Re: [Chicken-hackers] PATCH: allow signal handlers to be called from any thread.

[Jörg F . Wittenberger]

Thanks Evan.

Am 18.01.2016 um 03:59 schrieb Evan Hanson:
> On 2016-01-15 11:31, Jörg F. Wittenberger wrote:
>> I would not be surprised if an innocent reader would read the code
>> with the comment missing and conclude that we save the local variable
>> `stack_limit` and simply assign C_stack_limit to `saved_stack_limit`,
>> which would bring the bug back.
> 
> There are no innocent readers of CHICKEN's sources.
> 
> More seriously, I think the current text is fine as it clearly explains
> the reason for the assignment.

So be it.  I'm not the native English speaker to eventually judge.

>> However - please correct me if I'm wrong at that - C_cpu_milliseconds
>> will result in yet another system call.  Thus another signal may be
>> dispatched at this point.  And since `pending_interrupts_count` is still
>> zero the first branch of the if statement would be executed again.
> 
> To my knowledge the execution of a system call has no bearing on whether
> a program is liable to receive a signal at a given point, though I may
> certainly be wrong about that.

Not per Unix specification.  But according to my knowledge
implementations usually do this trick.  (But maybe my knowledge is a bit
outdated? Is this text just too old:)

http://www.tldp.org/LDP/tlk/ipc/ipc.html

"""Signals are not presented to the process immediately they are
generated., they must wait until the process is running again. Every
time a process exits from a system call its signal and blocked fields
are checked and, if there are any unblocked signals, they can now be
delivered."""

> In any case, the proper way to avoid this situation is to block other
> signals from arriving during a handler's execution, which CHICKEN
> already does when installing the global signal handler. That's what I

OK, I did not check that one.

Cheers

/Jörg