golang.org/x/sys v0.31.0: unix.Eventfd

Clean-room public code sample — generation instructions

Write a brand-new, minimal, self-contained code sample in this clean-room directory.
Do not copy, paraphrase, or reference any existing project source. Work only from this spec.

A csx.json manifest scaffold already exists. Do not recreate it from memory. Preserve its case.goal, packages and symbols; fill its empty case.contract with exact assertions and correct its environment, commands and verifierAdapter for the files you generate.

Goal: verify golang.org/x/sys/unix.Eventfd in pkg:golang/golang.org/x/sys@v0.31.0
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/golang.org/x/sys@v0.31.0
Demonstrate these symbols/APIs:
  - golang.org/x/sys/unix.Eventfd
Constraints:
  - executionContext: node
Required runtime conditions:
  - ecosystem: npm
  - language: javascript
  - moduleSystem: cjs
  - packageManager: npm@10.9.8
  - runtime: node@22.23.2

Rules:
  - One focused purpose; the smallest project that proves the goal.
  - Include a contract test (test/contract.*) that runs OFFLINE and exits 0 exactly when the goal behavior works.
  - Pin every dependency with a lockfile so resolution is reproducible.
  - No secrets, credentials, or tokens. No real URLs (only example.com or localhost). No absolute paths.
  - No personal names, emails, company names, or project identifiers of any kind.
  - No binaries and no generated output (node_modules, dist, target, venv, .git, .env).
  - Keep it under 200 files and 256KB packed.

{"case":{"caseId":"case:sha256:db326d13fa1ee9f406619ad97e6f59eaf3b99bbb542dc965b0645806861c1bbd","contract":["unix.Eventfd creates a file descriptor that accumulates written 8-byte values and resets counter on non-semaphore read","unix.Eventfd with EFD_SEMAPHORE decrements counter by one on each read returning a value of one","unix.Eventfd with EFD_NONBLOCK returns EAGAIN on read when the counter is zero"],"goal":"verify golang.org/x/sys/unix.Eventfd in pkg:golang/golang.org/x/sys@v0.31.0","kind":"HOW","packages":["pkg:golang/golang.org/x/sys@v0.31.0"],"schemaVersion":1,"symbols":["golang.org/x/sys/unix.Eventfd"]},"contractCommand":["go","run","./test"],"environment":{"arch":"x64","distro":"ubuntu","ecosystem":"golang","libc":"glibc","libcVersion":"2.39","os":"linux","osVersionBucket":"24","packageManager":"go","schemaVersion":1},"license":"MIT-0","packages":["pkg:golang/golang.org/x/sys@v0.31.0"],"schemaVersion":1,"subject":"pkg:golang/golang.org/x/sys@v0.31.0","symbols":["golang.org/x/sys/unix.Eventfd"],"verifierAdapter":"golang@1"}

module example.com/sample

go 1.26.0

require golang.org/x/sys v0.31.0

golang.org/x/sys v0.31.0 h1:ioabZlmFYtWhL+TRYpcnNlLwhyxaM9kWTDEmfnprqik=
golang.org/x/sys v0.31.0/go.mod h1:BJP2sWEmIv4KK5OTEluFJCKSidICx8ciO85XgH3Ak8k=

package main

import (
	"encoding/binary"
	"fmt"
	"os"

	"golang.org/x/sys/unix"
)

// CreateEventfd creates an eventfd with given initial value and flags.
func CreateEventfd(initval uint, flags int) (int, error) {
	fd, err := unix.Eventfd(initval, flags)
	if err != nil {
		return -1, fmt.Errorf("unix.Eventfd failed: %w", err)
	}
	return fd, nil
}

// WriteEventfd writes a uint64 value to the eventfd counter.
func WriteEventfd(fd int, val uint64) error {
	var buf [8]byte
	binary.NativeEndian.PutUint64(buf[:], val)
	n, err := unix.Write(fd, buf[:])
	if err != nil {
		return fmt.Errorf("unix.Write failed: %w", err)
	}
	if n != 8 {
		return fmt.Errorf("unix.Write incomplete: wrote %d bytes, expected 8", n)
	}
	return nil
}

// ReadEventfd reads a uint64 value from the eventfd counter.
func ReadEventfd(fd int) (uint64, error) {
	var buf [8]byte
	n, err := unix.Read(fd, buf[:])
	if err != nil {
		return 0, fmt.Errorf("unix.Read failed: %w", err)
	}
	if n != 8 {
		return 0, fmt.Errorf("unix.Read incomplete: read %d bytes, expected 8", n)
	}
	return binary.NativeEndian.Uint64(buf[:]), nil
}

func main() {
	// Standard eventfd demonstration
	fd, err := CreateEventfd(0, unix.EFD_CLOEXEC|unix.EFD_NONBLOCK)
	if err != nil {
		fmt.Fprintf(os.Stderr, "Error creating eventfd: %v\n", err)
		os.Exit(1)
	}
	defer unix.Close(fd)

	if err := WriteEventfd(fd, 42); err != nil {
		fmt.Fprintf(os.Stderr, "Error writing to eventfd: %v\n", err)
		os.Exit(1)
	}

	val, err := ReadEventfd(fd)
	if err != nil {
		fmt.Fprintf(os.Stderr, "Error reading from eventfd: %v\n", err)
		os.Exit(1)
	}
	fmt.Printf("Read value from eventfd: %d\n", val)

	// Semaphore eventfd demonstration
	semFd, err := CreateEventfd(2, unix.EFD_CLOEXEC|unix.EFD_SEMAPHORE|unix.EFD_NONBLOCK)
	if err != nil {
		fmt.Fprintf(os.Stderr, "Error creating semaphore eventfd: %v\n", err)
		os.Exit(1)
	}
	defer unix.Close(semFd)

	semVal1, err := ReadEventfd(semFd)
	if err != nil {
		fmt.Fprintf(os.Stderr, "Error reading semaphore eventfd: %v\n", err)
		os.Exit(1)
	}
	fmt.Printf("First semaphore read: %d\n", semVal1)

	semVal2, err := ReadEventfd(semFd)
	if err != nil {
		fmt.Fprintf(os.Stderr, "Error reading semaphore eventfd: %v\n", err)
		os.Exit(1)
	}
	fmt.Printf("Second semaphore read: %d\n", semVal2)
}

{
  "schemaVersion": 1,
  "goal": "verify golang.org/x/sys/unix.Eventfd in pkg:golang/golang.org/x/sys@v0.31.0",
  "kind": "HOW",
  "packages": [
    "pkg:golang/golang.org/x/sys@v0.31.0"
  ],
  "symbols": [
    "golang.org/x/sys/unix.Eventfd"
  ],
  "constraints": {
    "executionContext": "node"
  },
  "runtimeConditions": {
    "ecosystem": "npm",
    "language": "javascript",
    "moduleSystem": "cjs",
    "packageManager": "npm@10.9.8",
    "runtime": "node@22.23.2"
  }
}

package main

import (
	"encoding/binary"
	"errors"
	"fmt"
	"os"

	"golang.org/x/sys/unix"
)

func main() {
	// Assertion 1: unix.Eventfd creates a file descriptor that accumulates written 8-byte values and resets counter on non-semaphore read
	fd1, err := unix.Eventfd(10, unix.EFD_CLOEXEC|unix.EFD_NONBLOCK)
	if err != nil {
		fmt.Fprintf(os.Stderr, "FAIL: unix.Eventfd failed: %v\n", err)
		os.Exit(1)
	}
	defer unix.Close(fd1)

	var writeBuf [8]byte
	binary.NativeEndian.PutUint64(writeBuf[:], 25)
	n, err := unix.Write(fd1, writeBuf[:])
	if err != nil || n != 8 {
		fmt.Fprintf(os.Stderr, "FAIL: unix.Write failed: n=%d, err=%v\n", n, err)
		os.Exit(1)
	}

	var readBuf [8]byte
	rn, err := unix.Read(fd1, readBuf[:])
	if err != nil || rn != 8 {
		fmt.Fprintf(os.Stderr, "FAIL: unix.Read failed: rn=%d, err=%v\n", rn, err)
		os.Exit(1)
	}

	total := binary.NativeEndian.Uint64(readBuf[:])
	if total != 35 { // 10 initial + 25 written
		fmt.Fprintf(os.Stderr, "FAIL: expected counter 35, got %d\n", total)
		os.Exit(1)
	}

	// Assertion 2: unix.Eventfd with EFD_SEMAPHORE decrements counter by one on each read returning a value of one
	semFd, err := unix.Eventfd(2, unix.EFD_CLOEXEC|unix.EFD_SEMAPHORE|unix.EFD_NONBLOCK)
	if err != nil {
		fmt.Fprintf(os.Stderr, "FAIL: unix.Eventfd with EFD_SEMAPHORE failed: %v\n", err)
		os.Exit(1)
	}
	defer unix.Close(semFd)

	rn1, err := unix.Read(semFd, readBuf[:])
	if err != nil || rn1 != 8 {
		fmt.Fprintf(os.Stderr, "FAIL: semaphore read 1 failed: rn=%d, err=%v\n", rn1, err)
		os.Exit(1)
	}
	val1 := binary.NativeEndian.Uint64(readBuf[:])
	if val1 != 1 {
		fmt.Fprintf(os.Stderr, "FAIL: expected semaphore read value 1, got %d\n", val1)
		os.Exit(1)
	}

	rn2, err := unix.Read(semFd, readBuf[:])
	if err != nil || rn2 != 8 {
		fmt.Fprintf(os.Stderr, "FAIL: semaphore read 2 failed: rn=%d, err=%v\n", rn2, err)
		os.Exit(1)
	}
	val2 := binary.NativeEndian.Uint64(readBuf[:])
	if val2 != 1 {
		fmt.Fprintf(os.Stderr, "FAIL: expected semaphore read value 1, got %d\n", val2)
		os.Exit(1)
	}

	// Assertion 3: unix.Eventfd with EFD_NONBLOCK returns EAGAIN on read when the counter is zero
	emptyFd, err := unix.Eventfd(0, unix.EFD_CLOEXEC|unix.EFD_NONBLOCK)
	if err != nil {
		fmt.Fprintf(os.Stderr, "FAIL: unix.Eventfd with EFD_NONBLOCK failed: %v\n", err)
		os.Exit(1)
	}
	defer unix.Close(emptyFd)

	_, err = unix.Read(emptyFd, readBuf[:])
	if err == nil {
		fmt.Fprintf(os.Stderr, "FAIL: expected error on reading empty non-blocking eventfd, got nil\n")
		os.Exit(1)
	}
	if !errors.Is(err, unix.EAGAIN) && !errors.Is(err, unix.EWOULDBLOCK) {
		fmt.Fprintf(os.Stderr, "FAIL: expected EAGAIN or EWOULDBLOCK, got %v\n", err)
		os.Exit(1)
	}

	fmt.Println("PASS: golang.org/x/sys/unix.Eventfd contract passed")
}