Escape analysis是Go編譯器在編譯時(shí)進(jìn)行的一種優(yōu)化技術(shù)，用於決定變量是分配在棧還是堆上。 1. 其核心目標(biāo)是盡可能將變量保留在棧中以提高性能；2. 若變量在聲明它的函數(shù)返回後仍被外部引用，如被返回、傳遞給goroutine等，則必須分配到堆上；3. 可通過-gcflags "-m"查看變量逃逸情況；4. 常見導(dǎo)致逃逸的模式包括返回局部變量指針、將變量賦值給interface、向goroutine傳指針、將指針存儲(chǔ)在逃逸的數(shù)據(jù)結(jié)構(gòu)中；5. 逃逸分析有助於減少堆分配，減輕垃圾回收壓力，從而提升性能。

When Go code runs, variables might live on the stack or the heap, and escape analysis is how the Go compiler decides which is which. The goal is to keep as many variables as possible on the stack for better performance, since stack allocation is faster and doesn't require manual memory management. But sometimes, variables need to live longer than the function that created them — and that's when they "escape" to the heap.

What is escape analysis?

Escape analysis is a compile-time optimization in Go that determines the lifetime of variables. If a variable can be safely allocated on the stack — meaning it doesn't outlive the function it was declared in — it stays there. But if it could be referenced outside that function, like being returned or passed to a goroutine, it has to be moved to the heap to avoid dangling references.

You don't usually see this process unless you look into the compiler output, but it plays a big role in performance tuning. And the Go compiler is pretty good at it by default, but understanding how it works can help you write more efficient code.

How to check if a variable escapes

You can use the -gcflags "-m" flag when building or running go build or go run to see where escapes happen. For example:

 go run -gcflags "-m" main.go

The output will tell you things like:

 main.go:10:12: escaping to heap due to return

This helps you identify which variables are ending up on the heap and why. It's especially useful when you're trying to optimize performance-sensitive code.

Some common patterns that cause variables to escape:

• Returning a pointer to a local variable
• Assigning a local variable to an interface
• Sending a pointer to a goroutine
• Storing a pointer in a data structure that escapes

Common escape scenarios

Let's look at a few examples that commonly cause variables to escape.

Returning a pointer to a local variable

 func NewPerson() *Person {
    p := &Person{Name: "Alice"}
    return p
}

Here, p must be allocated on the heap because it's returned and used outside of NewPerson .

Using an interface

 func Log(v interface{}) {
    fmt.Println(v)
}

func main() {
    s := "message"
    Log(s) // s escapes to heap
}

Any concrete type used as an interface{} will escape to the heap because interfaces carry runtime type information and require heap allocation.

Passing pointers to goroutines

 func worker(p *Person) {
    // do something with p
}

func main() {
    p := &Person{Name: "Bob"}
    go worker(p)
}

In this case, p escapes because it's used in a different goroutine whose lifetime is not known at compile time.

How escape analysis helps performance

By keeping variables on the stack when possible, Go avoids unnecessary heap allocations and reduces pressure on the garbage collector. Stack-allocated variables are automatically cleaned up when the function returns, which is fast and efficient.

If a variable escapes to the heap unnecessarily, it means more work for the garbage collector, which can impact performance, especially in high-throughput or latency-sensitive applications.

Avoiding escapes can be a small but meaningful optimization. For example, if you're building a high-performance server that handles thousands of requests per second, reducing heap allocations can lead to lower latency and better throughput.

So while you don't need to think about escape analysis in most day-to-day Go code, knowing how it works helps you make better decisions in performance-critical parts of your code.

基本上就這些。

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