call ngx_localtime may cause deadlock?

Maxim Dounin mdounin at
Fri Mar 5 03:59:21 MSK 2010


On Thu, Mar 04, 2010 at 10:54:56PM +0300, Igor Sysoev wrote:

> On Thu, Mar 04, 2010 at 07:49:57PM +0300, Maxim Dounin wrote:


> > This isn't really relevant though as underlying problem is in 
> > nginx and should be fixed anyway.  Only async-signal-safe 
> > functions may be used in signal handlers, anything else leads to 
> > undefined behaviour.
> Strickly speaking the generic signal handler calls localtime/_r() too:
>     ngx_time_update(0, 0);
> And if timer_resolution bug can be fixed easy, nevertheless, I do not
> know how to log local time in singal handler without localtime().

Well, I see 3 basic options:

1. Handle signals in the event loop (at least kqueue supports it, 
for other methods we may use pipe() to deliver signals to event 
loop safely).  This is basically how libevent does this, btw.

2. Limit signal handlers to use only async-signal-safe functions, 
and nothing more.  This means that time won't be correct (no 
localtime()), errno (if any) won't be translated to text (no 
strerror_r()) etc.

3. Pretend we never talked about it and problems shouldn't happen 
as generic signals are rare (and we already try to follow (2), 
though not completely).

Maxim Dounin

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