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Tolerate a little skew in accounting intervals.

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This will make changes for DST still work, and avoid double-spending
bytes when there are slight changes to configurations.

Fixes bug 1511; the DST issue is a bugfix on 0.0.9pre5.
This commit is contained in:
Nick Mathewson 2010-09-03 12:06:04 -04:00
parent 2081740317
commit 80b3de8753
2 changed files with 34 additions and 4 deletions
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9
changes/bug1511 Normal file
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@ -0,0 +1,9 @@
o Minor bugfixes:
- Tolerate skew in stored vs computed interval starts for bandwidth
accounting. Now, if we change our configuration so that the start
of the period changes by no more than 50% of the period's duration,
we remember bytes that we transferred in the old one. The upshot
of this is that daylight savings time should no longer mess up
bandwidth accounting and make each period potentially happen
twice. Fixes bug 1511; bugfix on 0.0.9pre5.

29
src/or/hibernate.c
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@ -341,6 +341,15 @@ start_of_accounting_period_after(time_t now)
return edge_of_accounting_period_containing(now, 1);
}
/** Return the length of the accounting period containing the time
* <b>now</b>. */
static long
length_of_accounting_period_containing(time_t now)
{
return edge_of_accounting_period_containing(now, 1) -
edge_of_accounting_period_containing(now, 0);
}
/** Initialize the accounting subsystem. */
void
configure_accounting(time_t now)
@ -356,14 +365,26 @@ configure_accounting(time_t now)
log_info(LD_ACCT, "Starting new accounting interval.");
reset_accounting(now);
} else if (interval_start_time ==
start_of_accounting_period_containing(interval_start_time)) {
start_of_accounting_period_containing(interval_start_time)) {
log_info(LD_ACCT, "Continuing accounting interval.");
/* We are in the interval we thought we were in. Do nothing.*/
interval_end_time = start_of_accounting_period_after(interval_start_time);
} else {
log_warn(LD_ACCT,
"Mismatched accounting interval; starting a fresh one.");
reset_accounting(now);
time_t s_now = start_of_accounting_period_containing(interval_start_time);
long duration = length_of_accounting_period_containing(interval_start_time);
double delta = ((double)(s_now - interval_start_time)) / duration;
if (-0.50 <= delta && delta <= 0.50) {
/* The start of the period is now a little later than we remembered.
* That's fine; we might lose a little time, but that's ok. */
log_info(LD_ACCT, "Accounting interval moved by %.02f%%; "
"that's fine.", delta*100);
interval_end_time = start_of_accounting_period_after(interval_start_time);
} else {
log_warn(LD_ACCT,
"Mismatched accounting interval: moved by %.02f%%. "
"Starting a fresh one.", delta*100);
reset_accounting(now);
}
}
accounting_set_wakeup_time();
}