feat: new torrent repository using crossbeam_skiplist::SkipMap

SkipMap is an ordered map based on a lock-free skip list.
It's al alternative to BTreeMap which supports concurrent access across
multiple threads.

One of the performance problems with the current solution is we can only
add one torrent at the time because threads need to lock the whole
BTreeMap. The SkipMap should avoid that problem.

More info about SkiMap:

https://docs.rs/crossbeam-skiplist/latest/crossbeam_skiplist/struct.SkipMap.html#method.remove

The aquatic UDP load test was executed with the current implementation
and the new one:

Current Implementation:

Requests out: 397287.37/second
Responses in: 357549.15/second
  - Connect responses:  177073.94
  - Announce responses: 176905.36
  - Scrape responses:   3569.85
  - Error responses:    0.00
Peers per announce response: 0.00
Announce responses per info hash:
  - p10: 1
  - p25: 1
  - p50: 1
  - p75: 1
  - p90: 2
  - p95: 3
  - p99: 104
  - p99.9: 287
  - p100: 371

New Implementation:

Requests out: 396788.68/second
Responses in: 357105.27/second
  - Connect responses:  176662.91
  - Announce responses: 176863.44
  - Scrape responses:   3578.91
  - Error responses:    0.00
Peers per announce response: 0.00
Announce responses per info hash:
  - p10: 1
  - p25: 1
  - p50: 1
  - p75: 1
  - p90: 2
  - p95: 3
  - p99: 105
  - p99.9: 287
  - p100: 351

The result is pretty similar but the benchmarking for the repository
using criterios shows that this implementations is a litle bit better
than the current one.

cSpell.json

@@ -135,6 +135,7 @@
         "Shareaza",
         "sharktorrent",
         "SHLVL",
+        "skiplist",
         "socketaddr",
         "sqllite",
         "subsec",

packages/torrent-repository/Cargo.toml

@@ -16,11 +16,12 @@ rust-version.workspace = true
 version.workspace = true
 
 [dependencies]
+crossbeam-skiplist = "0.1"
 futures = "0.3.29"
 tokio = { version = "1", features = ["macros", "net", "rt-multi-thread", "signal", "sync"] }
-torrust-tracker-primitives = { version = "3.0.0-alpha.12-develop", path = "../primitives" }
-torrust-tracker-configuration = { version = "3.0.0-alpha.12-develop", path = "../configuration" }
 torrust-tracker-clock = { version = "3.0.0-alpha.12-develop", path = "../clock" }
+torrust-tracker-configuration = { version = "3.0.0-alpha.12-develop", path = "../configuration" }
+torrust-tracker-primitives = { version = "3.0.0-alpha.12-develop", path = "../primitives" }
 
 [dev-dependencies]
 criterion = { version = "0", features = ["async_tokio"] }

packages/torrent-repository/benches/repository_benchmark.rs

@@ -5,7 +5,7 @@ mod helpers;
 use criterion::{criterion_group, criterion_main, Criterion};
 use torrust_tracker_torrent_repository::{
     TorrentsRwLockStd, TorrentsRwLockStdMutexStd, TorrentsRwLockStdMutexTokio, TorrentsRwLockTokio, TorrentsRwLockTokioMutexStd,
-    TorrentsRwLockTokioMutexTokio,
+    TorrentsRwLockTokioMutexTokio, TorrentsSkipMapMutexStd,
 };
 
 use crate::helpers::{asyn, sync};
@@ -45,6 +45,10 @@ fn add_one_torrent(c: &mut Criterion) {
             .iter_custom(asyn::add_one_torrent::<TorrentsRwLockTokioMutexTokio, _>);
     });
 
+    group.bench_function("SkipMapMutexStd", |b| {
+        b.iter_custom(sync::add_one_torrent::<TorrentsSkipMapMutexStd, _>);
+    });
+
     group.finish();
 }
 
@@ -89,6 +93,11 @@ fn add_multiple_torrents_in_parallel(c: &mut Criterion) {
             .iter_custom(|iters| asyn::add_multiple_torrents_in_parallel::<TorrentsRwLockTokioMutexTokio, _>(&rt, iters, None));
     });
 
+    group.bench_function("SkipMapMutexStd", |b| {
+        b.to_async(&rt)
+            .iter_custom(|iters| sync::add_multiple_torrents_in_parallel::<TorrentsSkipMapMutexStd, _>(&rt, iters, None));
+    });
+
     group.finish();
 }
 
@@ -133,6 +142,11 @@ fn update_one_torrent_in_parallel(c: &mut Criterion) {
             .iter_custom(|iters| asyn::update_one_torrent_in_parallel::<TorrentsRwLockTokioMutexTokio, _>(&rt, iters, None));
     });
 
+    group.bench_function("SkipMapMutexStd", |b| {
+        b.to_async(&rt)
+            .iter_custom(|iters| sync::update_one_torrent_in_parallel::<TorrentsSkipMapMutexStd, _>(&rt, iters, None));
+    });
+
     group.finish();
 }
 
@@ -178,6 +192,11 @@ fn update_multiple_torrents_in_parallel(c: &mut Criterion) {
         });
     });
 
+    group.bench_function("SkipMapMutexStd", |b| {
+        b.to_async(&rt)
+            .iter_custom(|iters| sync::update_multiple_torrents_in_parallel::<TorrentsSkipMapMutexStd, _>(&rt, iters, None));
+    });
+
     group.finish();
 }
 

packages/torrent-repository/src/lib.rs

@@ -1,5 +1,6 @@
 use std::sync::Arc;
 
+use repository::skip_map_mutex_std::CrossbeamSkipList;
 use torrust_tracker_clock::clock;
 
 pub mod entry;
@@ -16,6 +17,8 @@ pub type TorrentsRwLockTokio = repository::RwLockTokio<EntrySingle>;
 pub type TorrentsRwLockTokioMutexStd = repository::RwLockTokio<EntryMutexStd>;
 pub type TorrentsRwLockTokioMutexTokio = repository::RwLockTokio<EntryMutexTokio>;
 
+pub type TorrentsSkipMapMutexStd = CrossbeamSkipList<EntryMutexStd>;
+
 /// This code needs to be copied into each crate.
 /// Working version, for production.
 #[cfg(not(test))]

packages/torrent-repository/src/repository/mod.rs

@@ -11,6 +11,7 @@ pub mod rw_lock_std_mutex_tokio;
 pub mod rw_lock_tokio;
 pub mod rw_lock_tokio_mutex_std;
 pub mod rw_lock_tokio_mutex_tokio;
+pub mod skip_map_mutex_std;
 
 use std::fmt::Debug;
 

packages/torrent-repository/src/repository/skip_map_mutex_std.rs

@@ -0,0 +1,106 @@
+use std::collections::BTreeMap;
+use std::sync::Arc;
+
+use crossbeam_skiplist::SkipMap;
+use torrust_tracker_configuration::TrackerPolicy;
+use torrust_tracker_primitives::info_hash::InfoHash;
+use torrust_tracker_primitives::pagination::Pagination;
+use torrust_tracker_primitives::swarm_metadata::SwarmMetadata;
+use torrust_tracker_primitives::torrent_metrics::TorrentsMetrics;
+use torrust_tracker_primitives::{peer, DurationSinceUnixEpoch, PersistentTorrents};
+
+use super::Repository;
+use crate::entry::{Entry, EntrySync};
+use crate::{EntryMutexStd, EntrySingle};
+
+#[derive(Default, Debug)]
+pub struct CrossbeamSkipList<T> {
+    torrents: SkipMap<InfoHash, T>,
+}
+
+impl Repository<EntryMutexStd> for CrossbeamSkipList<EntryMutexStd>
+where
+    EntryMutexStd: EntrySync,
+    EntrySingle: Entry,
+{
+    fn update_torrent_with_peer_and_get_stats(&self, info_hash: &InfoHash, peer: &peer::Peer) -> (bool, SwarmMetadata) {
+        let entry = self.torrents.get_or_insert(*info_hash, Arc::default());
+        entry.value().insert_or_update_peer_and_get_stats(peer)
+    }
+
+    fn get(&self, key: &InfoHash) -> Option<EntryMutexStd> {
+        let maybe_entry = self.torrents.get(key);
+        maybe_entry.map(|entry| entry.value().clone())
+    }
+
+    fn get_metrics(&self) -> TorrentsMetrics {
+        let mut metrics = TorrentsMetrics::default();
+
+        for entry in &self.torrents {
+            let stats = entry.value().lock().expect("it should get a lock").get_stats();
+            metrics.complete += u64::from(stats.complete);
+            metrics.downloaded += u64::from(stats.downloaded);
+            metrics.incomplete += u64::from(stats.incomplete);
+            metrics.torrents += 1;
+        }
+
+        metrics
+    }
+
+    fn get_paginated(&self, pagination: Option<&Pagination>) -> Vec<(InfoHash, EntryMutexStd)> {
+        match pagination {
+            Some(pagination) => self
+                .torrents
+                .iter()
+                .skip(pagination.offset as usize)
+                .take(pagination.limit as usize)
+                .map(|entry| (*entry.key(), entry.value().clone()))
+                .collect(),
+            None => self
+                .torrents
+                .iter()
+                .map(|entry| (*entry.key(), entry.value().clone()))
+                .collect(),
+        }
+    }
+
+    fn import_persistent(&self, persistent_torrents: &PersistentTorrents) {
+        for (info_hash, completed) in persistent_torrents {
+            if self.torrents.contains_key(info_hash) {
+                continue;
+            }
+
+            let entry = EntryMutexStd::new(
+                EntrySingle {
+                    peers: BTreeMap::default(),
+                    downloaded: *completed,
+                }
+                .into(),
+            );
+
+            // Since SkipMap is lock-free the torrent could have been inserted
+            // after checking if it exists.
+            self.torrents.get_or_insert(*info_hash, entry);
+        }
+    }
+
+    fn remove(&self, key: &InfoHash) -> Option<EntryMutexStd> {
+        self.torrents.remove(key).map(|entry| entry.value().clone())
+    }
+
+    fn remove_inactive_peers(&self, current_cutoff: DurationSinceUnixEpoch) {
+        for entry in &self.torrents {
+            entry.value().remove_inactive_peers(current_cutoff);
+        }
+    }
+
+    fn remove_peerless_torrents(&self, policy: &TrackerPolicy) {
+        for entry in &self.torrents {
+            if entry.value().is_good(policy) {
+                continue;
+            }
+
+            entry.remove();
+        }
+    }
+}

src/core/torrent/mod.rs

@@ -26,6 +26,7 @@
 //! Peer that don not have a full copy of the torrent data are called "leechers".
 //!
 
-use torrust_tracker_torrent_repository::TorrentsRwLockStdMutexStd;
+use torrust_tracker_torrent_repository::TorrentsSkipMapMutexStd;
 
-pub type Torrents = TorrentsRwLockStdMutexStd; // Currently Used
+//pub type Torrents = TorrentsRwLockStdMutexStd; // Currently Used
+pub type Torrents = TorrentsSkipMapMutexStd; // Currently Used