crashing pq by specifying runtime.GOMAXPROCS

main.go

package main

import (
	_ "github.com/bmizerany/pq"
	//"runtime"
	"database/sql"
	"log"
	"math/rand"
)

/*
 with linux/x86

 I've come across some weirdness when runtime.GOMAXPROCS(N) where N > 2 on a 
 four core machine. I'm getting crashes of 2 types. It appears to be related 
 to garbage collection. I'm not sure if it's even an issue with the pq package.
  

 8< ------------------------------------------------------------------
    TYPE A 

 throw: gosched of g0
 [signal 0xb code=0x1 addr=0x0 pc=0x804ab44]

 goroutine 1 [running]:

 goroutine 2 [syscall]:
 created by runtime.main
      /usr/custom/goroot/src/pkg/runtime/proc.c:220

 goroutine 3 [syscall]:
 syscall.Syscall6()
      /usr/custom/goroot/src/pkg/syscall/asm_linux_386.s:0 +0x27
 syscall.EpollWait(0x6, 0x188430a8, 0xa, 0xa, 0xffffffff, ...)
      /usr/custom/goroot/src/pkg/syscall/env_unix.go:0 +0x7d
 net.(*pollster).WaitFD(0x188430a0, 0x1883f740, 0x0, 0x0, 0x0, ...)
      /usr/custom/goroot/src/pkg/net/fd_linux.go:146 +0x103
 net.(*pollServer).Run(0x1883f740, 0x0)
      /usr/custom/goroot/src/pkg/net/fd_unix.go:216 +0xdb
 created by net.newPollServer
      /usr/custom/goroot/src/pkg/net/newpollserver_unix.go:33 +0x2c4


 8< ------------------------------------------------------------------
    TYPE B

 panic: invalid memory address or nil pointer dereference
 throw: panic during gc
 [signal 0xb code=0x1 addr=0x0 pc=0x804ace4]

 goroutine 1 [running]:
 github.com/bmizerany/pq.(*conn).recv1(0x18850950, 0x188edff0, 0x5)
      /home/derek/dev/gopath/src/github.com/bmizerany/pq/conn.go:292 +0x104
 github.com/bmizerany/pq.(*stmt).exec(0x188eacc0, 0x188edef0, 0x2)
      /home/derek/dev/gopath/src/github.com/bmizerany/pq/conn.go:479 +0x29f
 github.com/bmizerany/pq.(*stmt).Exec(0x188eacc0, 0x188edef0, 0x2, 0x2, 0x0, ...)
      /home/derek/dev/gopath/src/github.com/bmizerany/pq/conn.go:428 +0xbe
 github.com/bmizerany/pq.(*conn).Exec(0x18850950, 0x188eac80, 0x30, 0x188edef0, 0x2, ...)
      /home/derek/dev/gopath/src/github.com/bmizerany/pq/conn.go:245 +0x137
 database/sql.(*DB).exec(0x188013c0, 0x188eac80, 0x30, 0x62dee0, 0x2, ...)
      /usr/custom/goroot/src/pkg/database/sql/sql.go:357 +0x1af
 database/sql.(*DB).Exec(0x188013c0, 0x188eac80, 0x30, 0x62dee0, 0x2, ...)
      /usr/custom/goroot/src/pkg/database/sql/sql.go:335 +0x74
 main.Insert(0x188013c0, 0x188edd40, 0xa, 0x188e77e0, 0x19, ...)
      /home/derek/dev/gopath/src/pq-bugtest/main.go:122 +0x1eb
 main.main()
      /home/derek/dev/gopath/src/pq-bugtest/main.go:99 +0x327

 goroutine 2 [syscall]:
 created by runtime.main
      /usr/custom/goroot/src/pkg/runtime/proc.c:220

 goroutine 3 [syscall]:
 syscall.Syscall6()
      /usr/custom/goroot/src/pkg/syscall/asm_linux_386.s:0 +0x27
 syscall.EpollWait(0x6, 0x188430a8, 0xa, 0xa, 0xffffffff, ...)
      /usr/custom/goroot/src/pkg/syscall/env_unix.go:0 +0x7d
 net.(*pollster).WaitFD(0x188430a0, 0x1883f740, 0x0, 0x0, 0x0, ...)
      /usr/custom/goroot/src/pkg/net/fd_linux.go:146 +0x103
 net.(*pollServer).Run(0x1883f740, 0x0)
      /usr/custom/goroot/src/pkg/net/fd_unix.go:216 +0xdb
 created by net.newPollServer
      /usr/custom/goroot/src/pkg/net/newpollserver_unix.go:33 +0x2c4

 8< ------------------------------------------------------------------

 To test this you'll need to get into postgres as a superuser and create a user
 and a test db.

 $ psql
 postgres=# CREATE USER warnerb WITH PASSWORD 'passport';
 postgres=# CREATE DATABASE testdb123;

 ----
 The following listing shows when GOMAXPROCS is set to 4,3 and 2, how many 
 insertions were performed prior to crashing. PASS means no crash occured

 with N = 4
 Trials: 
 1: 436
 2: 1555
 3: 1095
 4: 4752
 5: 871
 6: 3604
 7: 1779
 8: 3151
 9: 642

 with N = 3
 Trials:
 1: 1271
 2: 5972
 3: 3801
 4: 1061
 5: 853
 6: 855
 7: 2541
 8: 2757
 9: 1064

 with N = 2
 Trials:
 1: PASS
 2: PASS
 3: PASS
 4: PASS
 5: PASS
 6: PASS
 7: PASS
 8: PASS
 9: PASS

 with N = 1
 Trials:
 1: PASS
 2: PASS
 3: PASS
 4: PASS
 5: PASS
 6: PASS
 7: PASS
 8: PASS
 9: PASS

 !! Omitting call to GOMAXPROCS altogether !!
 Trials:
 1: PASS
 2: PASS
 3: PASS
 4: PASS
 5: PASS
 6: PASS
 7: PASS
 8: PASS
 9: PASS

*/

const createperson = `
create table person (
		did SERIAL,
		unique(did),
		
		name varchar(255),
		email varchar(255),
		unique(email)

		);
`

func main() {
	//runtime.GOMAXPROCS(3)

	cstr := `user=warnerb dbname=testdb123 dbpasswd=passport sslmode=disable`
	db, err := sql.Open("postgres", cstr)
	if err != nil {
		log.Fatal(err)
	}
	defer db.Close()

	// Drop the table if it exists
	_, err = db.Exec(`drop table if exists person cascade;`)
	if err != nil {
		log.Fatal(err, "\ncan't drop table person")
	}

	// Create the table
	_, err = db.Exec(createperson)
	if err != nil {
		log.Fatal(err)
	}

	// Insert a bunch of records. 
	for i := 0; i < 10000; i++ {
		log.Print(i, " ")
		// This is where it will fail, if it does.
		err := Insert(db, RandomName(), RandomEmail())
		if err != nil {
			log.Fatal(err, "\nProblem inserting person")
		}
	}
}

func RandomName() string {
	alphas := `abcdefghijklmnopqrstuvwxyz`
	name := ``
	for i := 0; i < 10; i++ {
		name += string(alphas[rand.Int()%26])
	}
	return name
}

func RandomEmail() string {
	return RandomName() + "@" + RandomName() + ".com"
}

func Insert(db *sql.DB, name, email string) error {
	log.Println("Inserting: ", name, email)
	cols := `(name, email) values ($1,$2) `
	_, err := db.Exec(`INSERT INTO person `+cols, name, email)
	if err != nil {
		return err
	}
	return nil
}