use goroutine pool to avoid the runtime.newstack call

[tiancaiamao]

close #630

Benchmark program

package main

import (
	"context"
	"database/sql"
	"flag"
	"fmt"
	"log"
	"time"
	"sync/atomic"

	"github.com/jamiealquiza/tachymeter"
	_ "github.com/go-sql-driver/mysql"
)

var (
	host     = flag.String("h", "127.0.0.1", "host")
	port     = flag.Int("P", 4000, "port")
	user     = flag.String("u", "root", "username")
	password = flag.String("p", "", "password")
)

func openDB() (*sql.DB, error) {
	dbDSN := fmt.Sprintf("%s:%s@tcp(%s:%d)/test", *user, *password, *host, *port)
	db, err := sql.Open("mysql", dbDSN)
	if err != nil {
		return nil, err
	}
	return db, nil
}

func mustExec(db *sql.DB, query string, args ...interface{}) {
	_, err := db.Exec(query, args...)
	if err != nil {
		log.Fatal(err)
	}
}

func assert(err error) {
	if err != nil {
		log.Fatal(err)
	}
}	

func main() {
	flag.Parse()
	db, err := openDB()
	if err != nil {
		log.Fatal(err)
	}

	mustExec(db, `use test`)
	mustExec(db, `drop table if exists test;`)
	mustExec(db, `create table test (id int unsigned key nonclustered auto_increment) shard_row_id_bits=4 auto_id_cache 1;`)

	t := tachymeter.New(&tachymeter.Config{Size: 300})
	var count int64

	now := time.Now()
	fmt.Println("benchmark start ...")

	for i := 0; i < 64; i++ {
		go func() {
			conn, err := db.Conn(context.Background())
			assert(err)

			_, err = conn.ExecContext(context.Background(), "use test")
			assert(err)

			for {
				start := time.Now()
				_, err := conn.ExecContext(context.Background(), "insert into test values ()")
				assert(err)
				atomic.AddInt64(&count, 1)
				t.AddTime(time.Since(start))
			}
		}()
	}


	tick := time.NewTicker(5 * time.Second)
	for range tick.C {
		total := atomic.LoadInt64(&count)
		fmt.Println("qps ==", total/5)
		atomic.StoreInt64(&count, 0)

		fmt.Println(t.Calc())
		fmt.Println()
	}


	fmt.Println("benchmark end ...", time.Since(now))
}

After this change, the runtime.newstack -> runtime.copystack disappear.

[tiancaiamao]

PTAL @disksing

[sticnarf]

@tiancaiamao Would you please add an Apache-compatible license to your project tiancaiamao/gp?

[sticnarf]

You pointed out the problem in #630 that the goroutine started in startWorker enlarged the stack. But why using goroutine in doActionOnGroupMutations solves the problem in this PR?

[tiancaiamao]

@tiancaiamao Would you please add an Apache-compatible license to your project tiancaiamao/gp?

Done

[tiancaiamao]

You pointed out the problem in #630 that the goroutine started in startWorker enlarged the stack. But why using goroutine in doActionOnGroupMutations solves the problem in this PR?

It's startWorker.func1 which is actually this closure function (closure function is named func1 func2 etc) @sticnarf