diff --git a/Cargo.toml b/Cargo.toml
index 3d7d4da..9c9f4a4 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -7,13 +7,16 @@ edition = "2024"
 members = ["macros", "utils"]
 
 [features]
-default = ["tokio"]
+default = []
 cli = [
     "tokio/rt-multi-thread",
     "dep:clap",
-    "dep:figment",
     "dep:color-eyre",
     "dep:num_cpus",
+    "figment/yaml",
+    "figment/json",
+    "figment/toml",
+    "figment/env"
 ]
 tokio = ["dep:tokio"]
 # Very long running.
@@ -53,7 +56,7 @@ blake3 = "1.8.2"
 slotmap = { version = "1.0.7", features = ["serde"] }
 
 clap = { version = "4.5.47", features = ["derive"], optional = true }
-figment = { version = "0.10.19", features = ["json", "yaml", "env", "toml"], optional = true }
+figment = { version = "0.10.19" }
 tokio = { version = "1.47.1", features = ["rt", "sync", "macros"], optional = true }
 color-eyre = { version = "0.6.5", optional = true }
 eyre = { version = "0.6.12" }
diff --git a/src/cli/mod.rs b/src/cli/mod.rs
index 4e08f49..001b618 100644
--- a/src/cli/mod.rs
+++ b/src/cli/mod.rs
@@ -1,4 +1,9 @@
-use std::{num::NonZeroUsize, path::PathBuf};
+use std::{
+    any::{TypeId, type_name},
+    num::NonZeroUsize,
+    path::PathBuf,
+    sync::{Arc, Mutex},
+};
 
 use clap::{Args, Parser};
 
@@ -7,24 +12,39 @@ use figment::{
     Figment,
     providers::{Env, Format, Json, Toml, YamlExtended},
 };
+use hashbrown::hash_map;
 
-use tokio::runtime as rt;
+use crate::{collections::HashMap, str::CompactString};
+
+use crate::component_configs::{
+    ComponentConfigs, ConfigHandle, DeserializeCfg, ErasedValue, IsComponentConfig,
+};
+
+use tokio::runtime;
+
+pub mod rt;
+
+#[derive(Debug, Clone, Copy, clap::Args)]
+pub struct NoArgs {}
 
 #[derive(Parser)]
 struct AppArgs<A: Args> {
     #[clap(long, short)]
     /// Config file(s) for the application.
     config: Vec<PathBuf>,
-    #[clap(long, short)]
-    /// Number of worker threads app will consume.
-    worker_threads: Option<NonZeroUsize>,
 
     #[clap(flatten)]
     args: A,
 }
 
+struct ComponentConfigSetup {
+    section: CompactString,
+    deserialize: DeserializeCfg,
+}
+
 pub struct App {
     figment: Figment,
+    component_configs: HashMap<TypeId, ComponentConfigSetup>,
 }
 
 impl App {
@@ -34,19 +54,70 @@ impl App {
         self
     }
 
-    pub fn run<A, C>(
+    pub fn optional<T: IsComponentConfig + Default>(mut self, section: &str) -> Self {
+        let hash_map::Entry::Vacant(vacant) = self.component_configs.entry(TypeId::of::<T>())
+        else {
+            panic!("{} already exists", type_name::<T>())
+        };
+
+        vacant.insert(ComponentConfigSetup {
+            section: section.into(),
+            deserialize: |path, figment| {
+                let res: figment::Result<T> = figment.extract_inner_lossy(path);
+                let res = match res {
+                    Ok(o) => Ok(o),
+                    Err(e) => match &e.kind {
+                        figment::error::Kind::MissingField(field) if field == path => {
+                            Ok(T::default())
+                        }
+                        _ => Err(e).wrap_err("failed to deserialize section"),
+                    },
+                };
+
+                res.map(|x| {
+                    let x: ErasedValue = Arc::new(Mutex::new(x));
+                    x
+                })
+            },
+        });
+
+        self
+    }
+
+    pub fn require<T: IsComponentConfig>(mut self, section: &str) -> Self {
+        let hash_map::Entry::Vacant(vacant) = self.component_configs.entry(TypeId::of::<T>())
+        else {
+            panic!("{} already exists", type_name::<T>())
+        };
+
+        vacant.insert(ComponentConfigSetup {
+            section: section.into(),
+            deserialize: |path, figment| {
+                let res: T = figment
+                    .extract_inner_lossy(path)
+                    .wrap_err("failed to deserialize")?;
+                Ok(Arc::new(Mutex::new(res)))
+            },
+        });
+        self
+    }
+
+    pub fn run<A>(
         self,
-        f: impl Send + 'static + AsyncFnOnce(A, C) -> eyre::Result<()>,
+        f: impl Send + 'static + AsyncFnOnce(A, ComponentConfigs) -> eyre::Result<()>,
     ) -> eyre::Result<()>
     where
         A: Args,
-        C: serde::de::DeserializeOwned,
     {
-        let Self { mut figment } = self;
+        const ONE: NonZeroUsize = NonZeroUsize::new(1).unwrap();
+
+        let Self {
+            mut figment,
+            component_configs,
+        } = self;
         color_eyre::install().wrap_err("failed to install color-eyre")?;
         let AppArgs {
             config: configs,
-            worker_threads,
             args,
         } = AppArgs::<A>::parse();
 
@@ -55,7 +126,10 @@ impl App {
             let component = config.components().next_back().ok_or_else(|| {
                 eyre::eyre!("{} must contain at least one component", config.display())
             })?;
-            let last = component.as_os_str().as_encoded_bytes();
+            let last = component
+                .as_os_str()
+                .as_encoded_bytes()
+                .to_ascii_lowercase();
 
             if config.is_dir() {
                 todo!("populate everything from the directory")
@@ -68,12 +142,27 @@ impl App {
             }
         }
 
-        let config: C = figment.extract_lossy().wrap_err("failed to load config")?;
-        let rt = match worker_threads.map_or(num_cpus::get(), NonZeroUsize::get) {
-            0 | 1 => rt::Builder::new_current_thread(),
-            n => {
-                let mut b = rt::Builder::new_multi_thread();
-                b.worker_threads(n);
+        let mut map = HashMap::default();
+        for (type_id, setup) in component_configs {
+            let handle = ConfigHandle::initial(setup.section, setup.deserialize, &figment)?;
+            map.insert(type_id, Arc::new(handle));
+        }
+
+        let component_configs = ComponentConfigs::new(map);
+        let rt_config = component_configs.get::<rt::RtConfig>();
+
+        let rt = match rt_config.flavor {
+            rt::Flavor::MultiThreaded {
+                threads: rt::ThreadsCount::Specific(ONE),
+            }
+            | rt::Flavor::SingleThreaded => runtime::Builder::new_current_thread(),
+            rt::Flavor::MultiThreaded { threads } => {
+                let mut b = runtime::Builder::new_current_thread();
+                b.worker_threads(match threads {
+                    rt::ThreadsCount::Specific(s) => s.get(),
+                    rt::ThreadsCount::ThreadPerCpu => num_cpus::get(),
+                });
+
                 b
             }
         }
@@ -81,14 +170,19 @@ impl App {
         .build()
         .wrap_err("failed to create tokio runtime")?;
 
-        rt.block_on(f(args, config))
+        drop(rt_config);
+
+        rt.block_on(f(args, component_configs))
     }
 }
 
 impl Default for App {
     fn default() -> Self {
-        Self {
+        let this = Self {
+            component_configs: HashMap::default(),
             figment: Figment::new(),
-        }
+        };
+
+        this.optional::<rt::RtConfig>("system.rt")
     }
 }
diff --git a/src/cli/rt.rs b/src/cli/rt.rs
new file mode 100644
index 0000000..edac716
--- /dev/null
+++ b/src/cli/rt.rs
@@ -0,0 +1,37 @@
+use std::num::NonZeroUsize;
+
+use crate::data;
+
+#[data(crate = crate)]
+#[derive(Default)]
+#[serde(default)]
+pub struct RtConfig {
+    pub flavor: Flavor,
+}
+
+#[data(crate = crate, copy)]
+#[derive(Default)]
+pub enum ThreadsCount {
+    #[default]
+    ThreadPerCpu,
+    #[serde(untagged)]
+    Specific(NonZeroUsize),
+}
+
+#[data(crate = crate, copy)]
+pub enum Flavor {
+    SingleThreaded,
+    #[serde(rename = "worker_threads")]
+    MultiThreaded {
+        #[serde(default)]
+        threads: ThreadsCount,
+    },
+}
+
+impl Default for Flavor {
+    fn default() -> Self {
+        Self::MultiThreaded {
+            threads: ThreadsCount::default(),
+        }
+    }
+}
diff --git a/src/component_configs.rs b/src/component_configs.rs
new file mode 100644
index 0000000..66fde80
--- /dev/null
+++ b/src/component_configs.rs
@@ -0,0 +1,124 @@
+use crate::{collections::HashMap, str::CompactString, trait_set};
+
+use std::{
+    mem,
+    any::{Any, TypeId},
+    ops::Deref,
+    sync::{
+        Arc, Mutex,
+        atomic::{AtomicUsize, Ordering},
+    },
+};
+
+use eyre::Context;
+use figment::Figment;
+
+pub(crate) type ErasedValue = Arc<Mutex<dyn Send + Sync + Any + 'static>>;
+pub(crate) type DeserializeCfg = fn(&str, &Figment) -> eyre::Result<ErasedValue>;
+
+trait_set! {
+    pub trait IsComponentConfig = Any + 'static + Clone + Send + Sync + serde::de::DeserializeOwned + serde::Serialize;
+}
+
+pub(crate) struct ConfigHandle {
+    section: CompactString,
+    recent: ErasedValue,
+    generation: AtomicUsize,
+    deserialize: DeserializeCfg,
+}
+
+impl ConfigHandle {
+    pub(crate) fn initial(
+        section: CompactString,
+        deserialize: DeserializeCfg,
+        figment: &Figment,
+    ) -> eyre::Result<Self> {
+        let recent =
+            deserialize(&section, figment).wrap_err("failed to deserialize config at start")?;
+
+        Ok(Self {
+            section,
+            recent,
+            deserialize,
+            generation: AtomicUsize::new(0),
+        })
+    }
+
+    pub(crate) fn read<T: IsComponentConfig>(&self) -> Option<(T, usize)> {
+        let cfg = self.recent.lock().unwrap();
+        let generation = self.generation.load(Ordering::Relaxed);
+
+        cfg.downcast_ref::<T>().map(|r| (r.clone(), generation))
+    }
+}
+
+#[derive(Clone)]
+pub struct ComponentConfigs {
+    map: Arc<HashMap<TypeId, Arc<ConfigHandle>>>,
+}
+
+impl ComponentConfigs {
+    pub(crate) fn new(map: HashMap<TypeId, Arc<ConfigHandle>>) -> Self {
+        Self { map: Arc::new(map) }
+    }
+
+    #[track_caller]
+    pub fn get<T: IsComponentConfig>(&self) -> ComponentConfig<T> {
+        self.try_get::<T>().unwrap_or_else(|| {
+            panic!(
+                "configuration for {} does not exist",
+                std::any::type_name::<T>()
+            )
+        })
+    }
+
+    pub fn try_get<T: IsComponentConfig>(&self) -> Option<ComponentConfig<T>> {
+        let type_id = TypeId::of::<T>();
+        self.map.get(&type_id).cloned().map(|handle| {
+            let (cfg, generation) = handle.read::<T>().unwrap();
+            ComponentConfig {
+                cfg,
+                generation,
+                handle,
+            }
+        })
+    }
+}
+
+pub struct ComponentConfig<T> {
+    cfg: T,
+    generation: usize,
+    handle: Arc<ConfigHandle>,
+}
+
+impl<T: IsComponentConfig> ComponentConfig<T> {
+    pub fn section(&self) -> &str {
+        &self.handle.section
+    }
+
+    /// Update component config. Returns previous config if something's changed.
+    pub fn try_update(&mut self) -> Option<T> {
+        let generation = self.handle.generation.load(Ordering::Relaxed);
+
+        if generation == self.generation {
+            None
+        } else {
+            Some(self.force_update())
+        }
+    }
+
+    /// Update component config forcibly.
+    pub fn force_update(&mut self) -> T {
+        let (cfg, generation) = self.handle.read::<T>().unwrap();
+        self.generation = generation;
+        mem::replace(&mut self.cfg, cfg)
+    }
+}
+
+impl<T> Deref for ComponentConfig<T> {
+    type Target = T;
+
+    fn deref(&self) -> &Self::Target {
+        &self.cfg
+    }
+}
diff --git a/src/lib.rs b/src/lib.rs
index 8ad8a4e..81ef92e 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -48,6 +48,9 @@ pub mod collections;
 pub mod handling;
 pub mod hash;
 
+pub mod component_configs;
+pub mod signal;
+
 pub use either::{self, Either, Left, Right};
 pub use paste::paste;
 
diff --git a/src/signal.rs b/src/signal.rs
new file mode 100644
index 0000000..d1311d1
--- /dev/null
+++ b/src/signal.rs
@@ -0,0 +1,7 @@
+use crate::data;
+
+#[data(crate = crate, copy)]
+pub enum Signal {
+    /// SIGHUP.
+    HangUp,
+}
diff --git a/src/supervisor/mod.rs b/src/supervisor/mod.rs
index 62841fd..30c3bee 100644
--- a/src/supervisor/mod.rs
+++ b/src/supervisor/mod.rs
@@ -1,8 +1,10 @@
+use compact_str::ToCompactString;
 use eyre::eyre;
 use tokio::{sync::mpsc, task::JoinSet};
 
 use crate::{
     collections::{HashMap, hash_map},
+    component_configs::{ComponentConfig, ComponentConfigs, IsComponentConfig},
     data,
     fut::Fut,
     str::CompactString,
@@ -65,29 +67,49 @@ impl Handle {
     }
 }
 
-#[derive(Default)]
+pub trait Supervised<T>:
+    Send + Sync + 'static + Fn(ComponentConfig<T>, SlaveRx) -> Self::Fut
+{
+    type Fut: 'static + Fut<Output = eyre::Result<()>>;
+}
+
+impl<T, F, FFut> Supervised<T> for F
+where
+    F: Send + Sync + 'static + Fn(ComponentConfig<T>, SlaveRx) -> FFut,
+    FFut: 'static + Fut<Output = eyre::Result<()>>,
+{
+    type Fut = FFut;
+}
+
 pub struct Supervisor {
     set: JoinSet<eyre::Result<()>>,
     handles: HashMap<CompactString, Handle>,
+    configs: ComponentConfigs,
 }
 
 impl Supervisor {
-    pub fn empty() -> Self {
-        Self::default()
+    pub fn new(configs: ComponentConfigs) -> Self {
+        Self {
+            set: JoinSet::new(),
+            handles: HashMap::default(),
+            configs,
+        }
     }
 
-    pub fn add<F, FFut>(mut self, name: &str, f: F) -> Self
+    pub fn add<T>(mut self, f: impl Supervised<T>) -> Self
     where
-        F: Send + 'static + FnOnce(SlaveRx) -> FFut,
-        FFut: 'static + Fut<Output = eyre::Result<()>>,
+        T: IsComponentConfig,
     {
         let (tx, mut rx) = mpsc::channel(8);
         let (stx, srx) = mpsc::channel(8);
         let handle = Handle { tx };
         let slave_rx = SlaveRx { rx: srx };
 
+        let config = self.configs.get::<T>();
+        let name = config.section().to_compact_string();
+
         self.set.spawn(async move {
-            let fut = f(slave_rx);
+            let fut = f(config, slave_rx);
             tokio::pin!(fut);
             loop {
                 tokio::select! {
@@ -116,7 +138,7 @@ impl Supervisor {
             }
         });
 
-        let hash_map::Entry::Vacant(vac) = self.handles.entry(name.into()) else {
+        let hash_map::Entry::Vacant(vac) = self.handles.entry(name.clone()) else {
             panic!("{name:?} already exists")
         };
 
diff --git a/utils/src/sync/sema.rs b/utils/src/sync/sema.rs
new file mode 100644
index 0000000..e69de29