Initialize a resource only once.
Initialize a resource only once using a complete Go program with explicit sample inputs.
package main
import (
"fmt"
"sync"
)
func main() {
var once sync.Once
count := 0
initialize := func() { count++ }
once.Do(initialize)
once.Do(initialize)
fmt.Println(count)
}Expected output EXAMPLE
1
Details
Save as main.go and run go run main.go with Go 1.26 or later. Uses only the Go standard library. Work in a scratch directory for file examples.
Tested on Ubuntu 24.04.3 LTS · · go version go1.26.9 linux/amd64 · Go standard library
Test inputs, results and environment
The exact published code ran in a dedicated Linux test container with prepared inputs. Dedicated test container, external networking disabled, read-only root, temporary per-example working directory. Browser network requests are blocked. Fixtures and output records are isolated from the application database. Testing covers this example and its stated checks, not every input, operating system, or runtime version. The Linux container shares its host's kernel; this is not a native Windows test.
- Architecture / host kernel
- x86_64 / 6.18.54.1-microsoft-standard-WSL2
- Snippet identity / locale
- uid=65534, gid=65534 (unprivileged) / C.UTF-8
- Interpreter invocation
go run main.go- Container image ID
sha256:c9bce90110f636fe04907469a37e9c8ac888171fd569cbf87101743ec7cdf099- Code SHA-256
8df7c2459b1c866d781450b0929518b5d1d88ec3a2c649fe9b7e5314b1d88ca9- Dependencies
- Go standard library
Test input setup
These are the prepared inputs used by the test harness. See Details above for the prerequisites and how to run this example.
# No input files required.
Observed standard output
1
Exit code: 0. Standard error: empty. Validation: Exact stdout comparison. System-dependent values above are one recorded run.
Additional assertions that passed
Checks recorded by the test harness. Where Python assertions are shown, browser cases use Playwright and simulator cases may inspect pin transitions: result.stdout is captured output, work is the temporary directory, and Path is pathlib.Path. The harness also imports json and csv.
Exact stdout comparison; process returned zero without stderr.