github.com/jackc/puddle v1.1.3: NewPool

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 github.com/jackc/puddle.NewPool in pkg:golang/github.com/jackc/puddle@v1.1.3
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/github.com/jackc/puddle@v1.1.3
Demonstrate these symbols/APIs:
  - github.com/jackc/puddle.NewPool

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:c58d72c07f30cda55daaf067f01acc9901be5f1d959914dc984e05673f000093","contract":["puddle.NewPool initializes a pool with the specified maximum capacity and zero total resources","pool.Acquire constructs and returns a new resource when capacity is available and res.Value retrieves the underlying value","res.Release returns the resource to the pool making it idle, allowing subsequent acquire calls to reuse it","pool.Acquire returns context.DeadlineExceeded when pool capacity is exhausted and acquire context expires","res.Destroy invokes the destructor callback and permanently removes the resource from the pool","pool.Close closes the pool and causes subsequent acquire calls to fail with puddle.ErrClosedPool"],"goal":"verify github.com/jackc/puddle.NewPool in pkg:golang/github.com/jackc/puddle@v1.1.3","kind":"HOW","packages":["pkg:golang/github.com/jackc/puddle@v1.1.3"],"schemaVersion":1,"symbols":["github.com/jackc/puddle.NewPool"]},"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/github.com/jackc/puddle@v1.1.3"],"schemaVersion":1,"subject":"pkg:golang/github.com/jackc/puddle@v1.1.3","symbols":["github.com/jackc/puddle.NewPool"],"verifierAdapter":"golang@1"}

module sample

go 1.26.6

require github.com/jackc/puddle v1.1.3

github.com/davecgh/go-spew v1.1.0 h1:ZDRjVQ15GmhC3fiQ8ni8+OwkZQO4DARzQgrnXU1Liz8=
github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
github.com/jackc/puddle v1.1.3 h1:JnPg/5Q9xVJGfjsO5CPUOjnJps1JaRUm8I9FXVCFK94=
github.com/jackc/puddle v1.1.3/go.mod h1:m4B5Dj62Y0fbyuIc15OsIqK0+JU8nkqQjsgx7dvjSWk=
github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
github.com/stretchr/testify v1.3.0 h1:TivCn/peBQ7UY8ooIcPgZFpTNSz0Q2U6UrFlUfqbe0Q=
github.com/stretchr/testify v1.3.0/go.mod h1:M5WIy9Dh21IEIfnGCwXGc5bZfKNJtfHm1UVUgZn+9EI=

package main

import (
	"context"
	"fmt"
	"os"

	"github.com/jackc/puddle"
)

type Resource struct {
	ID int
}

func main() {
	var count int
	constructor := func(ctx context.Context) (interface{}, error) {
		count++
		return &Resource{ID: count}, nil
	}
	destructor := func(res interface{}) {}

	pool := puddle.NewPool(constructor, destructor, 5)
	defer pool.Close()

	ctx := context.Background()
	res, err := pool.Acquire(ctx)
	if err != nil {
		fmt.Fprintf(os.Stderr, "failed to acquire resource: %v\n", err)
		os.Exit(1)
	}

	val, ok := res.Value().(*Resource)
	if !ok {
		fmt.Fprintf(os.Stderr, "unexpected resource type\n")
		os.Exit(1)
	}
	fmt.Printf("acquired resource ID: %d\n", val.ID)

	res.Release()
	fmt.Println("resource released")
}

{
  "schemaVersion": 1,
  "goal": "verify github.com/jackc/puddle.NewPool in pkg:golang/github.com/jackc/puddle@v1.1.3",
  "kind": "HOW",
  "packages": [
    "pkg:golang/github.com/jackc/puddle@v1.1.3"
  ],
  "symbols": [
    "github.com/jackc/puddle.NewPool"
  ]
}

package main

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

	"github.com/jackc/puddle"
)

type item struct {
	id int
}

func main() {
	// Assertion 1: puddle.NewPool initializes a pool with the specified maximum capacity and zero total resources
	{
		constructor := func(ctx context.Context) (interface{}, error) {
			return &item{id: 1}, nil
		}
		destructor := func(res interface{}) {}

		pool := puddle.NewPool(constructor, destructor, 5)
		stat := pool.Stat()
		if stat.MaxResources() != 5 {
			fmt.Fprintf(os.Stderr, "assertion 1 failed: expected MaxResources 5, got %d\n", stat.MaxResources())
			os.Exit(1)
		}
		if stat.TotalResources() != 0 {
			fmt.Fprintf(os.Stderr, "assertion 1 failed: expected TotalResources 0, got %d\n", stat.TotalResources())
			os.Exit(1)
		}
		pool.Close()
	}

	// Assertion 2: pool.Acquire constructs and returns a new resource when capacity is available and res.Value retrieves the underlying value
	{
		created := 0
		constructor := func(ctx context.Context) (interface{}, error) {
			created++
			return &item{id: created}, nil
		}
		destructor := func(res interface{}) {}

		pool := puddle.NewPool(constructor, destructor, 3)
		ctx := context.Background()

		res, err := pool.Acquire(ctx)
		if err != nil {
			fmt.Fprintf(os.Stderr, "assertion 2 failed: unexpected acquire error: %v\n", err)
			os.Exit(1)
		}
		val, ok := res.Value().(*item)
		if !ok || val.id != 1 {
			fmt.Fprintf(os.Stderr, "assertion 2 failed: unexpected item value: %+v\n", val)
			os.Exit(1)
		}
		if pool.Stat().AcquiredResources() != 1 {
			fmt.Fprintf(os.Stderr, "assertion 2 failed: expected AcquiredResources 1, got %d\n", pool.Stat().AcquiredResources())
			os.Exit(1)
		}
		res.Release()
		pool.Close()
	}

	// Assertion 3: res.Release returns the resource to the pool making it idle, allowing subsequent acquire calls to reuse it
	{
		created := 0
		constructor := func(ctx context.Context) (interface{}, error) {
			created++
			return &item{id: created}, nil
		}
		destructor := func(res interface{}) {}

		pool := puddle.NewPool(constructor, destructor, 2)
		ctx := context.Background()

		res1, err := pool.Acquire(ctx)
		if err != nil {
			fmt.Fprintf(os.Stderr, "assertion 3 failed: acquire 1 error: %v\n", err)
			os.Exit(1)
		}
		res1.Release()

		if pool.Stat().IdleResources() != 1 {
			fmt.Fprintf(os.Stderr, "assertion 3 failed: expected 1 idle resource, got %d\n", pool.Stat().IdleResources())
			os.Exit(1)
		}

		res2, err := pool.Acquire(ctx)
		if err != nil {
			fmt.Fprintf(os.Stderr, "assertion 3 failed: acquire 2 error: %v\n", err)
			os.Exit(1)
		}
		if created != 1 || res2.Value().(*item).id != 1 {
			fmt.Fprintf(os.Stderr, "assertion 3 failed: resource was not reused\n")
			os.Exit(1)
		}
		res2.Release()
		pool.Close()
	}

	// Assertion 4: pool.Acquire returns context.DeadlineExceeded when pool capacity is exhausted and acquire context expires
	{
		constructor := func(ctx context.Context) (interface{}, error) {
			return &item{id: 42}, nil
		}
		destructor := func(res interface{}) {}

		pool := puddle.NewPool(constructor, destructor, 1)
		ctx := context.Background()

		res, err := pool.Acquire(ctx)
		if err != nil {
			fmt.Fprintf(os.Stderr, "assertion 4 failed: acquire error: %v\n", err)
			os.Exit(1)
		}

		timeoutCtx, cancel := context.WithTimeout(ctx, 50*time.Millisecond)
		_, err = pool.Acquire(timeoutCtx)
		cancel()
		if !errors.Is(err, context.DeadlineExceeded) {
			fmt.Fprintf(os.Stderr, "assertion 4 failed: expected context.DeadlineExceeded, got: %v\n", err)
			os.Exit(1)
		}

		res.Release()
		pool.Close()
	}

	// Assertion 5: res.Destroy invokes the destructor callback and permanently removes the resource from the pool
	{
		destructChan := make(chan int, 1)
		constructor := func(ctx context.Context) (interface{}, error) {
			return &item{id: 99}, nil
		}
		destructor := func(res interface{}) {
			destructChan <- res.(*item).id
		}

		pool := puddle.NewPool(constructor, destructor, 2)
		ctx := context.Background()

		res, err := pool.Acquire(ctx)
		if err != nil {
			fmt.Fprintf(os.Stderr, "assertion 5 failed: acquire error: %v\n", err)
			os.Exit(1)
		}

		res.Destroy()

		select {
		case destroyedID := <-destructChan:
			if destroyedID != 99 {
				fmt.Fprintf(os.Stderr, "assertion 5 failed: unexpected destroyed id: %d\n", destroyedID)
				os.Exit(1)
			}
		case <-time.After(1 * time.Second):
			fmt.Fprintf(os.Stderr, "assertion 5 failed: destructor not called\n")
			os.Exit(1)
		}

		if pool.Stat().TotalResources() != 0 {
			fmt.Fprintf(os.Stderr, "assertion 5 failed: expected TotalResources 0 after Destroy, got %d\n", pool.Stat().TotalResources())
			os.Exit(1)
		}
		pool.Close()
	}

	// Assertion 6: pool.Close closes the pool and causes subsequent acquire calls to fail with puddle.ErrClosedPool
	{
		constructor := func(ctx context.Context) (interface{}, error) {
			return &item{id: 100}, nil
		}
		destructor := func(res interface{}) {}

		pool := puddle.NewPool(constructor, destructor, 2)
		pool.Close()

		ctx := context.Background()
		_, err := pool.Acquire(ctx)
		if !errors.Is(err, puddle.ErrClosedPool) {
			fmt.Fprintf(os.Stderr, "assertion 6 failed: expected puddle.ErrClosedPool, got: %v\n", err)
			os.Exit(1)
		}
	}

	fmt.Println("All puddle.NewPool contract assertions passed.")
}