice is to make your books complementary. Perhaps focus on a specific language, platform, or pattern. This is the magic and power of communities: be the first community in a space, stay healthy, and you own that space for ever. Audience This book is written for professional programmers who want to learn how to make the massively distributed software that will dominate the future of computing. We assume you can read C code, because most of the examples here are in C (even though ØMQ is used in many languages). We assume you care about scale, because ØMQ solves that problem above all others. We assume you need the best possible results with the least possible cost, because otherwise you won’t appreciate the trade-offs that ØMQ makes. Other than that basic background, we try to present all the concepts in networking and distributed computing you will need to use ØMQ.
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