RFR(s): 8223777: In posix_spawn mode, failing to exec() jspawnhelper does not result in an error

[David Lloyd]

Ah I see.  I like the idea, it would mean pretty comprehensive error
reporting and should work across platforms too I think.

On Tue, May 14, 2019 at 7:16 AM Florian Weimer <fweimer at redhat.com> wrote:
>
> * David Lloyd:
>
> > Pipe communication isn't very costly AFAIK.  The added complexity
> > would be waiting for either a thing to appear on the pipe indicating
> > success or else a waitpid/waitid+WNOHANG for exit code 127.  But
> > writing a thing to the pipe won't help determine if the subsequent
> > exec succeeded, which is really the interesting bit.
>
> Please have a look at the code.  It's already using CLOEXEC to cover
> the execve call (src/java.base/unix/native/libjava/ProcessImpl_md.c):
>
>     switch (readFully(fail[0], &errnum, sizeof(errnum))) {
>     case 0: break; /* Exec succeeded */
>     case sizeof(errnum):
>         waitpid(resultPid, NULL, 0);
>         throwIOException(env, errnum, "Exec failed");
>         goto Catch;
>     default:
>         throwIOException(env, errno, "Read failed");
>         goto Catch;
>     }
>
> Instead of 0/4 bytes, the outcome could be 0/4/8 bytes, corresponding to
> jspawnhelper exec failure, complete success, and exec failure in
> jspawnhelper.
>
> The run-time cost would be the additional pipe write in jspawnhelper.
> There shouldn't even be another ping-pong between the processes.
>
> Thanks,
> Florian



-- 
- DML