|By Jyoti Bansal||
|February 18, 2017 02:00 PM EST||
How Java's Built-In Garbage Collection Will Make Your Life Better (Most of the Time)
By Kirk Pepperdine
“No provision need be made for the user to program the return of registers to the free-storage list.”
This line (along with the dozen or so that followed it) is buried in the middle of John McCarthy’s landmark paper, “Recursive Functions of Symbolic Expressions and Their Computation by Machine,” published in 1960. It is the first known description of automated memory management.
In specifying how to manage memory in Lisp, McCarthy was able to exclude explicit memory management. Thus, McCarthy relieved developers of the tedium of manual memory management. What makes this story truly amazing is that these few words inspired others to incorporate some form of automated memory management—otherwise known as garbage collection (GC)—into more than three quarters of the more widely used languages and runtimes developed since then. This list includes the two most popular platforms, Java’s Virtual Machine (JVM) and .NET’s Common Language Runtime (CLR), as well as the up and coming Go Lang by Google. GC exists not just on big iron but on mobile platforms such as Android’s Dalvik, Android Runtime, and Apple’s Swift. You can even find GC running in your web browser as well as on hardware devices such as SSDs. Let’s explore some of the reasons why the industry prefers automated over manual memory management.
Automatic Memory Management’s Humble Beginnings
So, how did McCarthy devise automated memory management? First, the Lisp engine decomposed Lisp expressions into sub-expressions, and each S-expression was stored in a single word node in a linked list. The nodes were allocated from a free list, but they didn’t have to be returned to the free list until it was empty.
Once the free list was empty, the runtime traced through the linked list and marked all reachable nodes. Next, it scanned through the buffer containing all nodes, and returned unmarked nodes to the free list. With the free-list refilled, the application would continue on.
Today, this is known as a single-space, in-place, tracing garbage collection. The implementation was quite rudimentary: it only had to deal with an acyclic-directed graph where all nodes were exactly the same size. Only a single thread ran, and that thread either executed application code or the garbage collector. In contrast, today’s collectors in the JVM must cope with a directed graph with cycles and nodes that are not uniformly sized. The JVM is multi-threaded, running on multi-core CPUs, possibly multi-socketed motherboards. Consequently, today’s implementations are far more complex—to the point GC experts struggle to predict performance in any given situation.
Slow Going: Garbage Collection Pause Time
When the Lisp garbage collector ran, the application stalled. In the initial versions of Lisp it was common for the collector to take 30 to 40 percent of the CPU cycles. On 1960s hardware this could cause the application stall, in what is known as a stop-the-world pause, for several minutes. The benefit was that allocation had barely any impact on application throughput (the amount of useful work done). This implementation highlighted the constant battle between pause time and impact on application throughput that persists to this day.
In general, the better the pause time characteristic of the collector, the more impact it has on application throughput. The current implementations in Java all come with pause time/overhead costs. The parallel collections come with long pause times and low overheads, while the mostly concurrent collectors have shorter pause times and consume more computing resources (both memory and CPU).
The goal of any GC implementer is to maximize the minimum amount of processor time that mutator threads are guaranteed to receive, a concept known as minimum mutator utilization (MMU). Even so, current GC overheads can run well under 5 percent, versus the 15 to 20 percent overhead you will experience in a typical C++ application.
So why you don’t feel this overhead like you do in a Java application? Because the overhead is evenly spread throughout the C/C++ run time, it is perceptibly invisible to the end users. In fact the biggest complaint about managed memory is that it pauses your application at unpredictable times for an unpredictable amount of time.
Garbage Collection Advancements
Sun Java’s initial garbage collector did nothing to improve the image of garbage collection. Its single-threaded, single-spaced implementation stalled applications for long periods of time and created a significant drag on allocation rates. It wasn’t until Java 2, when a generational memory pool scheme—along with parallel, mostly concurrent and incremental collectors—was introduced. While these collectors offered improved pause time characteristics, pause times continue to be problematic. Moreover, these implementations are so complex that it’s unlikely most developers have the experience necessary to tune them. To further complicate the picture, IBM, Azul, and RedHat have one or more of their own garbage collectors—each with their own histories, advantages and quirks. In addition, a number of companies including SAP, Twitter, Google, Alibaba, and others have their own internal JVM teams with modified versions of the Garbage collectors.
Costs and Benefits of Modern-Day Garbage Collection
Over time, an addition of alternate and more complex allocation paths led to huge improvements in the allocation overhead picture. For example, a fast-path allocation in the JVM is now approximately 30 times faster than a typical allocation in C/C++. The complication: Only data that can pass an escape analysis test is eligible for fast-path allocation. (Fortunately the vast majority of our data passes this test and benefits from this alternate allocation path.)
Another advantage is in the reduced costs and simplified cost models that come with evacuating collectors. In this scheme, the collector copies live data to another memory pool. Thus, there is no cost to recover short-lived data. This isn’t an invitation to allocate ad nauseam, because there is a cost for each allocation and high allocation rates trigger more frequent GC activity and accumulate extra copy costs. While evacuating collectors helps make GC more efficient and predictable, there are still significant resource costs.
That leads us to memory. Memory management demands that you retain at least five times more memory than manual memory management needs. There are times the developer knows for certain that data should be freed. In those cases, it is cheaper to explicitly free rather than have a collector reason through the decision. It was these costs that originally caused Apple to choose manual memory management for Objective-C. In Swift, Apple chose to use reference counting. They added annotations for weak and owned references to help the collector cope with circular references.
There are other intangible or difficult-to-measure costs that can be attributed to design decisions in the runtime. For example, the loss of control over memory layouts can result in application performance being dominated by L2 cache misses and cache line densities. The performance hit in these cases can easily exceed a factor of 10:1. One of the challenges for future implementers is to allow for better control of memory layouts.
Looking back at how poorly GC performed when first introduced into Lisp and the long and often frustrating road to its current state, it’s hard to imagine why anyone building a runtime would want to use managed memory. But consider that if you manually manage memory, you need access to the underlying reference system—and that means the language needs added syntax to manipulate memory pointers.
Languages that rely on managed memory consistently lack the syntax needed to manage pointers because of the memory consistency guarantee. That guarantee states that all pointers will point where they should without dangling (null) pointers waiting to blow up the runtime, if you should happen to step on them. The runtime can’t make this guarantee if developers are allowed to directly create and manipulate pointers. As an added bonus, removing them from the language removes indirection, one of the more difficult concepts for developers to master. Quite often bugs are a result of a developer engaged in the mental gymnastics required to juggle a multitude of competing concerns and getting it wrong. If this mix contains reasoning through application logic, along with manual memory management and different memory access modes, bugs likely appear in the code. In fact, bugs in systems that rely on manual memory management are among the most serious and largest source of security holes in our systems today.
To prevent these types of bugs the developer always has to ask, “Do I still have a viable reference to this data that prevents me from freeing it?” Often the answer to this question is, “I don’t know.” If a reference to that data was passed to another component in the system, it’s almost impossible to know if memory can safely be freed. As we all know too well, pointer bugs will lead to data corruption or, in the best case, a SIGSEGV.
Removing pointers from the picture tends to yield a code that is more readable and easier to reason through and maintain. GC knows when it can reclaim memory. This attribute allows projects to safely consume third-party components, something that rarely happens in languages with manual memory management.
At its best, memory management can be described as a tedious bookkeeping task. If memory management can be crossed off the to-do list, then developers tend to be more productive and produce far fewer bugs. We have also seen that GC is not a panacea as it comes with its own set of problems. But thankfully the march toward better implementations continues.
Go Lang’s new collector uses a combination of reference counting and tracing to reduce overheads and minimize pause times. Azul claims to have solved the GC pause problem by driving pause times down dramatically. Oracle and IBM keep working on collectors that they claim are better suited for very large heaps that contain significant amounts of data. RedHat has entered the fray with Shenandoah, a collector that aims to completely eliminate pause times from the run time. Meanwhile, Twitter and Google continue to improve the existing collectors so they continue to be competitive to the newer collectors.
Share “How Java’s Built-In Garbage Collection Will Make Your Life Better (Most of the Time)” On Your Site
Cloud promises the agility required by today’s digital businesses. As organizations adopt cloud based infrastructures and services, their IT resources become increasingly dynamic and hybrid in nature. Managing these require modern IT operations and tools. In his session at 20th Cloud Expo, Raj Sundaram, Senior Principal Product Manager at CA Technologies, will discuss how to modernize your IT operations in order to proactively manage your hybrid cloud and IT environments. He will be sharing be...
Apr. 26, 2017 09:26 AM EDT Reads: 307
This recent research on cloud computing from the Register delves a little deeper than many of the "We're all adopting cloud!" surveys we've seen. They found that meaningful cloud adoption and the idea of the cloud-first enterprise are still not reality for many businesses. The Register's stats also show a more gradual cloud deployment trend over the past five years, not any sort of explosion. One important takeaway is that coherence across internal and external clouds is essential for IT right n...
Apr. 26, 2017 08:45 AM EDT Reads: 1,688
Enterprise architects are increasingly adopting multi-cloud strategies as they seek to utilize existing data center assets, leverage the advantages of cloud computing and avoid cloud vendor lock-in. This requires a globally aware traffic management strategy that can monitor infrastructure health across data centers and end-user experience globally, while responding to control changes and system specification at the speed of today’s DevOps teams. In his session at 20th Cloud Expo, Josh Gray, Chie...
Apr. 26, 2017 07:45 AM EDT Reads: 3,256
NHK, Japan Broadcasting, will feature the upcoming @ThingsExpo Silicon Valley in a special 'Internet of Things' and smart technology documentary that will be filmed on the expo floor between November 3 to 5, 2015, in Santa Clara. NHK is the sole public TV network in Japan equivalent to the BBC in the UK and the largest in Asia with many award-winning science and technology programs. Japanese TV is producing a documentary about IoT and Smart technology and will be covering @ThingsExpo Silicon Val...
Apr. 26, 2017 07:30 AM EDT Reads: 8,943
To more closely examine the variety of ways in which IT departments around the world are integrating cloud services, and the effect hybrid IT has had on their organizations and IT job roles, SolarWinds recently released the SolarWinds IT Trends Report 2017: Portrait of a Hybrid Organization. This annual study consists of survey-based research that explores significant trends, developments, and movements related to and directly affecting IT and IT professionals.
Apr. 26, 2017 04:30 AM EDT Reads: 1,674
Developers want to create better apps faster. Static clouds are giving way to scalable systems, with dynamic resource allocation and application monitoring. You won't hear that chant from users on any picket line, but helping developers to create better apps faster is the mission of Lee Atchison, principal cloud architect and advocate at New Relic Inc., based in San Francisco. His singular job is to understand and drive the industry in the areas of cloud architecture, microservices, scalability ...
Apr. 26, 2017 03:00 AM EDT Reads: 3,503
Today we can collect lots and lots of performance data. We build beautiful dashboards and even have fancy query languages to access and transform the data. Still performance data is a secret language only a couple of people understand. The more business becomes digital the more stakeholders are interested in this data including how it relates to business. Some of these people have never used a monitoring tool before. They have a question on their mind like “How is my application doing” but no id...
Apr. 25, 2017 10:30 PM EDT Reads: 7,174
Is your application too difficult to manage? Do changes take dozens of developers hundreds of hours to execute, and frequently result in downtime across all your site’s functions? It sounds like you have a monolith! A monolith is one of the three main software architectures that define most applications. Whether you’ve intentionally set out to create a monolith or not, it’s worth at least weighing the pros and cons of the different architectural approaches and deciding which one makes the most s...
Apr. 25, 2017 08:45 PM EDT Reads: 2,769
Cloud Expo, Inc. has announced today that Aruna Ravichandran, vice president of DevOps Product and Solutions Marketing at CA Technologies, has been named co-conference chair of DevOps at Cloud Expo 2017. The @DevOpsSummit at Cloud Expo New York will take place on June 6-8, 2017, at the Javits Center in New York City, New York, and @DevOpsSummit at Cloud Expo Silicon Valley will take place Oct. 31-Nov. 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA.
Apr. 25, 2017 08:30 PM EDT Reads: 2,565
In large enterprises, environment provisioning and server provisioning account for a significant portion of the operations team's time. This often leaves users frustrated while they wait for these services. For instance, server provisioning can take several days and sometimes even weeks. At the same time, digital transformation means the need for server and environment provisioning is constantly growing. Organizations are adopting agile methodologies and software teams are increasing the speed ...
Apr. 25, 2017 08:15 PM EDT Reads: 3,355
Back in February of 2017, Andrew Clay Schafer of Pivotal tweeted the following: “seriously tho, the whole software industry is stuck on deployment when we desperately need architecture and telemetry.” Intrigue in a 140 characters. For me, I hear Andrew saying, “we’re jumping to step 5 before we’ve successfully completed steps 1-4.”
Apr. 25, 2017 11:15 AM EDT Reads: 1,736
In his session at 20th Cloud Expo, Scott Davis, CTO of Embotics, will discuss how automation can provide the dynamic management required to cost-effectively deliver microservices and container solutions at scale. He will discuss how flexible automation is the key to effectively bridging and seamlessly coordinating both IT and developer needs for component orchestration across disparate clouds – an increasingly important requirement at today’s multi-cloud enterprise.
Apr. 25, 2017 06:00 AM EDT Reads: 4,335
Keeping pace with advancements in software delivery processes and tooling is taxing even for the most proficient organizations. Point tools, platforms, open source and the increasing adoption of private and public cloud services requires strong engineering rigor – all in the face of developer demands to use the tools of choice. As Agile has settled in as a mainstream practice, now DevOps has emerged as the next wave to improve software delivery speed and output. To make DevOps work, organization...
Apr. 25, 2017 03:15 AM EDT Reads: 8,894
In his general session at 19th Cloud Expo, Manish Dixit, VP of Product and Engineering at Dice, discussed how Dice leverages data insights and tools to help both tech professionals and recruiters better understand how skills relate to each other and which skills are in high demand using interactive visualizations and salary indicator tools to maximize earning potential. Manish Dixit is VP of Product and Engineering at Dice. As the leader of the Product, Engineering and Data Sciences team at D...
Apr. 25, 2017 03:00 AM EDT Reads: 5,929
Software as a service (SaaS), one of the earliest and most successful cloud services, has reached mainstream status. According to Cisco, by 2019 more than four-fifths (83 percent) of all data center traffic will be based in the cloud, up from 65 percent today. The majority of this traffic will be applications. Businesses of all sizes are adopting a variety of SaaS-based services – everything from collaboration tools to mission-critical commerce-oriented applications. The rise in SaaS usage has m...
Apr. 22, 2017 06:15 PM EDT Reads: 4,855
The proper isolation of resources is essential for multi-tenant environments. The traditional approach to isolate resources is, however, rather heavyweight. In his session at 18th Cloud Expo, Igor Drobiazko, co-founder of elastic.io, drew upon his own experience with operating a Docker container-based infrastructure on a large scale and present a lightweight solution for resource isolation using microservices. He also discussed the implementation of microservices in data and application integrat...
Apr. 22, 2017 05:45 AM EDT Reads: 6,210
We'd all like to fulfill that "find a job you love and you'll never work a day in your life" cliché. But in reality, every job (even if it's our dream job) comes with its downsides. For you, the constant fight against shadow IT might get on your last nerves. For your developer coworkers, infrastructure management is the roadblock that stands in the way of focusing on coding. As you watch more and more applications and processes move to the cloud, technology is coming to developers' rescue-most r...
Apr. 22, 2017 04:00 AM EDT Reads: 4,083
2016 has been an amazing year for Docker and the container industry. We had 3 major releases of Docker engine this year , and tremendous increase in usage. The community has been following along and contributing amazing Docker resources to help you learn and get hands-on experience. Here’s some of the top read and viewed content for the year. Of course releases are always really popular, particularly when they fit requests we had from the community.
Apr. 22, 2017 03:45 AM EDT Reads: 3,589
Even for the most seasoned IT pros, the cloud is complicated. It can be difficult just to wrap your head around the many terms and acronyms that make up the cloud dictionary-not to mention actually mastering the technology. Unfortunately, complicated cloud terms are often combined to the point that their meanings are lost in a sea of conflicting opinions. Two terms that are used interchangeably (but shouldn't be) are hybrid cloud and multicloud. If you want to be the cloud expert your company ne...
Apr. 21, 2017 04:15 PM EDT Reads: 2,232
SYS-CON Events announced today that CollabNet, a global leader in enterprise software development, release automation and DevOps solutions, will be a Bronze Sponsor of SYS-CON's 20th International Cloud Expo®, taking place from June 6-8, 2017, at the Javits Center in New York City, NY. CollabNet offers a broad range of solutions with the mission of helping modern organizations deliver quality software at speed. The company’s latest innovation, the DevOps Lifecycle Manager (DLM), supports Value S...
Apr. 18, 2017 03:30 PM EDT Reads: 4,439