What are Memory Leaks, and How Can You Fix Them?

Just as the brain is crucial to human life, memory is equally important for computers. Your system can’t take on tasks when it doesn’t possess enough RAM.

RAM shortage and some other memory issues can occur due to memory leaks. Hence, we will show how you can detect memory leaks and fix them.

But before that, let’s understand more about memory leaks and why should you fix them.

What are Memory Leaks?

Imagine a parking lot right next to a shopping mall, where all the cars are parked, whether or not the shoppers have finished their shopping. Over time, there won’t be any space left for new vehicles to park, leading to traffic blocks and reducing the overall mall’s efficiency.

The same is the case with computers too!

Computer applications, similar to cars in a parking lot, may forget to free up the used memory when no longer required. This puts a load on your memory and leaves no space for new tasks to run smoothly, resulting in a common memory error called memory leak.

An example code to showcase memory leak:

void memory_allocation() {
    int *ptr = (int*)malloc(sizeof(int));
}

The C code snippet above allocates some memory for an integer variable and assigns its memory location to the pointer ‘ptr’. But there is no code written to deallocate the memory, which leads to memory leaks.

def infinite_rec():
    return infinite_rec()

In the above Python code, there is no base case to terminate the function. So, the above code results in stack overflow and memory leaks.

Common Causes For Memory Leaks

Programmer Negligence

The first reason for a memory leak is the negligence of the programmer.

Programmers often allocate data to memory but sometimes forget to release it when no longer needed. At some point, this keeps the entire memory busy and provides no room for upcoming tasks, leading to what we call a ‘memory leak’ error.

Programmer Languages

Using programming languages with no built-in memory management system can cause memory leaks.

Programming languages like Java have built-in garbage collectors to automatically take care of memory management.

But, for example, C doesn’t have a built-in garbage collector. You, the programmer, should manually handle the memory here, leading to memory leaks whenever you forget to clean up the memory manually.

Heavy Cache Usage

Frequently used tasks, data, or applications are cached for faster access.

This can lead to a memory leak error if the items are cached but not cleared, though they are outdated or no longer align with your current usage patterns.

Global Variables Usage

Global variables hold the allocated data throughout the application’s lifetime. So, the usage of more global variables uses a lot of memory for a longer time and causes memory leaks.

Inefficient Data Structures

Developers often create their own data structures to accomplish custom functionalities. However, memory leak errors show up when these data structures can’t deallocate the used memory.

Unclosed Connections

Not closing files, databases, network connections, etc., after usage can also lead to memory leak errors.

Consequences of Memory Leaks

Low Performance – You will see a gradual decrease in your application’s or system’s performance as memory leaks accumulate. This is because there will be no memory available for tasks to complete, slowing down your application.

Crashed Apps – Applications run out of memory as memory leaks grow. At some point, with no memory available, the program crashes, resulting in data loss and application failure.

Security Vulnerabilities – Not properly clearing sensitive data like passwords, personal details, or confidential information from memory after usage exposes this data to attackers during memory leaks. 

Resource Exhaustion – Applications take up more space from your RAM when they run out of memory due to memory leaks. This increases the resource consumption and reduces the overall system performance.

How to Detect Memory Leaks?

Manual Code Inspection

Examine your source code to find instances where the memory is allocated but not cleared after usage. Look for variables and objects in the code that are using memory but not releasing it when no longer needed.

Also, keep an eye on the major sources of data storage, i.e., ensure data structures manage the allocated memory well.

Static Code Analysis

Various well-designed static analysis tools analyze your compiler source code and detect memory leak cases.

Sometimes, they track common patterns, rules, and errors in your code to guess memory leaks ahead, even before they occur.

Dynamic Analysis Tools

These tools use the dynamic approach to analyze the code during execution and detect memory leaks.

Dynamic analysis tools examine the run time behavior of objects, functions, and their memory usage. This is why these tools are highly accurate in detecting memory leaks.

Profiling Tools

Profiling tools give you insights into how the application is using the memory.

You, as a developer, can use this info to analyze the program’s memory usage and optimize the memory management techniques to prevent application crashes and memory degradation issues.

Memory Leak Detection Libraries

Some programming languages offer in-built or third-party libraries to detect memory leaks in your program.

For example, Java has a garbage collector to deal with memory, and C offers CrtDbg for memory management.

Also, specialized libraries like LeakCanary, Valgrind, YourKit, etc., address memory leaks in different types of applications.

How to Fix Memory Leak?

Identify Memory Leaks

To fix memory leaks, you first need to identify them.

You can either do a manual inspection or use some automated tool to detect whether the app is leaking memory. You may try the other memory leak detection methods mentioned above to spot the leaks.

Identify Objects Causing the Leak

Once you confirm the app is leaking memory in the above step, you should look for the objects and data structures causing the leak. Understand how they are allocated memory and where they are supposed to release the memory.

Create Test Cases

Now you narrowed down the exact spot of memory leak. So, create a test case to make sure that you have correctly identified the source of the memory leak and to confirm the leak gets away once you fix those specific objects.

Fix the Code

Add the memory deallocation code to release the blocked memory by the identified faulty objects. If the code already exists, update the code to ensure it properly deallocates the used memory.

Test Again

Again, use leak detection tools or automated tests to check if the application performs as intended and if there is no memory blockage.

Also, test the performance and functionalities of your application to ensure that the code update doesn’t affect other factors of the app.

Best Practices to Prevent Memory Leaks

Be a Responsible Programmer

You should be conscious of deallocating the used memory or releasing the memory pointers while writing the code itself. This will minimize memory leak issues.

Remember the below code? As mentioned at the beginning of the article, there is no memory deallocation code snippet, so it leads to a memory leak.

void memory_allocation() {
    int *ptr = (int*)malloc(sizeof(int));
}

Here is how you, as a programmer, can deallocate the memory.

delete ptr;

Use Equipped Programming Languages

Programming languages such as Java or Python employ built-in memory management libraries like garbage collectors to automatically handle memory leaks.

Though you overlook a few cases, these built-in tools handle them, preventing potential memory leaks.

Hence, I recommend you use such programming languages where memory management comes built-in.

Circular References

Avoid circular references in your program.

Circular references follow a closed loop of objects referring to each other. For example, object a refers to b, object b refers to c, and object c again refers to a, with no end in the loop. So, circular references lead to an infinite loop, causing memory leaks.

Minimize the usage of global variables

You should avoid using global variables if you are concerned about your memory efficiency. Global variables use up your memory throughout the application runtime, which is a bad practice in memory management.

So, switch to local variables. These are memory efficient as they release the memory once the function call is done.

Global variables look the following, but only use them when necessary.

int x = 5 // Global variable
void func(){
    print(x)
}

But use local variables as follows:

void func(){
    int x = 5 // Local variable
    print(x)
}

Limit Cache Memory

Set a limit to the memory that the cache can use. Sometimes, all the tasks you do in the system will be pushed to the cache memory, and this accumulated cache storage leads to memory leaks.

So, limiting the cache can prevent memory leaks from occurring.

Test well

Include memory leak tests in your testing phase.

Create automated tests and cover all the edge cases to detect memory leaks before releasing the code to production.

Equip Monitoring Tools

Use automatic profiling tools to monitor your memory usage. Tracking your memory usage regularly helps you identify potential leaks and fix them ahead of time.

Visual Studio profiler, NET Memory profiler, and JProfiler are a few good tools in this context.

Conclusion

Efficient memory management is necessary to achieve the application’s peak performance, and memory leaks can’t be ignored in this context. For effective memory management, you should handle memory leaks and prevent them from occurring in the future. This article is all about how you can do this.

We showed you various methods to detect memory leaks, proven steps to fix them, and practices you can follow to avoid future memory leaks.

Next, you may also explore how to fix “out of memory” Error in Windows within 5 minutes.