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Go – SwapUintptr() in sync/atomic package

In this article, we will explore the SwapUintptr() Function in sync/atomic package in Go in details, along with examples.

The SwapUintptr function is part of the “sync/atomic” package in Go which supplies low-level atomic memory operations. This function atomically swaps the value of a uintptr variable with a new value. It is a read-modify-write operation that ensures the value written is immediately visible to other concurrent threads. The function signature is as follows:


func SwapUintptr(addr *uintptr, newVal uintptr) (oldVal uintptr)

The function takes a pointer to a uintptr variable addr and a uintptr value newVal as arguments. It atomically sets the value of addr to newVal and returns the previous value stored in addr.


To illustrate the usage of the SwapUintptr function, let’s create a simple program simulating concurrent data access. We will create two goroutines: one that swaps a shared counter with a new value using the SwapUintptr function and another that reads and prints the counter value using the atomic.LoadUintptr function.

package main

import (






func main() {

	var counter uintptr = 0

	var wg sync.WaitGroup

	// Swapper goroutine

	go func() {

		defer wg.Done()

		for i := 0; i < 5; i++ {

			oldVal := atomic.SwapUintptr(&counter, uintptr(i+1))

			fmt.Printf("Swapper: Counter set to %d (was %d)\n", i+1, oldVal)

			time.Sleep(time.Millisecond * 500)



	// Reader goroutine

	go func() {

		defer wg.Done()

		for i := 0; i < 10; i++ {

			fmt.Printf("Reader: Current counter value is %d\n", atomic.LoadUintptr(&counter))

			time.Sleep(time.Millisecond * 250)





In this example, we use the sync.WaitGroup to ensure that both goroutines complete before the program exits. The swapper goroutine sets the counter value using the atomic.SwapUintptr function and prints the old value, ensuring atomicity. Meanwhile, the reader goroutine reads the counter value using the atomic.LoadUintptr function, guaranteeing that it always reads the latest value written by the swapper goroutine.

This example demonstrates how the SwapUintptr function can be used to perform atomic swap operations on a shared uintptr variable, ensuring data consistency across concurrent threads.


The SwapUintptr function is a valuable utility provided by the sync/atomic package in Go, enabling atomic swap operations on uintptr variables. It is particularly useful in concurrent programming when multiple goroutines access shared memory. Using the SwapUintptr function ensures data consistency and helps eliminate race conditions, contributing to the overall stability and reliability of your concurrent Go applications.

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Posted in golang, packages, sync

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