SIGCHLD wakes up time.Sleep

[gopherbot]

by gfranxman:

What steps will reproduce the problem?
1. Calling ForkExec
2. Calling time.Sleep

--- example ---
package main

import "fmt"
import "os"
import "time"

func main() {
    fmt.Printf("First 5 sec Sleep\n" ) ;
    time.Sleep(1000* 1000*1000 * 5) ;

    // forkexec seems to break the timer
    pid, err := os.ForkExec("/bin/date", []string{"date"}, os.Environ(),
"", []*os.File{os.Stdin, os.Stdout, os.Stderr});
    fmt.Printf( "pid, err:%d, %d\n" , pid, err ) ;

    fmt.Printf("Second 5 sec Sleep\n" ) ;
    time.Sleep(1000* 1000*1000 * 5) ;

    fmt.Printf("Done\n" ) ;
}
--- /example --


What is the expected output? What do you see instead?

I would expect the example program to output "First 5 sec Sleep" then pause
for 5 seconds, then output "Second 5 sec Sleep" and pause for 5 more
seconds before printing "Done".    The output from the ForkExec'd /bin/date
command should shouw up asynchonously.

What is your $GOOS?  $GOARCH?
GOARCH=amd64
GOOS=linux


Which revision are you sync'ed to?  (hg log -l 1)

$ hg log -l 1
changeset:   4108:d1b75410b793
tag:         tip
user:        Adam Langley <agl@golang.org>
date:        Tue Nov 17 18:21:47 2009 -0800
summary:     crypto/rsa: add PKCS#1 v1.5 signature support.

[rsc]

Comment 1:

The problem is that when the forked /bin/date
exits, Sleep gets a signal and doesn't restart.
It's hard to know what to do here in general--this is
really a question of Unix semantics, not Go semantics--
but I think the solution is to not allow SIGCHLD to interrupt
system calls.

Owner changed to r...@golang.org.

Status changed to Accepted.

[gopherbot]

Comment 2 by gfranxman:

Confirmed.    This functions as expected:
--- Example ---
package main
import "fmt"
import "os"
import "time"
import "syscall"
func main() {
    var wstatus syscall.WaitStatus;
    fmt.Printf("First 5 sec Sleep\n" ) ;
    time.Sleep(1000* 1000*1000 * 5) ;
    // wait must be called on the forked proc, otherwise the SIGCHILD interferes with
the subsequent call to time.Sleep
    pid, forkerr := os.ForkExec("/bin/date", []string{"date"}, os.Environ(), "",
[]*os.File{os.Stdin, os.Stdout, os.Stderr});
    _, waiterr := syscall.Wait4(pid, &wstatus, 0, nil);
    fmt.Printf( "pid, forkerr, waiterr:%d, %d, %d\n" , pid, forkerr, waiterr ) ;
    fmt.Printf("Second 5 sec Sleep\n" ) ;
    time.Sleep(1000* 1000*1000 * 5) ;
    fmt.Printf("Done\n" ) ;
}
--- /Example ---
  
Probably should be using the exec.Cmd struct for this type of functionality.

[rsc]

Comment 3:

Labels changed: added packagebug.

[rsc]

Comment 4:

thanks to cw@f00f.org

Status changed to Fixed.