intermittent failures on Darwin using java.lang.Process.waitFor()

[David Daney]

Geoffrey Keating wrote:
> The intermittent failures on Darwin are due to a kernel bug tripped by  
> java.lang.Process.waitFor().
> 
> The bug appears to be that if:
> - the program is multithreaded
> - it is blocking SIGCHLD
> - it receives a SIGCHLD due to a process terminating
> - later it calls sigsuspend (but not sigwait)
> 
> then the SIGCHLD may never be delivered, and so the process will wait  
> for one forever.
> 
> It's intermittent because it works fine if the sigsuspend starts  before 
> the SIGCHLD is sent.  This also explains why it happens more  often with 
> gij.
> 
> I've filed this as <rdar://problem/4736203>.  We could work around it  
> by using a timeout of some kind; for example, creating a new thread  
> which sends a SIGCHLD manually after some period of time.  (Obviously,  
> only on Darwin, and maybe only on versions with the bug.)  Do we think  
> this is a good idea?

The obvious solution would be to use a kernel without the bug.  But 
since you want to work around the bug, it seems you want a solution for 
kernels with the bug also.

Your suggestion to have a thread that periodically sends SIGCHLD seems 
like it should work (but would be ugly).  You could have a configure 
test to detect configurations where the workaround was needed.  Then in 
natPosixProcess.cc you would add code to create said thread based on the 
configure check.


David Daney