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Re: Avoiding SIGPIPE (was Re: OSDL DBT-2 w/ PostgreSQL

From: Manfred Spraul <manfred(at)colorfullife(dot)com>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: Avoiding SIGPIPE (was Re: OSDL DBT-2 w/ PostgreSQL
Date: 2003-11-01 22:25:15
Message-ID: 3FA432CB.1040207@colorfullife.com (view raw or flat)
Thread:
Lists: pgsql-hackers
Tom Lane wrote:

>Manfred Spraul <manfred(at)colorfullife(dot)com> writes:
>  
>
>>What about an option to skip the sigaction calls for apps that can 
>>handle SIGPIPE?
>>    
>>
>
>If the app is ignoring SIGPIPE globally, then our calls will have no
>effect anyway.
>
Wrong. From the opengroup manpage:
<<
SIG_IGN - ignore signal
[snip]
- Setting a signal action to SIG_IGN for a signal that is pending will 
cause the pending signal to be discarded, whether or not it is blocked
    <<
    This is why the kernel spends 20% cpu time processing the SIG_IGN:
    it must walk through all threads of the process and check if there
    are any SIGPIPE signals pending.

>  I don't see that this proposal adds any security.
>  
>
It's not about security: Right now multithreaded apps must call 
signal(SIGPIPE, SIG_IGN), otherwise they could get killed by sudden 
SIGPIPE signals. Additionally, they can't rely on sigpending, because 
the pendings bits are cleared regularly. On top, they get a noticable 
performance hit.

My proposal means that apps that know what they are doing (SIGPIPE 
either SIG_IGN, or blocked, or a suitable handler) can avoid the 
signal(SIGPIPE, SIG_IGN) in pqsecure_write. With backward compatibility, 
because the current system works for single threaded apps.

--
    Manfred


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Subject: Re: Experimental patch for inter-page delay in VACUUM
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Subject: Re: Avoiding SIGPIPE (was Re: OSDL DBT-2 w/ PostgreSQL 7.3.4 and 7.4beta5)

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