Parallelize DFS, use an AtomicBool for short-circuiting

time:   [73.407 µs 76.145 µs 79.345 µs]
change: [−40.126% −24.679% −3.8062%] (p = 0.04 < 0.05)

justfile

@@ -22,6 +22,9 @@ test-integration:
 test-all:
     cd {{tauri_path}} && cargo test --release -- --nocapture
 
+bench:
+    cd {{tauri_path}} && cargo bench
+
 # profile:
 #     cd {{tauri_path}} && cargo flamegraph
 

src-tauri/Cargo.lock

@@ -43,6 +43,15 @@ dependencies = [
  "alloc-no-stdlib",
 ]
 
+[[package]]
+name = "alloca"
+version = "0.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e5a7d05ea6aea7e9e64d25b9156ba2fee3fdd659e34e41063cd2fc7cd020d7f4"
+dependencies = [
+ "cc",
+]
+
 [[package]]
 name = "android_log-sys"
 version = "0.3.2"
@@ -69,6 +78,18 @@ dependencies = [
  "libc",
 ]
 
+[[package]]
+name = "anes"
+version = "0.1.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "4b46cbb362ab8752921c97e041f5e366ee6297bd428a31275b9fcf1e380f7299"
+
+[[package]]
+name = "anstyle"
+version = "1.0.13"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5192cca8006f1fd4f7237516f40fa183bb07f8fbdfedaa0036de5ea9b0b45e78"
+
 [[package]]
 name = "anyhow"
 version = "1.0.100"
@@ -489,6 +510,12 @@ dependencies = [
  "toml 0.9.8",
 ]
 
+[[package]]
+name = "cast"
+version = "0.3.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "37b2a672a2cb129a2e41c10b1224bb368f9f37a2b16b612598138befd7b37eb5"
+
 [[package]]
 name = "cc"
 version = "1.2.49"
@@ -552,6 +579,58 @@ dependencies = [
  "windows-link 0.2.1",
 ]
 
+[[package]]
+name = "ciborium"
+version = "0.2.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "42e69ffd6f0917f5c029256a24d0161db17cea3997d185db0d35926308770f0e"
+dependencies = [
+ "ciborium-io",
+ "ciborium-ll",
+ "serde",
+]
+
+[[package]]
+name = "ciborium-io"
+version = "0.2.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "05afea1e0a06c9be33d539b876f1ce3692f4afea2cb41f740e7743225ed1c757"
+
+[[package]]
+name = "ciborium-ll"
+version = "0.2.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "57663b653d948a338bfb3eeba9bb2fd5fcfaecb9e199e87e1eda4d9e8b240fd9"
+dependencies = [
+ "ciborium-io",
+ "half",
+]
+
+[[package]]
+name = "clap"
+version = "4.5.56"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a75ca66430e33a14957acc24c5077b503e7d374151b2b4b3a10c83b4ceb4be0e"
+dependencies = [
+ "clap_builder",
+]
+
+[[package]]
+name = "clap_builder"
+version = "4.5.56"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "793207c7fa6300a0608d1080b858e5fdbe713cdc1c8db9fb17777d8a13e63df0"
+dependencies = [
+ "anstyle",
+ "clap_lex",
+]
+
+[[package]]
+name = "clap_lex"
+version = "0.7.7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c3e64b0cc0439b12df2fa678eae89a1c56a529fd067a9115f7827f1fffd22b32"
+
 [[package]]
 name = "color_quant"
 version = "1.1.0"
@@ -651,6 +730,41 @@ dependencies = [
  "cfg-if",
 ]
 
+[[package]]
+name = "criterion"
+version = "0.8.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "4d883447757bb0ee46f233e9dc22eb84d93a9508c9b868687b274fc431d886bf"
+dependencies = [
+ "alloca",
+ "anes",
+ "cast",
+ "ciborium",
+ "clap",
+ "criterion-plot",
+ "itertools 0.13.0",
+ "num-traits",
+ "oorandom",
+ "page_size",
+ "plotters",
+ "rayon",
+ "regex",
+ "serde",
+ "serde_json",
+ "tinytemplate",
+ "walkdir",
+]
+
+[[package]]
+name = "criterion-plot"
+version = "0.8.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ed943f81ea2faa8dcecbbfa50164acf95d555afec96a27871663b300e387b2e4"
+dependencies = [
+ "cast",
+ "itertools 0.13.0",
+]
+
 [[package]]
 name = "crossbeam-channel"
 version = "0.5.15"
@@ -660,12 +774,37 @@ dependencies = [
  "crossbeam-utils",
 ]
 
+[[package]]
+name = "crossbeam-deque"
+version = "0.8.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9dd111b7b7f7d55b72c0a6ae361660ee5853c9af73f70c3c2ef6858b950e2e51"
+dependencies = [
+ "crossbeam-epoch",
+ "crossbeam-utils",
+]
+
+[[package]]
+name = "crossbeam-epoch"
+version = "0.9.18"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5b82ac4a3c2ca9c3460964f020e1402edd5753411d7737aa39c3714ad1b5420e"
+dependencies = [
+ "crossbeam-utils",
+]
+
 [[package]]
 name = "crossbeam-utils"
 version = "0.8.21"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "d0a5c400df2834b80a4c3327b3aad3a4c4cd4de0629063962b03235697506a28"
 
+[[package]]
+name = "crunchy"
+version = "0.2.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "460fbee9c2c2f33933d720630a6a0bac33ba7053db5344fac858d4b8952d77d5"
+
 [[package]]
 name = "crypto-common"
 version = "0.1.7"
@@ -1523,6 +1662,17 @@ dependencies = [
  "syn 2.0.111",
 ]
 
+[[package]]
+name = "half"
+version = "2.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6ea2d84b969582b4b1864a92dc5d27cd2b77b622a8d79306834f1be5ba20d84b"
+dependencies = [
+ "cfg-if",
+ "crunchy",
+ "zerocopy",
+]
+
 [[package]]
 name = "hashbrown"
 version = "0.12.3"
@@ -1883,6 +2033,15 @@ dependencies = [
  "once_cell",
 ]
 
+[[package]]
+name = "itertools"
+version = "0.13.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "413ee7dfc52ee1a4949ceeb7dbc8a33f2d6c088194d9f922fb8318faf1f01186"
+dependencies = [
+ "either",
+]
+
 [[package]]
 name = "itertools"
 version = "0.14.0"
@@ -2509,6 +2668,12 @@ version = "1.21.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "42f5e15c9953c5e4ccceeb2e7382a716482c34515315f7b03532b8b4e8393d2d"
 
+[[package]]
+name = "oorandom"
+version = "11.1.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d6790f58c7ff633d8771f42965289203411a5e5c68388703c06e14f24770b41e"
+
 [[package]]
 name = "open"
 version = "5.3.3"
@@ -2537,6 +2702,16 @@ dependencies = [
  "pin-project-lite",
 ]
 
+[[package]]
+name = "page_size"
+version = "0.6.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "30d5b2194ed13191c1999ae0704b7839fb18384fa22e49b57eeaa97d79ce40da"
+dependencies = [
+ "libc",
+ "winapi",
+]
+
 [[package]]
 name = "pango"
 version = "0.18.3"
@@ -2779,6 +2954,34 @@ dependencies = [
  "time",
 ]
 
+[[package]]
+name = "plotters"
+version = "0.3.7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5aeb6f403d7a4911efb1e33402027fc44f29b5bf6def3effcc22d7bb75f2b747"
+dependencies = [
+ "num-traits",
+ "plotters-backend",
+ "plotters-svg",
+ "wasm-bindgen",
+ "web-sys",
+]
+
+[[package]]
+name = "plotters-backend"
+version = "0.3.7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "df42e13c12958a16b3f7f4386b9ab1f3e7933914ecea48da7139435263a4172a"
+
+[[package]]
+name = "plotters-svg"
+version = "0.3.7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "51bae2ac328883f7acdfea3d66a7c35751187f870bc81f94563733a154d7a670"
+dependencies = [
+ "plotters-backend",
+]
+
 [[package]]
 name = "png"
 version = "0.17.16"
@@ -3070,6 +3273,26 @@ version = "0.6.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "20675572f6f24e9e76ef639bc5552774ed45f1c30e2951e1e99c59888861c539"
 
+[[package]]
+name = "rayon"
+version = "1.11.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "368f01d005bf8fd9b1206fb6fa653e6c4a81ceb1466406b81792d87c5677a58f"
+dependencies = [
+ "either",
+ "rayon-core",
+]
+
+[[package]]
+name = "rayon-core"
+version = "1.13.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "22e18b0f0062d30d4230b2e85ff77fdfe4326feb054b9783a3460d8435c8ab91"
+dependencies = [
+ "crossbeam-deque",
+ "crossbeam-utils",
+]
+
 [[package]]
 name = "redox_syscall"
 version = "0.5.18"
@@ -3224,10 +3447,12 @@ version = "0.1.0"
 dependencies = [
  "anyhow",
  "chrono",
+ "criterion",
  "docx-rs",
- "itertools",
+ "itertools 0.14.0",
  "log",
  "rand 0.9.2",
+ "rayon",
  "rstest",
  "serde",
  "serde_json",
@@ -4272,6 +4497,16 @@ dependencies = [
  "zerovec",
 ]
 
+[[package]]
+name = "tinytemplate"
+version = "1.2.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "be4d6b5f19ff7664e8c98d03e2139cb510db9b0a60b55f8e8709b689d939b6bc"
+dependencies = [
+ "serde",
+ "serde_json",
+]
+
 [[package]]
 name = "tinyvec"
 version = "1.10.0"

src-tauri/Cargo.toml

@@ -30,3 +30,19 @@ log = "0.4.29"
 rand = "0.9.2"
 docx-rs = "0.4.18"
 anyhow = "1.0.100"
+rayon = "1.11"
+
+[dev-dependencies]
+criterion = { version = "0.8.1", features = ["html_reports"] }
+
+[[bench]]
+name = "rayon"
+harness = false
+
+[lints.clippy]
+indexing_slicing = "deny"
+fallible_impl_from = "deny"
+wildcard_enum_match_arm = "deny"
+unneeded_field_pattern = "deny"
+fn_params_excessive_bools = "deny"
+# must_use_candidate = "deny"

src-tauri/benches/rayon.rs

@@ -0,0 +1,53 @@
+use std::hint::black_box;
+
+use criterion::{criterion_group, criterion_main, Criterion};
+use rota_lib::{
+    config::{ToxicPair, UserConfig},
+    resident::Resident,
+    schedule::{MonthlySchedule, ShiftType},
+    scheduler::Scheduler,
+    slot::Day,
+    workload::WorkloadTracker,
+};
+
+fn criterion_benchmark(c: &mut Criterion) {
+    let config = maximal_config();
+    let scheduler = Scheduler::new_with_config(config);
+
+    c.bench_function("scheduler run", |b| {
+        b.iter(|| {
+            let mut schedule = MonthlySchedule::new();
+            let mut tracker = WorkloadTracker::default();
+            let result = scheduler.run(&mut schedule, &mut tracker);
+            black_box(result)
+        })
+    });
+}
+
+fn maximal_config() -> UserConfig {
+    UserConfig::default()
+        .with_holidays(vec![2, 3, 10, 11, 12, 25])
+        .with_residents(vec![
+            Resident::new(1, "R1").with_max_shifts(3),
+            Resident::new(2, "R2").with_max_shifts(4),
+            Resident::new(3, "R3").with_reduced_load(),
+            Resident::new(4, "R4").with_allowed_types(vec![ShiftType::Closed]),
+            Resident::new(5, "R5")
+                .with_allowed_types(vec![ShiftType::OpenFirst, ShiftType::OpenSecond]),
+            Resident::new(6, "R6").with_negative_shifts(vec![Day(5), Day(15), Day(25)]),
+            Resident::new(7, "R7")
+                .with_allowed_types(vec![ShiftType::OpenFirst, ShiftType::OpenSecond]),
+            Resident::new(8, "R8"),
+            Resident::new(9, "R9"),
+            Resident::new(10, "R10").with_reduced_load(),
+        ])
+        .with_toxic_pairs(vec![
+            ToxicPair::new(1, 2),
+            ToxicPair::new(3, 4),
+            ToxicPair::new(3, 5),
+            ToxicPair::new(7, 8),
+        ])
+}
+
+criterion_group!(benches, criterion_benchmark);
+criterion_main!(benches);

src-tauri/src/scheduler.rs

@@ -1,3 +1,5 @@
+use std::sync::atomic::{AtomicBool, Ordering};
+
 use crate::{
     config::UserConfig,
     resident::ResidentId,
@@ -7,7 +9,10 @@ use crate::{
     workload::{WorkloadBounds, WorkloadTracker},
 };
 
+use anyhow::bail;
+use log::warn;
 use rand::Rng;
+use rayon::iter::{IntoParallelRefIterator, ParallelIterator};
 
 pub struct Scheduler {
     pub config: UserConfig,
@@ -46,7 +51,46 @@ impl Scheduler {
 
         //TODO: add validation
 
-        self.search(schedule, tracker, Slot::default())
+        // find first non-manually-filled slot
+        let slot = (0..=self.config.total_slots)
+            .find(|&slot_idx| !schedule.0.contains_key(&Slot::from(slot_idx)))
+            .map(Slot::from)
+            .ok_or_else(|| anyhow::anyhow!("Schedule is already full"))?;
+
+        let resident_ids = self.valid_residents(slot, schedule);
+        let solved_in_thread = AtomicBool::new(false);
+
+        let solved_schedule = resident_ids.par_iter().find_map_any(|&id| {
+            let mut local_schedule = schedule.clone();
+            let mut local_tracker = tracker.clone();
+
+            local_schedule.insert(slot, id);
+            local_tracker.insert(id, &self.config, slot);
+
+            let solved = self.search(
+                &mut local_schedule,
+                &mut local_tracker,
+                slot.next(),
+                &solved_in_thread,
+            );
+            match solved {
+                Ok(true) => Some(local_schedule),
+                Ok(false) => None,
+                Err(e) => {
+                    warn!("Search error: {}", e);
+                    None
+                }
+            }
+        });
+
+        // TODO: can return the schedule instead of a bool
+
+        if let Some(solved_schedule) = solved_schedule {
+            *schedule = solved_schedule;
+            return Ok(true);
+        }
+
+        Ok(false)
     }
 
     /// DFS where maximum depth is calculated by total_days_of_month + odd_days_of_month each node is called a slot
@@ -57,7 +101,12 @@ impl Scheduler {
         schedule: &mut MonthlySchedule,
         tracker: &mut WorkloadTracker,
         slot: Slot,
+        solved_in_thread: &AtomicBool,
     ) -> anyhow::Result<bool> {
+        if solved_in_thread.load(Ordering::Relaxed) {
+            bail!("Another thread found the solution")
+        }
+
         if self.timer.limit_exceeded() {
             anyhow::bail!("Time exceeded. Restrictions too tight");
         }
@@ -69,11 +118,15 @@ impl Scheduler {
         }
 
         if slot.greater_than(self.config.total_days) {
-            return Ok(tracker.are_all_thresholds_met(&self.config, &self.bounds));
+            if tracker.are_all_thresholds_met(&self.config, &self.bounds) {
+                solved_in_thread.store(true, Ordering::Relaxed);
+                return Ok(true);
+            }
+            return Ok(false);
         }
 
         if schedule.is_slot_manually_assigned(&slot) {
-            return self.search(schedule, tracker, slot.next());
+            return self.search(schedule, tracker, slot.next(), solved_in_thread);
         }
 
         // sort candidates by current workload, add rng for tie breakers
@@ -88,7 +141,7 @@ impl Scheduler {
             schedule.insert(slot, id);
             tracker.insert(id, &self.config, slot);
 
-            if self.search(schedule, tracker, slot.next())? {
+            if self.search(schedule, tracker, slot.next(), solved_in_thread)? {
                 return Ok(true);
             }
 

src-tauri/src/slot.rs

@@ -113,6 +113,16 @@ impl Default for Slot {
     }
 }
 
+impl From<u8> for Slot {
+    fn from(value: u8) -> Self {
+        let mut slot = Slot::default();
+        for _ in 0..value {
+            slot = slot.next()
+        }
+        slot
+    }
+}
+
 #[derive(Serialize, Deserialize, PartialEq, PartialOrd, Ord, Eq, Debug, Hash, Clone, Copy)]
 #[serde(rename_all = "camelCase")]
 pub struct Day(pub u8);