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

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.Pool 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.Pool

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:sha256:7663e9a688c25b655053b591c404d21bf643b2e3e743b995947a57b9ad91d9c3","contract":["puddle.Pool manages resources up to its maximum capacity","puddle.Pool.Acquire retrieves an available resource from the pool","puddle.Pool.CreateResource pre-warms a resource and places it directly into the idle pool","puddle.Pool.AcquireAllIdle atomically acquires all idle resources","puddle.Pool.Stat returns current resource counts including max, total, and idle resources","puddle.Pool.Close closes the pool and causes subsequent acquire calls to return puddle.ErrClosedPool"],"goal":"verify github.com/jackc/puddle.Pool 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.Pool"]},"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.Pool"],"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 Connection struct {
	ID int
}

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

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

	ctx := context.Background()

	// Pre-warm a resource
	if err := pool.CreateResource(ctx); err != nil {
		fmt.Fprintf(os.Stderr, "failed to create resource: %v\n", err)
		os.Exit(1)
	}

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

	conn := res.Value().(*Connection)
	fmt.Printf("acquired connection %d\n", conn.ID)

	stat := pool.Stat()
	fmt.Printf("pool stats: total=%d, acquired=%d, idle=%d\n",
		stat.TotalResources(), stat.AcquiredResources(), stat.IdleResources())

	res.Release()
	fmt.Println("connection released successfully")
}

{
  "schemaVersion": 1,
  "goal": "verify github.com/jackc/puddle.Pool 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.Pool"
  ]
}

package main

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

	"github.com/jackc/puddle"
)

type item struct {
	id int
}

func main() {
	ctx := context.Background()

	// 1. puddle.Pool manages resources up to its maximum capacity
	{
		var created int
		constructor := func(ctx context.Context) (interface{}, error) {
			created++
			return &item{id: created}, nil
		}
		destructor := func(res interface{}) {}

		maxCap := int32(4)
		pool := puddle.NewPool(constructor, destructor, maxCap)
		stat := pool.Stat()
		if stat.MaxResources() != maxCap {
			fmt.Fprintf(os.Stderr, "assertion 1 failed: expected MaxResources %d, got %d\n", maxCap, 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()
	}

	// 2. puddle.Pool.Acquire retrieves an available resource from the pool
	{
		constructor := func(ctx context.Context) (interface{}, error) {
			return &item{id: 42}, nil
		}
		destructor := func(res interface{}) {}

		pool := puddle.NewPool(constructor, destructor, 2)
		res, err := pool.Acquire(ctx)
		if err != nil {
			fmt.Fprintf(os.Stderr, "assertion 2 failed: acquire returned error: %v\n", err)
			os.Exit(1)
		}
		val, ok := res.Value().(*item)
		if !ok || val == nil || val.id != 42 {
			fmt.Fprintf(os.Stderr, "assertion 2 failed: unexpected resource value: %+v\n", val)
			os.Exit(1)
		}
		if pool.Stat().AcquiredResources() != 1 {
			fmt.Fprintf(os.Stderr, "assertion 2 failed: expected 1 acquired resource, got %d\n", pool.Stat().AcquiredResources())
			os.Exit(1)
		}
		res.Release()
		pool.Close()
	}

	// 3. puddle.Pool.CreateResource pre-warms a resource and places it directly into the idle pool
	{
		constructor := func(ctx context.Context) (interface{}, error) {
			return &item{id: 10}, nil
		}
		destructor := func(res interface{}) {}

		pool := puddle.NewPool(constructor, destructor, 3)
		if err := pool.CreateResource(ctx); err != nil {
			fmt.Fprintf(os.Stderr, "assertion 3 failed: CreateResource returned error: %v\n", err)
			os.Exit(1)
		}
		stat := pool.Stat()
		if stat.TotalResources() != 1 {
			fmt.Fprintf(os.Stderr, "assertion 3 failed: expected TotalResources 1, got %d\n", stat.TotalResources())
			os.Exit(1)
		}
		if stat.IdleResources() != 1 {
			fmt.Fprintf(os.Stderr, "assertion 3 failed: expected IdleResources 1, got %d\n", stat.IdleResources())
			os.Exit(1)
		}
		if stat.AcquiredResources() != 0 {
			fmt.Fprintf(os.Stderr, "assertion 3 failed: expected AcquiredResources 0, got %d\n", stat.AcquiredResources())
			os.Exit(1)
		}
		pool.Close()
	}

	// 4. puddle.Pool.AcquireAllIdle atomically acquires all idle resources
	{
		count := 0
		constructor := func(ctx context.Context) (interface{}, error) {
			count++
			return &item{id: count}, nil
		}
		destructor := func(res interface{}) {}

		pool := puddle.NewPool(constructor, destructor, 5)
		if err := pool.CreateResource(ctx); err != nil {
			fmt.Fprintf(os.Stderr, "assertion 4 failed: CreateResource 1 error: %v\n", err)
			os.Exit(1)
		}
		if err := pool.CreateResource(ctx); err != nil {
			fmt.Fprintf(os.Stderr, "assertion 4 failed: CreateResource 2 error: %v\n", err)
			os.Exit(1)
		}

		idleResources := pool.AcquireAllIdle()
		if len(idleResources) != 2 {
			fmt.Fprintf(os.Stderr, "assertion 4 failed: expected 2 idle resources, got %d\n", len(idleResources))
			os.Exit(1)
		}
		if pool.Stat().IdleResources() != 0 {
			fmt.Fprintf(os.Stderr, "assertion 4 failed: expected 0 idle resources after acquire, got %d\n", pool.Stat().IdleResources())
			os.Exit(1)
		}
		if pool.Stat().AcquiredResources() != 2 {
			fmt.Fprintf(os.Stderr, "assertion 4 failed: expected 2 acquired resources, got %d\n", pool.Stat().AcquiredResources())
			os.Exit(1)
		}

		for _, r := range idleResources {
			r.Release()
		}
		pool.Close()
	}

	// 5. puddle.Pool.Stat returns current resource counts including max, total, and idle resources
	{
		constructor := func(ctx context.Context) (interface{}, error) {
			return &item{id: 1}, nil
		}
		destructor := func(res interface{}) {}

		pool := puddle.NewPool(constructor, destructor, 4)
		if err := pool.CreateResource(ctx); err != nil {
			fmt.Fprintf(os.Stderr, "assertion 5 failed: CreateResource error: %v\n", err)
			os.Exit(1)
		}
		stat := pool.Stat()
		if stat.MaxResources() != 4 || stat.TotalResources() != 1 || stat.IdleResources() != 1 || stat.AcquiredResources() != 0 {
			fmt.Fprintf(os.Stderr, "assertion 5 failed: unexpected stats: max=%d, total=%d, idle=%d, acquired=%d\n",
				stat.MaxResources(), stat.TotalResources(), stat.IdleResources(), stat.AcquiredResources())
			os.Exit(1)
		}
		pool.Close()
	}

	// 6. puddle.Pool.Close closes the pool and causes subsequent acquire calls to return puddle.ErrClosedPool
	{
		constructor := func(ctx context.Context) (interface{}, error) {
			return &item{id: 99}, nil
		}
		destructor := func(res interface{}) {}

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

		_, 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.Pool contract assertions passed.")
}