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Make the relationship between mutable histograms and token removal explicit.

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This commit is contained in:
Mike Perry 2019-05-11 03:12:33 +00:00 committed by George Kadianakis
parent 57e5e940d3
commit 5c2d2b5d11
1 changed files with 49 additions and 16 deletions
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65
src/core/or/circuitpadding.c
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@ -330,6 +330,39 @@ circpad_histogram_usec_to_bin(const circpad_machine_runtime_t *mi,
return CIRCPAD_INFINITY_BIN(state)-1;
}
/**
* Return true if the machine supports token removal.
*
* Token removal is equivalent to having a mutable histogram in the
* circpad_machine_runtime_t mutable info. So while we're at it,
* let's assert that everything is consistent between the mutable
* runtime and the readonly machine spec.
*/
static inline int
circpad_is_token_removal_supported(circpad_machine_runtime_t *mi)
{
/* No runtime histogram == no token removal */
if (mi->histogram == NULL) {
/* Machines that don't want token removal are trying to avoid
* potentially expensive mallocs, extra memory accesses, and/or
* potentially expensive monotime calls. Let's minimize checks
* and keep this path fast. */
tor_assert_nonfatal(mi->histogram_len == 0);
return 0;
} else {
/* Machines that do want token removal are less sensitive to performance.
* Let's spend some time to check that our state is consistent and sane */
const circpad_state_t *state = circpad_machine_current_state(mi);
tor_assert_nonfatal(state->token_removal != CIRCPAD_TOKEN_REMOVAL_NONE);
tor_assert_nonfatal(state->histogram_len == mi->histogram_len);
tor_assert_nonfatal(mi->histogram_len != 0);
return 1;
}
tor_assert_nonfatal_unreached();
return 0;
}
/**
* This function frees any token bins allocated from a previous state
*
@ -441,13 +474,7 @@ circpad_machine_sample_delay(circpad_machine_runtime_t *mi)
mi->rtt_estimate_usec + state->dist_added_shift_usec :
state->dist_added_shift_usec;
return circpad_distribution_sample_iat_delay(state, iat_delay_shift);
} else if (state->token_removal != CIRCPAD_TOKEN_REMOVAL_NONE) {
/* We have a mutable histogram. Do basic sanity check and apply: */
if (BUG(!mi->histogram) ||
BUG(mi->histogram_len != state->histogram_len)) {
return CIRCPAD_DELAY_INFINITE;
}
} else if (circpad_is_token_removal_supported(mi)) {
histogram = mi->histogram;
for (circpad_hist_index_t b = 0; b < state->histogram_len; b++)
histogram_total_tokens += histogram[b];
@ -812,7 +839,7 @@ check_machine_token_supply(circpad_machine_runtime_t *mi)
*
* We also do not count infinity bin in histogram totals.
*/
if (mi->histogram_len && mi->histogram) {
if (circpad_is_token_removal_supported(mi)) {
for (circpad_hist_index_t b = 0; b < CIRCPAD_INFINITY_BIN(mi); b++)
histogram_total_tokens += mi->histogram[b];
@ -861,12 +888,8 @@ circpad_machine_count_padding_sent(circpad_machine_runtime_t *mi)
/* If we have a mutable histogram, reduce the token count from
* the chosen padding bin (this assumes we always send padding
* when we intended to). */
if (mi->histogram && mi->histogram_len) {
/* Ensure that we have a token removal strategy set */
const circpad_state_t *state = circpad_machine_current_state(mi);
tor_assert_nonfatal(state->token_removal != CIRCPAD_TOKEN_REMOVAL_NONE);
/* Basic sanity check on the histogram before removing anything */
if (circpad_is_token_removal_supported(mi)) {
/* Check array bounds and token count before removing */
if (!BUG(mi->chosen_bin >= mi->histogram_len) &&
!BUG(mi->histogram[mi->chosen_bin] == 0)) {
mi->histogram[mi->chosen_bin]--;
@ -896,7 +919,7 @@ circpad_machine_count_nonpadding_sent(circpad_machine_runtime_t *mi)
/* Update any state packet length limits that apply */
circpad_machine_update_state_length_for_nonpadding(mi);
/* Remove a token from the histrogram, if applicable */
/* Remove a token from the histogram, if applicable */
circpad_machine_remove_token(mi);
}
@ -1301,7 +1324,17 @@ circpad_machine_schedule_padding,(circpad_machine_runtime_t *mi))
/* in_usec = in microseconds */
in_usec = circpad_machine_sample_delay(mi);
mi->padding_scheduled_at_usec = monotime_absolute_usec();
/* If we're using token removal, we need to know when the padding
* was scheduled at, so we can remove the appropriate token if
* a non-padding cell is sent before the padding timer expires.
*
* However, since monotime is unpredictably expensive, let's avoid
* using it for machines that don't need token removal. */
if (circpad_is_token_removal_supported(mi)) {
mi->padding_scheduled_at_usec = monotime_absolute_usec();
} else {
mi->padding_scheduled_at_usec = 1;
}
log_fn(LOG_INFO,LD_CIRC,"\tPadding in %u usec", in_usec);
// Don't schedule if we have infinite delay.