Question

I try to start a JVM out of a Google Go program that looks like this:

package main
import "fmt"
import "os"
import "log"
func main() {

var name string
name="\\jrex64\\bin\\java.exe"

var path="-Xbootclasspath:jrex64\\lib\\rt.jar;"+
"jrex64\\lib\\jfxrt.jar;"+
"jrex64\\lib\\resources.jar;"+
"jrex64\\lib\\ext\\sunjce_provider.jar;"+
"jrex64\\lib\\ext\\zipfs.jar;"+
"jrex64\\lib\\ext\\sunmscapi.jar;"+
"jrex64\\lib\\ext\\sunec.jar;"+
"jrex64\\lib\\ext\\dnsns.jar;"+
"jrex64\\lib\\ext\\access-bridge-64.jar;"+
"jrex64\\lib\\security\\local_policy.jar;"+
"jrex64\\lib\\jce.jar;"+
"jrex64\\lib\\jfr.jar;"+
"jrex64\\lib\\jsse.jar;"+
"jrex64\\lib\\charsets.jar;"+
"jrex64\\lib\\";



var args[] string=make([]string,4)
args[0]="-verbose"
args[1]=path;
args[2]="-cp Ganesha_lib\\*"
args[3]="-jar Ganesha.jar"

var attr* os.ProcAttr

proc,err:=os.StartProcess(name,args,attr)
proc.Wait();


if err!=nil {
    fmt.Println("an error occurred.\n")
    log.Fatal(err)
}

}

It’s my first Go program. And i’m totally overwhelmed by getting the following error:

panic: runtime error: invalid memory address or nil pointer dereference
[signal 0xc0000005 code=0x0 addr=0x0 pc=0x4278b5]
goroutine 1 [running]:
os.startProcess(0x4aacb4, 0x14, 0xf840001eb0, 0x500000005, 0x0, …)
C:/Users/ADMINI~1/AppData/Local/Temp/2/bindist767862039/go/src/pkg/os/exec_posix.go:28 +0x152
os.StartProcess(0x4aacb4, 0x14, 0xf840001eb0, 0x500000005, 0x0, …)
C:/Users/ADMINI~1/AppData/Local/Temp/2/bindist767862039/go/src/pkg/os/doc.go:24 +0x5c
main.main()
D:/MyGoProject/src/main.go:60 +0x23c
goroutine 2 [syscall]:
created by runtime.main
C:/Users/ADMINI~1/AppData/Local/Temp/2/bindist767862039/go/src/pkg/runtime/proc.c:221
Process finished with exit code 2

How do i have to interpret this error code? What went wrong? And how can i get the JVM startet – it’s situated in a subdirectory of the Go executable file.

Answer 1

It is normally recommended you don’t use os.StartProcess directly. Instead, use os/exec which has a much easier interface. Here is how I would start a java subprocess and wait for it to complete.

http://play.golang.org/p/APlp9KK9wx

package main

import (
    "fmt"
    "log"
    "os/exec"
    "strings"
)

func main() {
    var java = "\\jrex64\\bin\\java.exe"

    var path = []string{
        "jrex64\\lib\\rt.jar",
        "jrex64\\lib\\jfxrt.jar",
        "jrex64\\lib\\resources.jar",
        "jrex64\\lib\\ext\\sunjce_provider.jar",
        "jrex64\\lib\\ext\\zipfs.jar",
        "jrex64\\lib\\ext\\sunmscapi.jar",
        "jrex64\\lib\\ext\\sunec.jar",
        "jrex64\\lib\\ext\\dnsns.jar",
        "jrex64\\lib\\ext\\access-bridge-64.jar",
        "jrex64\\lib\\security\\local_policy.jar",
        "jrex64\\lib\\jce.jar",
        "jrex64\\lib\\jfr.jar",
        "jrex64\\lib\\jsse.jar",
        "jrex64\\lib\\charsets.jar",
        "jrex64\\lib\\",
    }

    pathflag := "-Xbootclasspath:" + strings.Join(path, ";")
    cmd := exec.Command(java, "-verbose", pathflag, "-cp Ganesha_lib\\*", "-jar Ganesha.jar")
    err := cmd.Run()

    if err != nil {
        fmt.Println("an error occurred.\n")
        log.Fatal(err)
    }

}

In case you are curious, the reason you got that panic was that attr is a nil pointer. Instead, you could have done attr := new(os.ProcAttr).