Re: Slow signal delivery to server process with heavy I/O

[Dallas Clement <dallas.a.clement@xxxxxxxxx>]

Yes, I have tried setting this flag.  Doesn't seem to make any
difference.  My main thread doesn't do much.  He registers for the
signal and then waits on a self-pipe and wakes up when a signal
arrives.  All the I/O action is happening in the other threads.  I'm
not expecting the other threads to be interrupted during a system call
like 'select', 'send', 'recv' etc, but even if they were, they detect
EINTR and try again.

On Sat, Jul 10, 2010 at 6:26 PM, Gao Free_Wind <gfree.wind@xxxxxxxxx> wrote:
> Do you set the SA_RESTART flag for the signal?
> If set SA_RESTART flag, it will restart the system calls include I/O.
>
> On Sat, Jul 10, 2010 at 4:08 PM, Dallas Clement <dallas.a.clement@xxxxxxxxx>
> wrote:
>>
>> Hi All,
>>
>> I've noticed that asynchronous signals such as SIGINT, SIGTERM etc are
>> delivered to my process long after the signal is sent if the receiving
>> process is handling lots of I/O.  My process is a multi-threaded web
>> server.  It's got one thread waiting on 'select' to accept incoming
>> connections and a thread pool which reads the data with 'recv'.
>>
>> When I batter the web server with incoming traffic and I try to
>> shutdown the server by sending a SIGINT or SIGTERM, I have observed
>> that the web server finishes handling the incoming traffic before the
>> kernel dispatches the signal to the process.  It appears that the
>> 'select' and 'recv' calls are getting highest priority with regard to
>> scheduling.
>>
>> I realize this test may appear unnatural and is perhaps unrealistic,
>> but I would like to be able to shutdown my server gracefully within a
>> reasonable amount of time, no matter what kind of load it is handling.
>>  Don't want to have to wait several minutes for my signals to get
>> handled under heavy load.  Could someone please explain why signal
>> delivery is slow under these conditions?
>>
>> Thanks in advance,
>>
>> Dallas
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