Cgo: Call Go Function from C Executable, Who Start Go Runtime?

As developers, we often find ourselves in situations where we need to integrate code written in different programming languages. One such scenario is calling Go functions from a C executable. This is where Cgo comes into play. But, have you ever wondered who starts the Go runtime in this process? In this article, we’ll dive into the world of Cgo and explore how to call Go functions from a C executable, and more importantly, who starts the Go runtime.

What is Cgo?

Cgo is a part of the Go programming language that allows developers to call C code from Go and vice versa. It provides a way to integrate C code with Go code, making it possible to leverage the strengths of both languages. Cgo is not a separate language, but rather a bridge between Go and C.

Why Use Cgo?

• Performance: C code can be used to optimize performance-critical parts of a Go program.

• Existing Codebase: Cgo allows you to reuse existing C code and libraries in your Go programs.

• Low-Level Operations: C code can be used to perform low-level operations that are not possible or are difficult to do in Go.

Calling Go Functions from C Executable

To call Go functions from a C executable, you need to create a Go wrappers around the C code. These wrappers will allow you to call Go functions from C.

Step 1: Create a Go Wrapper

// wrapper.go
package main

import "C"
import "fmt"

//export myGoFunction
func myGoFunction() {
    fmt.Println("Hello from Go!")
}

In the above code, we’ve created a Go wrapper that exports a function called `myGoFunction`. This function can be called from C code.

Step 2: Create a C Program

/* main.c */
#include <stdio.h>
#include "_cgo_export.h"

int main() {
    myGoFunction();
    return 0;
}

In the above C program, we’ve included the `_cgo_export.h` header file, which is generated by the Go compiler. This header file contains the declarations for the Go functions exported by the Go wrapper.

Step 3: Compile the Go Wrapper

Compile the Go wrapper using the following command:

$ go build -buildmode=c-shared -o libwrapper.so wrapper.go

This command generates a shared library called `libwrapper.so` that contains the Go wrapper code.

Step 4: Compile the C Program

Compile the C program using the following command:

$ gcc -o main main.c -L. -lwrapper

This command links the C program with the shared library generated in step 3.

Step 5: Run the C Executable

Run the C executable using the following command:

$ ./main

This command runs the C executable, which in turn calls the Go function `myGoFunction`.

Who Starts the Go Runtime?

When you run the C executable, it loads the shared library generated by the Go compiler. The Go runtime is started by the first call to a Go function from the C code. In our example, the Go runtime is started when the C program calls the `myGoFunction` function.

The Go runtime is responsible for managing the Go heap, scheduling Goroutines, and providing other services required by the Go program. When the Go runtime is started, it initializes the Go heap, schedules the Goroutines, and sets up the runtime environment.

How Does the Go Runtime Start?

The Go runtime starts by initializing the following components:

• Heap: The Go heap is initialized with a default size, which can be adjusted using the `GOGC` environment variable.

• Goroutine Scheduler: The Goroutine scheduler is initialized, which is responsible for scheduling Goroutines on available CPU cores.

• System Calls: The Go runtime sets up system calls for I/O operations, such as reading and writing to files, networks, and consoles.

• Memory Management: The Go runtime sets up memory management, including garbage collection and memory allocation.

Once the Go runtime is started, it manages the execution of Go code, including scheduling Goroutines, managing memory, and providing other services required by the Go program.

Conclusion

In this article, we’ve explored how to call Go functions from a C executable using Cgo. We’ve also delved into the mysteries of who starts the Go runtime and how it initializes the Go heap, schedules Goroutines, and sets up the runtime environment.

Cgo provides a powerful way to integrate C code with Go code, allowing developers to leverage the strengths of both languages. By following the steps outlined in this article, you can start calling Go functions from your C executable and take advantage of the performance and flexibility offered by Cgo.

Language	Advantages
Go	High-level abstractions Garbage collection Goroutine scheduling
C	Low-level memory management Performance-critical code Existing codebase

By combining the strengths of both languages, you can create powerful and efficient programs that take advantage of the best of both worlds.

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