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Here's where I've gotten. If anyone has any</div>
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clarifications or suggestions, please let me </div>
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know!</div>
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pstat -f shows 164 / 3404 open files.<br>
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3404 - 164 = 3240</div>
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File # 3248 fails with errno 23.</div>
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On a later test</div>
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pstat shows 166/3404 open files</div>
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3404 -166 = 3238</div>
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File # 3246 fails with errno 23.<br>
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Both times these numbers are off by 8.</div>
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I haven't figured out why exactly fstat is 3 greater than pstat -f, </div>
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nor <span style="font-family: Calibri, Arial, Helvetica, sans-serif; background-color: rgb(255, 255, 255); display: inline !important">
provably<span> </span></span>why there are 8 extra files than expected.</div>
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My hunch about fstat vs pstat difference (3):</div>
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fstat VS pstat has something to do with</div>
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stderr, stdout, and stdin</div>
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My theory about the pstat vs open files difference (8):</div>
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<span style="color: rgb(0, 0, 0); font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt;">There are 7 kqueue filetypes in pstat -f. </span><br>
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If it fails on #3248 (in the first example), </div>
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that means 3247 succeeded.</div>
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<span style="color: rgb(0, 0, 0); font-family: calibri, arial, helvetica, sans-serif; font-size: 12pt; background-color: rgba(0, 0, 0, 0);"> 3247 + 164 = 3,411, which is 7 over 3404</span></div>
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I suspect there's something funky with these kqueue files.</div>
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<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" color="#000000" style="font-size:11pt"><b>From:</b> cs631apue-bounces@lists.stevens.edu <cs631apue-bounces@lists.stevens.edu> on behalf of Jan Schaumann <jschauma@stevens.edu><br>
<b>Sent:</b> Wednesday, September 16, 2020 8:49 AM<br>
<b>To:</b> cs631apue@lists.stevens.edu <cs631apue@lists.stevens.edu><br>
<b>Subject:</b> Re: [cs631apue] Openmax.c fails earlier than expected</font>
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<div class="PlainText">Charles Magyar IV <cmagyar@stevens.edu> wrote:<br>
> If errno == EMFILE, the errno = 24. "Too many open files" according to the man page of errno.<br>
> <br>
> In the else block, errno equals 23 during my run.<br>
> This is ENFILE, and means "Too many open files in system.<br>
> Maximum number of file descriptors allowable on the system has been reached and a request<br>
> for an open cannot be satistfied until at least one has been closed."<br>
> <br>
> So it turns out that the entire system is simply out of space.<br>
<br>
Correct. That is, there's a difference between _a<br>
process_ having reached the limit of how many files it<br>
can open and _the whole system_ having reached its<br>
limit.<br>
<br>
Normally, the limit for a process is smaller than that<br>
of the entire system, but we bumped it to 'unlimited',<br>
meaning we set the per-process limit to be equal to<br>
that of the system-wide limit.<br>
<br>
Since nowe we're talking about the system wide limit,<br>
we are no longer just competing with ourselves, but<br>
with all processes on the system. In other words, any<br>
file open by any other process reduces the number of<br>
files our process can open.<br>
<br>
So the number of files we can open before encountering<br>
ENFILE should be:<br>
<br>
ourfiles = number of files this process can open <br>
otherfiles = number of files open by any other process<br>
max = system wide limit, i.e., 3404 in this case<br>
<br>
ourfiles = max - otherfiles<br>
<br>
> In another test, I ran<br>
> > fstat | wc -l<br>
> > 249<br>
<br>
fstat(1) shows us the open _file descriptors_, but the<br>
limit is on entries in the file table. That is, if a<br>
process has multiple file descriptors pointing to the<br>
same file table entry (such as e.g., duplicated file<br>
descriptors such as when a process has stdin,<br>
stdout, and stderr all connected to terminal), only<br>
the one file table entry counts towards the limit.<br>
<br>
You can use the pstat(1) command with the '-f' flag to<br>
show you the collated mapping; the output includes a<br>
column "CNT" that shows you how many references to<br>
the givenf ile table entry there are.<br>
<br>
You can also use 'fstat -A' to get the relevant object<br>
address, and correlate it with the output of 'pstat'.<br>
For example:<br>
<br>
$ fstat -A | sort -k1,1 | grep pts/0<br>
ffffcf1371e74040 jschauma sh 1995 0 /dev/pts 3 crw--w---- pts/0 rw<br>
ffffcf1371e74040 jschauma sh 1995 1 /dev/pts 3 crw--w---- pts/0 rw<br>
ffffcf1371e74040 jschauma sh 1995 2 /dev/pts 3 crw--w---- pts/0 rw<br>
...<br>
$ fstat -A | sort -k1,1 | grep -c pts/0<br>
17<br>
$ $ pstat -f | grep ffffcf1371e74040<br>
ffffcf1371e74040 file RW 14 0 ffffcf136cc22970 0 372401<br>
<br>
That is, pstat(1) shows us that there are 14<br>
references to /dev/pts/0 (our pseudo-terminal).<br>
<br>
(But fstat(1) showed us 17 - can you find out why<br>
'pstat' showed 3 fewer?)<br>
<br>
Anyway, try to run the same command and compare to the<br>
output of 'pstat -f'. Does that match the number of<br>
files you are then able to open?<br>
<br>
-Jan<br>
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