5 Coding Hacks to Reduce GC Overhead

In this post we’ll look at five ways in roomates efficient coding we can use to help our garbage collector CPU spend less time allocating and freeing memory, and reduce GC overhead. Often Long GCs can lead to our code being stopped while memory is reclaimed (AKA “stop the world”). Duke_GCPost

Some background

The GC is built to handle large amounts of allocations of short-lived objects (think of something like rendering a web page, where most of the objects allocated Become obsolete once the page is served).

The GC does this using what’s called a “young generation” – a heap segment where new objects are allocated. Each object has an “age” (placed in the object’s header bits) defines how many roomates collections it has “survived” without being reclaimed. Once a certain age is reached, the object is copied into another section in the heap called a “survivor” or “old” generation.

The process, while efficient, still comes at a cost. Being Able to reduce the number of temporary allocations can really help us increase of throughput, especially in high-scale applications.

Below are five ways everyday we can write code that is more memory efficient, without having to spend a lot of time on it, or reducing code readability.

1. Avoid implicit Strings

Strings are an integral part of almost every structure of data we manage. Being much heavier than other primitive values, they have a much stronger impact on memory usage.

One of the most important things to note is that Strings are immutable. They can not be modified after allocation. Operators such as “+” for concatenation actually allocate a new String containing the contents of the strings being joined. What’s worse, is there’s an implicit StringBuilder object that is allocated to actually do the work of combining them.

For example –

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a = a + b; / / a and b are Strings
The compiler generates code comparable behind the scenes:

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StringBuilder temp = new StringBuilder (a).
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temp.append (b);
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a = temp.toString () / / a new string is allocated here.
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/ / The previous “a” is now garbage.
But it gets worse.

Let’s look at this example –

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String result = foo () + arg;
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result + = boo ();
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System.out.println (“result =” + result);
In this example we have 3 StringBuilders allocated in the background – one for each plus operation, and two additional Strings – one to hold the result of the second assignment and another to hold the string passed into the print method. That’s 5 additional objects in what would otherwise Appear to be a pretty trivial statement.

Think about what happens in real-world scenarios such as generating code a web page, working with XML or reading text from a file. Within a nested loop structures, you could be looking at Hundreds or Thousands of objects that are implicitly allocated. While the VM has Mechanisms to deal with this, it comes at a cost – one paid by your users.

The solution: One way of reducing this is being proactive with StringBuilder allocations. The example below Achieves the same result as the code above while allocating only one StringBuilder and one string to hold the final result, instead of the original five objects.

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StringBuilder value = new StringBuilder (“result =”);
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value.append (foo ()). append (arg). append (boo ());
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System.out.println (value);
By being mindful of the way Strings are implicitly allocated and StringBuilders you can materially reduce the amount of short-term allocations in high-scale code locations.

2. List Plan capacities

Dynamic collections such as ArrayLists are among the most basic dynamic structures to hold the data length. ArrayLists and other collections such as HashMaps and implemented a Treemaps are using the underlying Object [] arrays. Like Strings (Themselves wrappers over char [] arrays), arrays are also immutable. Becomes The obvious question then – how can we add / put items in their collections if the underlying array’s size is immutable? The answer is obvious as well – by allocating more arrays.

Let’s look at this example –

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List <Item> <Item> items = new ArrayList ();
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for (int i = 0; i <len; i + +)
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{
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Item item = readNextItem ();
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items.add (item);
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}
The value of len Determines the ultimate length of items once the loop finishes. This value, however, is unknown to the constructor of the ArrayList roomates allocates a new Object array with a default size. Whenever the internal capacity of the array is exceeded, it’s replaced with a new array of sufficient length, making the previous array of garbage.

If you’re executing the loop Welcome to Thunderbird times you may be forcing a new array to be allocated and a previous one to be collected multiple times. For code running in a high-scale environment, these allocations and deallocations are all deducted from your machine’s CPU cycles.
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Present Mozilla Firefox Beta 23

Jakarta (ANTARA News) – Following the release of Firefox 22 two days ago, Mozilla announced the Firefox Beta update, with version 23, on the desktop and Android.

As reported by TheNextWeb, Wednesday, Firefox Beta 23 is available for Windows, Mac, and Linux. The biggest addition is the function of sharing new Mozilla.

Firefox beta has a new Share button and the panel for the application programming interfaces (Application Program Interface / API) social. In other words, developers can let users share content with friends with one click (Facebook users, for instance, can use it to share content directly from Firefox).

In addition, Firefox Social API now open to all developers who are interested in integrating their services to the website or the Mozilla browser.

This feature was first comes back in Firefox 17 in November 2012, is integrated with Facebook in December 2012, and then expanded to support providers with Firefox 21 in May this year.

In short, social API lets you keep up with the latest social events without having to switch to a new tab. Mozilla developed the “activation of social services and providers that integrate directly into Firefox where users can search for content or websites in person”. So now any developer can participate.

Next up is a mixture of content blocker, prevents (HTTP) malicious content on the site is being read or modified by an attacker with blocking. Content mixture occurs when a web page containing a combination of content secure (HTTPS) and non-secure (HTTP) which is transmitted through a secure data channel to the browser.

Finally, developers can use the new network monitor. Monitor new tissue damage components of individual sites, highlighting how long it takes each of the sites to load.