[R] mclapply enters into an infinite loop....

[akshay kulkarni]

Dear Ivan,
                 REgrets to reply this late...

By "holding a lock", you mean a bug in the process right (I am not a computer science guy, excuse my naivete)?

THanking you,
Yours sincerely,
AKSHAY M KULKARNI
________________________________
From: Ivan Krylov <krylov.r00t using gmail.com>
Sent: Thursday, May 18, 2023 1:08 PM
To: akshay kulkarni <akshay_e4 using hotmail.com>
Cc: r-help using r-project.org <r-help using r-project.org>
Subject: Re: [R] mclapply enters into an infinite loop....

On Wed, 17 May 2023 13:55:59 +0000
akshay kulkarni <akshay_e4 using hotmail.com> wrote:

> So that means mclapply should run properly, i.e output a try class
> object and exit. But it didn't. Can you shed some light on why this
> happened?

What's your sessionInfo()? Are you using a GUI frontend?

mclapply() relies on the fork() system call, which is tricky to get
right in a process where other threads may exist at the same time: when
a process calls fork(), the child process ends up with the same
contents of virtual memory but no other threads at all. If a thread was
holding a lock when the process was forked, the lock will never be
released in the child process, leaving it stuck. Depending on how
you're running R, it may be threading issues or something else.

More information may be obtained by looking at traceback() after you
interrupt mclapply() (easy, but low information: did you interrupt
selectChildren() or some other function?) and attaching a C debugger to
the child process when you become sure it's stuck (hard, requires
additional preparation such as installing debugging symbols).

--
Best regards,
Ivan

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