Welcome!

Open Source Cloud Authors: Pat Romanski, Elizabeth White, Shelly Palmer, Karthick Viswanathan, Stackify Blog

Related Topics: Open Source Cloud, Java IoT, Industrial IoT, Microsoft Cloud, Machine Learning , Python

Open Source Cloud: Article

Python and gevent

Let’s talk about event loops

The easiest way to make your code run faster is to do less. At some point, though, you don’t want to do less. Maybe you want to do more, without it being any slower. Maybe you want to make what you have fast, without cutting out any of the work. What then? In this enlightened age, the answer is easy — parallelize it! Threads are always a good choice, but without careful consideration, it’s easy to create all manner of strange race conditions or out-of-order data access. So today, let’s talk about a different route: event loops.

Event whats?
If you’re not familiar with evented code, it’s a way to parallelize execution, similar to threading or multiprocessing. Unlike threads, though, evented code is typically cooperative — each execution path must voluntarily give up control. Each of these execution units actually runs in serial, and when finished, returns control to the main loop. The parallelization gain comes from cleverly dividing the work so that when they make a blocking call (i.e. a DB call, HTTP request, or disk access), they give up control, letting the main event loop run other functions and wait for the call to return. This is perfect for cases where you do a lot of I/O and relatively little work in the evented thread itself.

In my case, I’m interested in doing a number of heterogeneous, but related, data lookups in response to a web request. We’re running all of this behind our data access layer, which is an evented Thrift server. I have a number of functions (with a common API) I’m interested in running, and a naive implementation would look like this:

Python-Gevent-1

What does that do?

If we run this on a machine with TraceView installed, we’ll see the following request structure:

Pretty predictable. We called into each function serially, which is exactly what we said we’d do. We can also look at the raw events TraceView collected, and they tell a similar story:

All together now!

This seems like a good baseline, but let’s see what happens when we parallelize it. Let’s use Python’s gevent, which has two major selling points. First, it implements an event loop based on libevent, which means we won’t have to worry about actually implementing the event loop. We can just spawn separate greenlet (i.e., non-native) tasks, and gevent will handle all the scheduling. The other big advantage is that gevent knows about and can monkeypatch existing synchronous libraries to cede control when they block. This means that outside of the actual event spawning, we can leave our existing code untouched, and our external calls will just do the right thing.

That just leaves the questions of how to break up the work into parallel coroutines. It seems natural to give each of these functions their own, and then have our “main thread” wait for them all the finish. We do this by firing off each function in a separate task and collecting them in a list. We then wait for all of those tasks to finish and collect the results. Easy! Here’s what the same function as above looks like, but evented:

Python-Gevent-2

This calling change is all* that’s necessary to parallelize these functions! The next question is, did that help? Let’s look at the same graphs we had before, but now for the evented case:

Definitely different! Instead of running everything sequentially, we can see all seven functions running at the same time. As we’d hoped, this has a major impact on our total response time, as well. It’s 500ms faster — a speedup of 2x!

*Caveats
OK, so it’s not as perfectly simple as this example. There are a few “gotchas” that are worth bearing in mind when you start to use this in a real example.

This first one is that gevent mimics separate threads for each coroutine. This means that if you’re storing global state that’s thread-aware, gevent may discard it. Notably, Pylons/Pyramid uses thread-safe object proxies to store global request state, which means that new coroutines will hide that information from you. In our production version of this code, we explicitly pass that state from caller to callee, then set it in the global “pylons.request” object before running the function. It lets us seemlessly mix evented and non-evented functions, while only thinking about the details of gevent in one place.

The second big gotcha is error handling. Since these aren’t normal function calls, exceptions don’t propagate to the caller. They must be explicitly checked for on the task and re-thrown, if appropriate. This sort of error-case-checking is familiar to any C programmer, but it’s different than the normal Python idiom, so it’s worth thinking about.

Another caveat is that spawning multiple events doesn’t actually get you code-level parallelization. It runs blocking calls in parallel, but you still only get one interpreter thread to run your Python (no magic GIL sidestep here!). If you’re looking to speed up heavy computations or other CPU-intensive work, check out the multiprocessing module. Eventing really shines when the majority of your work is database calls, file access, or other blocking, out-of-process work.

Finally, if you’re looking to trace these kinds of calls with TraceView (like we did here), it’s pretty straightforward. The only thing to remember is to wrap your evented function calls using “oboe.log_method”, and pass “entry_kvs={‘Async’: True}”. The ensures that we calculate the timing information properly for all your parallel work.

But that’s it! You can use this technique to speed up existing projects, or build something an entirely new with gevent at the core. What are you planning on doing with it?

And, of course, if you want to instrument your evented project now, sign up for a 14-day trial of TraceView today!

Related Articles

More Stories By TR Jordan

A veteran of MIT’s Lincoln Labs, TR is a reformed physicist and full-stack hacker – for some limited definition of full stack. After a few years as Software Development Lead with Thermopylae Science and Techology, he left to join Tracelytics as its first engineer. Following Tracelytics merger with AppNeta, TR was tapped to run all of its developer and market evangelism efforts. TR still harbors a not-so-secret love for Matlab-esque graphs and half-baked statistics, as well as elegant and highly-performant code. Read more of his articles at www.appneta.com/blog or visit www.appneta.com.

@ThingsExpo Stories
SYS-CON Events announced today that Fusic will exhibit at the Japan External Trade Organization (JETRO) Pavilion at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Fusic Co. provides mocks as virtual IoT devices. You can customize mocks, and get any amount of data at any time in your test. For more information, visit https://fusic.co.jp/english/.
SYS-CON Events announced today that TMC has been named “Media Sponsor” of SYS-CON's 21st International Cloud Expo and Big Data at Cloud Expo, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Global buyers rely on TMC’s content-driven marketplaces to make purchase decisions and navigate markets. Learn how we can help you reach your marketing goals.
SYS-CON Events announced today that Enroute Lab will exhibit at the Japan External Trade Organization (JETRO) Pavilion at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Enroute Lab is an industrial design, research and development company of unmanned robotic vehicle system. For more information, please visit http://elab.co.jp/.
There is huge complexity in implementing a successful digital business that requires efficient on-premise and cloud back-end infrastructure, IT and Internet of Things (IoT) data, analytics, Machine Learning, Artificial Intelligence (AI) and Digital Applications. In the data center alone, there are physical and virtual infrastructures, multiple operating systems, multiple applications and new and emerging business and technological paradigms such as cloud computing and XaaS. And then there are pe...
SYS-CON Events announced today that Daiya Industry will exhibit at the Japan External Trade Organization (JETRO) Pavilion at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Daiya Industry specializes in orthotic support systems and assistive devices with pneumatic artificial muscles in order to contribute to an extended healthy life expectancy. For more information, please visit https://www.daiyak...
Real IoT production deployments running at scale are collecting sensor data from hundreds / thousands / millions of devices. The goal is to take business-critical actions on the real-time data and find insights from stored datasets. In his session at @ThingsExpo, John Walicki, Watson IoT Developer Advocate at IBM Cloud, will provide a fast-paced developer journey that follows the IoT sensor data from generation, to edge gateway, to edge analytics, to encryption, to the IBM Bluemix cloud, to Wa...
In his session at @ThingsExpo, Greg Gorman is the Director, IoT Developer Ecosystem, Watson IoT, will provide a short tutorial on Node-RED, a Node.js-based programming tool for wiring together hardware devices, APIs and online services in new and interesting ways. It provides a browser-based editor that makes it easy to wire together flows using a wide range of nodes in the palette that can be deployed to its runtime in a single-click. There is a large library of contributed nodes that help so...
With major technology companies and startups seriously embracing Cloud strategies, now is the perfect time to attend 21st Cloud Expo October 31 - November 2, 2017, at the Santa Clara Convention Center, CA, and June 12-14, 2018, at the Javits Center in New York City, NY, and learn what is going on, contribute to the discussions, and ensure that your enterprise is on the right path to Digital Transformation.
Agile has finally jumped the technology shark, expanding outside the software world. Enterprises are now increasingly adopting Agile practices across their organizations in order to successfully navigate the disruptive waters that threaten to drown them. In our quest for establishing change as a core competency in our organizations, this business-centric notion of Agile is an essential component of Agile Digital Transformation. In the years since the publication of the Agile Manifesto, the conn...
SYS-CON Events announced today that App2Cloud will exhibit at SYS-CON's 21st International Cloud Expo®, which will take place on Oct. 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. App2Cloud is an online Platform, specializing in migrating legacy applications to any Cloud Providers (AWS, Azure, Google Cloud).
WebRTC is great technology to build your own communication tools. It will be even more exciting experience it with advanced devices, such as a 360 Camera, 360 microphone, and a depth sensor camera. In his session at @ThingsExpo, Masashi Ganeko, a manager at INFOCOM Corporation, will introduce two experimental projects from his team and what they learned from them. "Shotoku Tamago" uses the robot audition software HARK to track speakers in 360 video of a remote party. "Virtual Teleport" uses a mu...
Internet of @ThingsExpo, taking place October 31 - November 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA, is co-located with 21st Cloud Expo and will feature technical sessions from a rock star conference faculty and the leading industry players in the world. The Internet of Things (IoT) is the most profound change in personal and enterprise IT since the creation of the Worldwide Web more than 20 years ago. All major researchers estimate there will be tens of billions devic...
Mobile device usage has increased exponentially during the past several years, as consumers rely on handhelds for everything from news and weather to banking and purchases. What can we expect in the next few years? The way in which we interact with our devices will fundamentally change, as businesses leverage Artificial Intelligence. We already see this taking shape as businesses leverage AI for cost savings and customer responsiveness. This trend will continue, as AI is used for more sophistica...
SYS-CON Events announced today that SourceForge has been named “Media Sponsor” of SYS-CON's 21st International Cloud Expo, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. SourceForge is the largest, most trusted destination for Open Source Software development, collaboration, discovery and download on the web serving over 32 million viewers, 150 million downloads and over 460,000 active development projects each and every month.
SYS-CON Events announced today that Massive Networks will exhibit at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Massive Networks mission is simple. To help your business operate seamlessly with fast, reliable, and secure internet and network solutions. Improve your customer's experience with outstanding connections to your cloud.
SYS-CON Events announced today that DXWorldExpo has been named “Global Sponsor” of SYS-CON's 21st International Cloud Expo, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Digital Transformation is the key issue driving the global enterprise IT business. Digital Transformation is most prominent among Global 2000 enterprises and government institutions.
SYS-CON Events announced today that WineSOFT will exhibit at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Based in Seoul and Irvine, WineSOFT is an innovative software house focusing on internet infrastructure solutions. The venture started as a bootstrap start-up in 2010 by focusing on making the internet faster and more powerful. WineSOFT’s knowledge is based on the expertise of TCP/IP, VPN, SS...
SYS-CON Events announced today that Akvelon will exhibit at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Akvelon is a business and technology consulting firm that specializes in applying cutting-edge technology to problems in fields as diverse as mobile technology, sports technology, finance, and healthcare.
SYS-CON Events announced today that TechTarget has been named “Media Sponsor” of SYS-CON's 21st International Cloud Expo, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. TechTarget storage websites are the best online information resource for news, tips and expert advice for the storage, backup and disaster recovery markets.
SYS-CON Events announced today that Dasher Technologies will exhibit at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 - Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Dasher Technologies, Inc. ® is a premier IT solution provider that delivers expert technical resources along with trusted account executives to architect and deliver complete IT solutions and services to help our clients execute their goals, plans and objectives. Since 1999, we've...