Lazy Initialization

Lazy Initialization for Performance in Go¶

In Go, some resources are expensive to initialize, or simply unnecessary unless certain code paths are triggered. That’s where lazy initialization becomes useful: it defers the construction of a value until the moment it’s actually needed. This pattern can improve performance, reduce startup overhead, and avoid unnecessary work—especially in high-concurrency applications.

Why Lazy Initialization Matters¶

Initializing complex resources—such as database connections, caches, or large data structures—at application startup can significantly delay launch time and unnecessarily consume memory. Lazy initialization ensures these resources are only created when needed, optimizing resource usage and performance.

Additionally, lazy initialization is crucial when you have code that might be executed multiple times, but you need a resource or logic executed precisely once. This pattern helps ensure idempotency and avoids redundant processing.

Using `sync.Once` for Thread-Safe Initialization¶

Go provides the sync.Once type to easily implement lazy initialization that is safe for concurrent use:

var (
    resource *MyResource
    once     sync.Once
)

func getResource() *MyResource {
    once.Do(func() {
        resource = expensiveInit()
    })
    return resource
}

In this example, expensiveInit() is guaranteed to execute only once, even if multiple goroutines call getResource() simultaneously. The simplicity and clarity of this pattern make it a popular choice for lazy initialization and for ensuring certain logic runs exactly once.

Custom Lazy Initialization with Atomic Operations¶

For more granular control or when conditional retries are necessary, atomic operations can be useful:

var initialized atomic.Bool
var resource *MyResource

func getResource() *MyResource {
    if !initialized.Load() {
        if initialized.CompareAndSwap(false, true) {
            resource = expensiveInit()
        }
    }
    return resource
}

Here, atomic operations offer a lock-free alternative to sync.Once, reducing overhead in extremely performance-sensitive scenarios or when the logic must execute once but conditions for initialization can be complex or conditional.

Performance Considerations¶

While lazy initialization can offer clear benefits, it also brings added complexity. It’s important to handle initialization carefully to avoid subtle issues like race conditions or concurrency bugs. Using built-in tools like sync.Once or atomic operations typically ensures thread-safety without much hassle. Still, it’s always a good idea to measure actual improvements through profiling, confirming lazy initialization truly enhances startup speed, reduces memory usage, or boosts your application's responsiveness.

Benchmarking Impact¶

There is typically nothing specific to benchmark with lazy initialization itself, as the main benefit is deferring expensive resource creation. The performance gains are inherently tied to the avoided cost of unnecessary initialization, startup speed improvements, and reduced memory consumption, rather than direct runtime throughput differences.

When to Choose Lazy Initialization¶

When resource initialization is costly or involves I/O. Delaying construction avoids paying the cost of setup—like opening files, querying databases, or loading large structures—unless it’s actually needed.
To improve startup performance and memory efficiency. Deferring work until first use allows your application to start faster and avoid allocating memory for resources that may never be used.
When not all resources are needed immediately or at all during runtime. Lazy initialization helps you avoid initializing fields or services that only apply in specific code paths.
To guarantee a block of code executes exactly once despite repeated calls. Using tools like sync.Once ensures thread-safe, one-time setup in concurrent environments.

Lazy Initialization