Lua Garbage Collection Tutorial – Complete Guide

In the realm of game development, an often underrated yet highly critical aspect is understanding and optimizing memory management. In the context of Lua, a popular and easy to learn scripting language widely used in game development platforms such as Roblox, this concept ushers in through the mechanism of garbage collection. With our easy-to-follow guide on Lua garbage collection, we’ll delve into what it means, why it’s essential to learn, and how it can be effectively demonstrated with simple examples, keeping it beneficial for both budding and seasoned coders.

What is Lua Garbage Collection?

Garbage collection in Lua is a form of automatic memory management. It identifies and frees up ‘garbage,’ or memory segments that are no longer required by the program, enabling efficient memory utilization.

Why Should You Learn About It?

Knowledge of Lua garbage collection is a powerhouse skill under your belt as a game developer. The scripting environment only has a finite amount of memory; failure in proper management can lead to your game running poorly or even crashing. Understanding Lua garbage collection helps optimize your game’s performance and delivers a seamless gaming experience which is a crucial factor in determining the success of a game.

What is it Used for?

Lua uses garbage collection to manage memory automatically. While the programmer focuses on crafting the game’s mechanics, Lua’s garbage collector works behind the scenes, ensuring that unneeded memory space is freed and available for future use. It plays a vital part in preventing memory leaks – a common bane in game development.

There you have it. In this tutorial, we are going to understand Lua’s garbage collection through interactive coding sessions and also look forward to learning how to manage memory more efficiently in your game development journey. Buckle up and let’s start scripting!

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Getting Started with Lua Garbage Collection

In Lua, one of the critical functions for managing garbage collection is collectgarbage(). This function calls the garbage collector to perform different tasks. Let’s understand with examples how to use this.

Our first interaction with memory management in Lua comes in the form of the collectgarbage("count") function, which returns the current memory used by Lua (in Kbytes).


After executing this simple script, the output is the memory allocated by Lua till that point of execution (in Kbytes).

Performing a Full Garbage-Collection Cycle

The next important thing to understand is how to trigger garbage collection manually. The function collectgarbage("collect") can be used to start a full garbage-collection cycle.

print("Memory Before:", collectgarbage("count"))
myTable = nil -- remove the reference to the table
collectgarbage("collect") -- force a garbage collection cycle
print("Memory After:", collectgarbage("count"))

In the above script, we first print the current memory used by Lua. Then we free up some memory by setting a table variable to nil, and then call collectgarbage("collect") to start a full garbage-collection cycle. Finally, we print the memory used by Lua. The “Memory After” value should be less than the “Memory Before” value, showing that some memory was freed after garbage collection.

Garbage Collection Control

Lua also allows you to control garbage collection to some extent. This can be extremely helpful when you want to optimize your game or application’s performance. The collectgarbage("setpause") and collectgarbage("setstepmul") functions allow you to set the garbage collector’s aggressiveness.

collectgarbage("setpause", 110)    -- Make the collector wait a little longer before starting a new cycle
collectgarbage("setstepmul", 500)  -- Make the collector run faster when it does run

The setpause function takes a percentage as its argument, which specifies the ratio of memory allocation to memory freed by the collector, at which it will start a new cycle. The default value is 200, which means the collector will start a new cycle when the total memory in use is twice the memory freed in the last cycle.

The setstepmul function also takes a percentage as its argument, which specifies the speed of the collector relative to memory allocation. The default value is 200, meaning the collector will run twice as fast as memory is allocated.

Learning these functions and how they affect garbage collection in Lua can give you fine control over your application’s memory management, leading to better optimization and smoother performance.

Further Exploring Lua’s Garbage Collection

In addition to the basics of invoking and controlling Lua’s garbage collector, there are a few additional aspects you can explore to fine-tune memory management.

Garbage Collection Status

While control is critical, monitoring the garbage collector status is equally crucial to manage and diagnose memory usage in Lua. You can use the function collectgarbage("isrunning") for checking if the garbage collector is running:

print("Is Garbage Collector Running: ", collectgarbage("isrunning"))

The output of the above script will be a boolean value indicating whether the garbage collector is running (true) or not (false).

Stopping and Restarting Garbage Collection

You can stop the garbage collector using the collectgarbage("stop") function. You might want to stop the garbage collector in some rare cases, such as during a critical game event to avoid performance hiccups.

print("Is Garbage Collector Running: ", collectgarbage("isrunning"))

Manually restarting the garbage collector can be just as important, and this requires the collectgarbage("restart") function.

print("Is Garbage Collector Running: ", collectgarbage("isrunning"))

In the scripts above, we first stopped the garbage collector and then restarted it, confirming the action by checking the status of the garbage collector each time.

Understanding “step”

The garbage collection cycle in Lua is divided into incremental steps. It means the garbage collector will only do part of its work before stopping. You can perform a single step of garbage collection using collectgarbage("step").

print("Memory after step: ", collectgarbage("count"))

In this example, we called a single step of garbage collection and then printed the memory used by Lua. If there was any garbage, this usage would be reduced somewhat.

Setting the Garbage Collector’s Threshold

Lastly, you can set a limit for garbage generation before the collector starts a new cycle. For this, use the collectgarbage("setmemlimit") function.

collectgarbage("setmemlimit", 1024) -- set limit to 1MB

In this example, we set the threshold to 1024 Kbytes. Once this limit is reached, the garbage collector will start a new cycle.

By understanding and utilizing these functionalities, you can manage memory more efficiently and take full advantage of Lua’s automatic garbage collection mechanism. It becomes particularly vital in the sphere of game development, where liveliness and user experience are paramount.

Dive Deeper into Lua Garbage Collection

Let’s now explore more aspects of Lua’s garbage collection mechanism.

Counting the Steps

In some scenarios, you may want to know how many steps the collector has taken. For this, use the collectgarbage("stepcount") function.

print("Step count: ", collectgarbage("stepcount"))

This script prints the number of steps taken by the garbage collector since it was last started or reset.

Drastic Measures: Lua Garbage Stoppers

In extreme cases, you might need to halt the garbage collector explicitly. For this, use the collectgarbage("stop") function:

print("Is the garbage collector running? ", collectgarbage("isrunning"))

This script stops the garbage collector and confirms it by checking if it is running.

After you’ve stopped the garbage collector, you can restart it using the collectgarbage("restart") function:

print("Is the garbage collector running? ", collectgarbage("isrunning"))

This code will restart the garbage collector and confirm it by checking if it is running.

Prudent Actions: Return and Reclaim

If you want to know how much memory the most recent garbage collection cycle reclaimed, you can use the collectgarbage("getlastmajorcyclecost") function.

print("Cost of the last major cycle: ", collectgarbage("getlastmajorcyclecost"))

The above script prints the cost of the last major garbage collection cycle. The cost is measured in the number of bytes of memory that were freed.

When you want to get the estimated cost of the next major garbage collection cycle, use collectgarbage("getestimate"):

print("Estimated cost of the next major cycle: ", collectgarbage("getestimate"))

This script will provide you with an estimated cost in bytes for the next major garbage collection cycle.

Lua’s garbage collection system is a powerful tool that allows you to manage your programs’ memory usage efficiently. By taking control of the garbage collection cycle and utilizing the functions provided by the Lua language, you can create games that are optimized and run smoothly. By understanding how Lua handles memory, using its built-in functions to control and monitor garbage collection, you can make sure your games are always running at their best!

Next Steps in Your Lua and Game Development Journey

Having grasped the fundamental aspects of Lua garbage collection, you’re steadily steering your way towards becoming a proficient game developer. Remember, mastering game development consists of a blend of theory and abundant practice. Thus, it’s time to apply your newfound skills to practical projects.

At Zenva, we cover everything from the basics to advanced game development. Our Roblox Game Development Mini-Degree is a valuable resource ensemble designed to elevate your game development skills. Offered as a comprehensive program, it spans multiple aspects of game creation using Roblox Studio and Lua.

Whether you’re a novice or a seasoned developer, our mini-degree provides an enriching learning experience. The Roblox platform, with over 160 million users monthly, offers a diverse and vast playground to implement your skills.

Being a project-oriented program, you get hands-on with the practical aspects of game development, sharpening your skills through real challenges. There is also the exciting reward of earning a certificate upon completion to validate your competencies.

For an all-encompassing exploration of our Roblox courses, do visit our Roblox Course Collection. Whichever your proficiency level might be, sustained learning and practice is the key to mastering game development. So keep exploring, keep learning, and let’s start creating some amazing games!


Understanding and effectively leveraging Lua’s garbage collection is a key stepping stone in your journey towards becoming a skilled game developer. By mastering this fundamental aspect, you are strengthening the backbone of your games, ensuring they run smoothly and effectively.

Ready to embark on your coding crusades and create unparalleled gaming experiences? Dive into our comprehensive Roblox Game Development Mini-Degree to amplify your skills and take your game development journey to new heights with Zenva. Happy coding!

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