golang.org/x/sync v0.0.0-20190423024810-112230192c58: semaphore.NewWeighted

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/sync/semaphore.NewWeighted in pkg:golang/golang.org/x/sync@v0.0.0-20190423024810-112230192c58
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/golang.org/x/sync@v0.0.0-20190423024810-112230192c58
Demonstrate these symbols/APIs:
  - golang.org/x/sync/semaphore.NewWeighted

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:b28cb20997912b8e103c22a44c034b0e3ef12bf7ef1446b3ec93b7e994e50dbf","contract":["semaphore.NewWeighted constructs a non-nil Weighted semaphore with the specified capacity","Weighted.TryAcquire succeeds while requested weight fits remaining capacity and returns false when exceeded","Weighted.Release returns held weight so subsequent acquisitions succeed","Weighted.Acquire acquires weight when available and returns context error when context is already canceled while blocked"],"goal":"verify golang.org/x/sync/semaphore.NewWeighted in pkg:golang/golang.org/x/sync@v0.0.0-20190423024810-112230192c58","kind":"HOW","packages":["pkg:golang/golang.org/x/sync@v0.0.0-20190423024810-112230192c58"],"schemaVersion":1,"symbols":["golang.org/x/sync/semaphore.NewWeighted"]},"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/sync@v0.0.0-20190423024810-112230192c58"],"schemaVersion":1,"subject":"pkg:golang/golang.org/x/sync@v0.0.0-20190423024810-112230192c58","symbols":["golang.org/x/sync/semaphore.NewWeighted"],"verifierAdapter":"golang@1"}

module sample

go 1.21

require golang.org/x/sync v0.0.0-20190423024810-112230192c58

golang.org/x/sync v0.0.0-20190423024810-112230192c58 h1:8gQV6CLnAEikrhgkHFbMAEhagSSnXWGV915qUMm9mrU=
golang.org/x/sync v0.0.0-20190423024810-112230192c58/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=

package main

import (
	"context"
	"fmt"
	"sync"

	"golang.org/x/sync/semaphore"
)

func main() {
	ctx := context.Background()
	sem := semaphore.NewWeighted(2)

	var wg sync.WaitGroup
	for i := 1; i <= 4; i++ {
		wg.Add(1)
		id := i
		go func() {
			defer wg.Done()
			if err := sem.Acquire(ctx, 1); err != nil {
				return
			}
			defer sem.Release(1)
			fmt.Printf("worker %d acquired weight 1\n", id)
		}()
	}
	wg.Wait()

	if sem.TryAcquire(2) {
		fmt.Println("acquired full capacity 2 via TryAcquire")
		sem.Release(2)
	}
}

{
  "schemaVersion": 1,
  "goal": "verify golang.org/x/sync/semaphore.NewWeighted in pkg:golang/golang.org/x/sync@v0.0.0-20190423024810-112230192c58",
  "kind": "HOW",
  "packages": [
    "pkg:golang/golang.org/x/sync@v0.0.0-20190423024810-112230192c58"
  ],
  "symbols": [
    "golang.org/x/sync/semaphore.NewWeighted"
  ]
}

package main

import (
	"context"
	"errors"
	"fmt"
	"os"

	"golang.org/x/sync/semaphore"
)

func main() {
	if err := verifyContract(); err != nil {
		fmt.Fprintf(os.Stderr, "contract failed: %v\n", err)
		os.Exit(1)
	}
	fmt.Println("contract verified")
}

func verifyContract() error {
	// 1. semaphore.NewWeighted constructs a non-nil Weighted semaphore with the specified capacity
	sem := semaphore.NewWeighted(3)
	if sem == nil {
		return errors.New("expected non-nil *semaphore.Weighted")
	}

	// 2. Weighted.TryAcquire succeeds while requested weight fits remaining capacity and returns false when exceeded
	if !sem.TryAcquire(2) {
		return errors.New("expected TryAcquire(2) to succeed on capacity 3")
	}
	if sem.TryAcquire(2) {
		return errors.New("expected second TryAcquire(2) to fail with only 1 remaining")
	}
	if !sem.TryAcquire(1) {
		return errors.New("expected TryAcquire(1) to succeed for remaining capacity 1")
	}
	if sem.TryAcquire(1) {
		return errors.New("expected TryAcquire(1) to fail when capacity is exhausted")
	}

	// 3. Weighted.Release returns held weight so subsequent acquisitions succeed
	sem.Release(2)
	if !sem.TryAcquire(2) {
		return errors.New("expected TryAcquire(2) to succeed after Release(2)")
	}
	sem.Release(3)

	// 4. Weighted.Acquire acquires weight when available and returns context error when context is already canceled while blocked
	ctx := context.Background()
	if err := sem.Acquire(ctx, 3); err != nil {
		return fmt.Errorf("expected Acquire(ctx, 3) to succeed: %w", err)
	}

	canceledCtx, cancel := context.WithCancel(context.Background())
	cancel()
	if err := sem.Acquire(canceledCtx, 1); !errors.Is(err, context.Canceled) {
		return fmt.Errorf("expected context.Canceled on exhausted semaphore, got %v", err)
	}

	sem.Release(3)
	return nil
}