Trouble with waitpid and Rust

Matthew Dillon dillon at
Tue Jul 11 09:13:30 PDT 2017

I assume you meant ECHILD?  That would definitely be a bug if there are
still children present after one exits.


On Mon, Jul 10, 2017 at 8:29 AM, Imre Vadász <imrevdsz at> wrote:

> Ok, not related to SIGCHLD or anything like that. What I see when running
> that binary, is that 2 threads are blocking in wait() and when a child
> exit()s, one wait successfully returns. But the other one erronously
> reports SIGCHLD instead of continuing to block as would be expected. This
> definitely looks like a bug in the wait4 syscall, judging from the trace I
> got with "ktrace -i ./test-nix --test-threads 4" here.
> On Monday, July 10, 2017, Imre Vadász <imrevdsz at> wrote:
>> Hi,
>> Did you verify that the child isn't just exiting before the parent calls
>> wait(), and getting reaped by a signal handler for SIGCHLD? This should be
>> easy to verify by running the binary with ktrace. In that case getting
>> ECHILD from waitpid() would be perfectly fine and could be treated as
>> success.
>> Regards, Imre
>> On Monday, July 10, 2017, Michael Neumann <mneumann at> wrote:
>>> On 07/10/17 15:40, Michael Neumann wrote:
>>> > Hi,
>>> >
>>> > I am trying to port some Rust libraries to DragonFly, specifically the
>>> > [nix] crate to access UN*X APIs from Rust.
>>> I think it's related to the problems that can occur when fork()ing a
>>> multi-threaded program, as described here:
>>> wice-before-using-them
>>> Furthermore, I think this is similar to the "cargo" issue I am seeing,
>>> when running multi-threaded (it is forking and execve "rustc" and
>>> probably doing something in between... sometimes it hangs).
>>> Regards,
>>>   Michael
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