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Date: Sat, 8 Feb 2014 04:40:40 +0400
From: Andrey Repin <anrdaemon AT yandex DOT ru>
Reply-To: Andrey Repin <cygwin AT cygwin DOT com>
Message-ID: <675717060.20140208044040@mtu-net.ru>
To: "Larry Hall (Cygwin)" <cygwin AT cygwin DOT com>
Subject: Re: get rid of getpwent? (Was: cygwin-1.7.28 getpwent header declaration changes ?)
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Greetings, Larry Hall (Cygwin)!

>>>> This takes 7.1 seconds on my system, with a 12-line /etc/passwd file:
>>>>
>>>>       #include <pwd.h>
>>>>       #include <stdio.h>
>>>>       #include <stdlib.h>
>>>>
>>>>       int main(int argc, const char* argv[])
>>>>       {
>>>>           int i;
>>>>           const char* user = argv[1];
>>>>
>>>>           if (!user) {
>>>>               printf("usage: %s username\n", argv[0]);
>>>>               exit(1);
>>>>           }
>>>>
>>>>           for (i = 0; i < 1000000; ++i) {
>>>>               struct passwd* pw = getpwnam(user);
>>>>               if (!pw) {
>>>>                   printf("User %s doesn't exist!\n", user);
>>>>                   exit(2);
>>>>               }
>>>>               else if (i == 0) {
>>>>                   printf("User %s is UID %d\n", user, pw->pw_uid);
>>>>               }
>>>>           }
>>>>       }
>>>>
>>>> So, each getpwnam() call takes 7.1 microseconds on average.
>>>
>>> I think you forgot to put an "exit(0);" after the last printf(). Without
>>> it, you're checking for the same user a million times, which is certainly
>>> going to take a little time. ;-)
>>>
>>
>> I thought the point of the programme /was/ to call getpwnam() a million
>> times. Time this as accurately as you can. Then, with a quick division, you
>> get the time for one call.

> Hm, I missed that he summarized with _microseconds_, even though I quoted
> that too in my response. :-(

> My average was much closer to 2 microseconds per call but that could be
> machine differences.

> In any case, sorry for the noise.

In either case, repeatedly requesting the same record in a short amount of
time will only test the system level cache.


--
WBR,
Andrey Repin (anrdaemon AT yandex DOT ru) 08.02.2014, <04:39>

Sorry for my terrible english...


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