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Record Binary Search Refactoring

This commit is contained in:
Patrick Rathje 2021-05-25 20:22:19 +02:00
parent 7909c7968f
commit ecb7bb05ea
5 changed files with 146 additions and 57 deletions
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154
src/ens/records.c
View File

@ -9,16 +9,44 @@
int ens_records_iterator_init_range(record_iterator_t* iterator,
record_sequence_number_t* opt_start,
record_sequence_number_t* opt_end) {
iterator->sn_next = opt_start ? *opt_start : get_oldest_sequence_number();
iterator->sn_end = opt_end ? *opt_end : get_latest_sequence_number();
if (get_num_records() == 0) {
iterator->finished = true; // no contacts -> no iteration :)
} else {
// prevent any changes during initialization
int rc = get_sequence_number_interval(&iterator->sn_next, &iterator->sn_end);
if (rc == 0) {
iterator->finished = false;
// we override start and end with the optional values
if (opt_start) {
iterator->sn_next = *opt_start;
}
if (opt_end) {
iterator->sn_end = *opt_end;
}
} else {
iterator->finished = true;
}
return 0;
}
int64_t get_timestamp_for_sn(record_sequence_number_t sn) {
record_t rec;
if(load_record(&rec, sn) == 0) {
return rec.timestamp;
} else {
return -1;
}
}
enum record_timestamp_search_mode {
RECORD_TIMESTAMP_SEARCH_MODE_MIN,
RECORD_TIMESTAMP_SEARCH_MODE_MAX,
};
/**
* Find an entry via binary search for the timestamp.
*
@ -26,60 +54,76 @@ int ens_records_iterator_init_range(record_iterator_t* iterator,
* @param target timestamp for which to find the nearest entry for
* @param greater flag for indicating, if the loaded sn shall correspond to a greater (1) or smaller (0) timestamp
*/
int find_sn_via_binary_search(record_sequence_number_t* sn_dest, uint32_t target, int greater) {
record_sequence_number_t start = get_oldest_sequence_number();
record_sequence_number_t end = get_latest_sequence_number();
int find_sn_via_binary_search(record_sequence_number_t* sn_dest, uint32_t target, enum record_timestamp_search_mode search_mode) {
record_t dummyRec;
record_sequence_number_t start_sn;
record_sequence_number_t end_sn;
do {
// calculate the contact in the middle between start and end
record_sequence_number_t middle = sn_get_middle_sn(start, end);
// prevent any changes during binary search initialization
// try to load it
int rc = load_record(&dummyRec, middle);
if (rc && rc != -ENS_DELENT && rc != -ENS_NOENT) {
// if our error is not concerning invalid or deleted entries, we just want to return
return rc;
} else if (rc == -ENS_DELENT || rc == -ENS_NOENT) {
int direction = 1;
do {
// increment the calculated "middle" by a certain amount, so we can try to load a new entry
sn_increment_by(middle, direction);
rc = load_record(&dummyRec, middle);
int rc = get_sequence_number_interval(&start_sn, &end_sn);
// alternate around the previously calculated "middle"
// this should avoid deadlocks, because we never read an entry twice
direction += direction > 0 ? 1 : -1;
direction *= -1;
} while (middle >= start && middle <= end && (rc == -ENS_DELENT || rc == -ENS_NOENT));
}
// if we still have an error, just return it
if (rc) {
return rc;
}
// determine the new start and end
if (dummyRec.timestamp > target) {
start = dummyRec.sn;
} else {
end = dummyRec.sn;
}
// break, if we are at the exact timestamp or our start and end are next to each other
} while (dummyRec.timestamp != target && (end - start) > 1);
// TODO lome: maybe loop here aswell?
// increment/decrement the found sn, depending on the greater flag
record_sequence_number_t found = dummyRec.sn;
if (dummyRec.timestamp > target && !greater) {
found--;
} else if (dummyRec.timestamp < target && greater) {
found++;
if (rc) {
return rc;
}
*sn_dest = found;
record_sequence_number_t last_sn = start_sn; // used to check if ran into issues, e.g. could not load the entry or rounding errors
while(!sn_equal(start_sn, end_sn)) {
// calculate the sn in the middle between start and end
record_sequence_number_t cur_sn = sn_get_middle_sn(start_sn, end_sn);
if (sn_equal(cur_sn, last_sn)) {
// if we already checked this entry -> we reduce our boundaries and try again
// this also solves issues with rounding
// TODO: This is not the best way...
if (search_mode == RECORD_TIMESTAMP_SEARCH_MODE_MIN) {
int64_t start_ts = get_timestamp_for_sn(start_sn);
if (start_ts == -1 || start_ts < target) {
// we could not load this entry or this entry is strictly smaller than our target
start_sn = sn_increment(start_sn); // we can safely increment as start_sn < end_sn
} else {
// we actually found the wanted entry!
end_sn = start_sn; // this will break our loop
}
} else {
// we search for the biggest value among them
int64_t end_ts = get_timestamp_for_sn(end_sn);
if (end_ts == -1 || end_ts > target) {
// we could not load this entry or this entry is strictly bigger than our target
end_sn = sn_decrement(end_sn); // we can safely decrement as start_sn < end_sn
} else {
// we actually found the wanted entry!
start_sn = end_sn; // this will break our loop
}
}
} else {
int64_t mid_ts = get_timestamp_for_sn(cur_sn);
if (mid_ts >= 0) {
if (target < mid_ts) {
end_sn = cur_sn;
} else if (target > mid_ts) {
start_sn = cur_sn;
} else {
// target == mid_ts
if (search_mode == RECORD_TIMESTAMP_SEARCH_MODE_MIN) {
// we search for the smallest value among them -> look before this item
end_sn = cur_sn;
} else {
// we search for the biggest value among them -> look after this item
start_sn = cur_sn;
}
}
} else {
// some errors -> we keep the current sn and try to narrow our boundaries
}
}
last_sn = cur_sn;
}
*sn_dest = start_sn; // == end_sn
return 0;
}
@ -96,7 +140,7 @@ int ens_records_iterator_init_timerange(record_iterator_t* iterator, uint32_t* t
}
if (ts_start) {
int rc = find_sn_via_binary_search(&oldest_sn, *ts_start, 1);
int rc = find_sn_via_binary_search(&oldest_sn, *ts_start, RECORD_TIMESTAMP_SEARCH_MODE_MIN);
if (rc) {
return rc;
}
@ -105,7 +149,7 @@ int ens_records_iterator_init_timerange(record_iterator_t* iterator, uint32_t* t
}
if (ts_end) {
int rc = find_sn_via_binary_search(&newest_sn, *ts_end, 0);
int rc = find_sn_via_binary_search(&newest_sn, *ts_end, RECORD_TIMESTAMP_SEARCH_MODE_MAX);
if (rc) {
return rc;
}

14
src/ens/sequencenumber.c
View File

@ -7,7 +7,7 @@
*/
#define GET_MASKED_SN(x) (x & SN_MASK)
int sn_equal(record_sequence_number_t a, record_sequence_number_t b) {
bool sn_equal(record_sequence_number_t a, record_sequence_number_t b) {
return GET_MASKED_SN(a) == GET_MASKED_SN(b);
}
@ -15,10 +15,22 @@ record_sequence_number_t sn_increment(record_sequence_number_t sn) {
return GET_MASKED_SN(++sn);
}
record_sequence_number_t sn_decrement(record_sequence_number_t sn) {
if (sn > 0) {
return GET_MASKED_SN((sn-1));
} else {
return SN_MASK;
}
}
record_sequence_number_t sn_increment_by(record_sequence_number_t sn, uint32_t amount) {
return GET_MASKED_SN((sn + amount));
}
record_sequence_number_t sn_decrement_by(record_sequence_number_t sn, uint32_t amount) {
return sn_increment_by(sn, (SN_MASK+1)-amount);
}
record_sequence_number_t sn_get_middle_sn(record_sequence_number_t older, record_sequence_number_t newer) {
if (older <= newer) {
return GET_MASKED_SN(((older + newer) / 2));

11
src/ens/sequencenumber.h
View File

@ -2,6 +2,7 @@
#define SEQUENCENUMBER_H
#include <stdint.h>
#include <stdbool.h>
typedef uint32_t record_sequence_number_t;
@ -12,7 +13,7 @@ typedef uint32_t record_sequence_number_t;
* @param b second sequence number
* @return 1, if sequence numbers are equal, 0 otherwise.
*/
int sn_equal(record_sequence_number_t a, record_sequence_number_t b);
bool sn_equal(record_sequence_number_t a, record_sequence_number_t b);
/**
* Increment the given sequence number. Wraps around, if 2^24 is reached.
@ -22,6 +23,14 @@ int sn_equal(record_sequence_number_t a, record_sequence_number_t b);
*/
record_sequence_number_t sn_increment(record_sequence_number_t sn);
/**
* Decrement the given sequence number. Wraps around, if 0 is reached.
*
* @param sn sequence number to increment
* @return the incremented sequence number
*/
record_sequence_number_t sn_decrement(record_sequence_number_t sn);
/**
* Increment the given sequence number by a given amount.
*

21
src/ens/storage.c
View File

@ -22,6 +22,8 @@ static ens_fs_t ens_fs;
// Information about currently stored contacts
static stored_records_information_t record_information = {.oldest_contact = 0, .count = 0};
inline storage_id_t convert_sn_to_storage_id(record_sequence_number_t sn) {
return (storage_id_t)(sn % CONFIG_ENS_MAX_CONTACTS);
}
@ -192,6 +194,25 @@ record_sequence_number_t get_oldest_sequence_number() {
return record_information.oldest_contact;
}
int get_sequence_number_interval(record_sequence_number_t* oldest, record_sequence_number_t *latest) {
int ret = -1;
// we lock so that the interval is always valid (e.g. not overlapping)
k_mutex_lock(&info_fs_lock, K_FOREVER);
if (record_information.count > 0) {
if (oldest) {
*oldest = record_information.oldest_contact;
}
if (latest) {
*latest = sn_increment_by(record_information.oldest_contact, record_information.count);
}
ret = 0;
}
k_mutex_unlock(&info_fs_lock);
return ret;
}
uint32_t get_num_records() {
return record_information.count;
}

3
src/ens/storage.h
View File

@ -68,4 +68,7 @@ record_sequence_number_t get_oldest_sequence_number();
*/
uint32_t get_num_records();
int get_sequence_number_interval(record_sequence_number_t* oldest, record_sequence_number_t *latest);
#endif