Fix process hangs when daemon starts #373
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daemon/daemon.go
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| return errors.New("cannot find elvish: " + err.Error()) | ||
| } | ||
| binPath = result | ||
| if !filepath.IsAbs(binPath) { |
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I feel that it is better to use the homegrown searching utility (util.Search) in place of exec.LookPath in consistency with the rest of Elvish.
daemon/daemon.go
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| binPath = result | ||
| if !filepath.IsAbs(binPath) { | ||
| var err error | ||
| binPath, err = exec.LookPath(os.Args[0]) |
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The original code has the upside of not crashing when size of os.Args is 0 :).
Also, when Elvish is used as a login shell, os.Args[0] contains -elvish, and this code will search -elvish instead of elvish.
I think the original code is fine here...
daemon/daemon.go
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| "-sock", d.SockPath, | ||
| "-logprefix", d.LogPathPrefix, | ||
| ) | ||
| return cmd.Run() |
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I think it's better to understand what is happening under the scene than using a different interface to do the job :) According to the doc cmd.Run waits for the subprocess to terminate, that is probably some step we should add.
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I think it's better to understand what is happening under the scene than using a different interface to do the job :)
Agreed. The point here is, trying not to re-invent the wheel by using high level API when possible since it is not recommended to use "syscall" package directly according to its doc.
A quick gdb showed the daemon was stuck during the syscall, which remind me to check the flags done internally by exec.Command.
(gdb) bt
#0 syscall.Syscall () at /usr/lib/go-1.8/src/syscall/asm_linux_amd64.s:27
#1 0x000000000047e516 in syscall.readlen (fd=1, p=0xc420125ae0 "", np=8, n=13, err=...) at /usr/lib/go-1.8/src/syscall/zsyscall_linux_amd64.go:1085
#2 0x0000000000478313 in syscall.forkExec (argv0=..., argv=..., attr=0xc420125da0, pid=10, err=...) at /usr/lib/go-1.8/src/syscall/exec_unix.go:202
#3 0x0000000000478754 in syscall.ForkExec (argv0=..., argv=..., attr=0xc420125da0, pid=140729429880769, err=...)
at /usr/lib/go-1.8/src/syscall/exec_unix.go:235
#4 0x0000000000541bfa in github.com/elves/elvish/daemon.forkExec (attr=0xc420125da0, forkLevel=1, binPath=..., dbPath=..., sockPath=..., logPathPrefix=...,
~r6=...) at /home/go/src/github.com/elves/elvish/daemon/daemon.go:120
#5 0x0000000000541a78 in github.com/elves/elvish/daemon.(*Daemon).pseudoFork (d=0xc4201145f0, attr=0xc420125da0, ~r1=842351593000)
at /home/go/src/github.com/elves/elvish/.build/src/github.com/elves/elvish/daemon/daemon.go:104
#6 0x000000000054173a in github.com/elves/elvish/daemon.(*Daemon).Main (d=0xc4201145f0, serve={void (struct string, struct string)} 0xc420125e48,
~r1=14689824) at /home/go/src/github.com/elves/elvish/daemon/daemon.go:67
#7 0x0000000000816869 in main.main () at /home/go/src/github.com/elves/elvish/main.go:121
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It's probably best to use the os/exec interface to implement forkExec.
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Deal. Using os.StartProcess instead to fully close stdin/stdout/stderr.
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daemon/daemon.go
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| // pseudoFork forks a daemon. It is supposed to be called from the daemon. | ||
| func (d *Daemon) pseudoFork(attr *syscall.ProcAttr) int { | ||
| err := forkExec(attr, d.Forked+1, d.BinPath, d.DbPath, d.SockPath, d.LogPathPrefix) | ||
| p, err := os.StartProcess(binPath, []string{ |
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This is repeated below; please make it a function.
The parent hangs on syscall When creating daemon from client. Instead, use highlevel interface to bring daemon up.
The parent hangs on syscall When creating daemon from client. Instead,
use highlevel interface to bring daemon up.