Re: Sporadic superfluous successful exits

[Jim Meyering]

Aki Helin wrote:

> Jim Meyering <address@hidden> wrote:
>
>> Aki Helin wrote:
>> > For some reason Grep appears to occasionally exit with 0 even when there
>> > was no match. This could also be bug Bash, but I wasn't able to reproduce
>> > this with other programs, and the failure seems to be more common with
>> > some patterns, or pairs of a pattern and an input, which would suggest
>> > that the issue is in Grep.
>> > [..]
>>
>> Can you reproduce that on more than one system?
>>
>> With such low frequency, I would suspect your system's RAM or other
>> hardware.  I had a system that was 100% reliable for about six years,
>> but then a few of the big capacitors near the CPU began (very slowly)
>> to bulge and even to leak a little.  By the time 5 or 6 were bulging,
>> I began to see errors and the occasional crash, usually only accompanying
>> heavy disk or network activity.
>
> Yes, this happens on several computers. I also suspected hardware issues
> at first, but this seems to depend too much on what the software does,
> and there have been no issues apart from this on any of the machines.
>
>
>> I've started one of your loops on a debian unstable system using
>> grep-2.10 and zsh.  I will let it run for a few hours.
>
> I left several loops running on several equal machines overnight to get
> some more data. The machines are running 64-bit Debian stable and have
> Atom CPUs, so they're a bit slower than typical desktops.
>
> Machine 1, Bash, Grep 2.6.3
>  - Loop 1: 1 date
>  - Loop 2: 4 dates
>  - Loops 3 and 4 reading from stdin: 0 dates
>
> Machine 2, Dash, Grep 2.6.3
>  - Loop 1: 0 dates
>  - Loop 2: 1 segfault (will drop core next time if this happens again)
>
> Machine 3, Bash, Grep 2.10
>  - Loop 1: 5 dates
>  - Loop 2: 6 dates
>  - Loop 3: 3 dates
>  - Loop 4 reading from stdin: 0 dates

Compiled with which compiler?
Could it be that your Atom-based systems are sometimes too hot?

After 1.5 hours with zsh, and no output, I've switched to bash and dash
in separate windows (it's a 4-core x86_64 system):
  bash -c 'while :; do grep RANDOM cout.sh && date; done'
  dash -c 'while :; do grep RANDOM cout.sh && date; done'

> Machine 4, Bash, Grep 2.10 compiled with Clang & AddressSanitizer
>  - Loops 1, 2 and 3: 0 dates
>
> Machine 5, Zsh, Grep 2.6.3
>  - Loops 1, 2 and 3: 0 dates
>
> I also had a few similar loops running in Bash comparing two files with
> cmp, but all return values stayed nonzero as expected.