refactor database engine/options; add column descriptors

Signed-off-by: Jason Volk <jason@zemos.net>

src/database/engine/context.rs

@@ -0,0 +1,73 @@
+use std::{
+	collections::BTreeMap,
+	sync::{Arc, Mutex},
+};
+
+use conduwuit::{debug, utils::math::usize_from_f64, Result, Server};
+use rocksdb::{Cache, Env};
+
+use crate::{or_else, pool::Pool};
+
+/// Some components are constructed prior to opening the database and must
+/// outlive the database. These can also be shared between database instances
+/// though at the time of this comment we only open one database per process.
+/// These assets are housed in the shared Context.
+pub(crate) struct Context {
+	pub(crate) pool: Arc<Pool>,
+	pub(crate) col_cache: Mutex<BTreeMap<String, Cache>>,
+	pub(crate) row_cache: Mutex<Cache>,
+	pub(crate) env: Mutex<Env>,
+	pub(crate) server: Arc<Server>,
+}
+
+impl Context {
+	pub(crate) fn new(server: &Arc<Server>) -> Result<Arc<Self>> {
+		let config = &server.config;
+		let cache_capacity_bytes = config.db_cache_capacity_mb * 1024.0 * 1024.0;
+
+		let row_cache_capacity_bytes = usize_from_f64(cache_capacity_bytes * 0.50)?;
+		let row_cache = Cache::new_lru_cache(row_cache_capacity_bytes);
+
+		let col_cache_capacity_bytes = usize_from_f64(cache_capacity_bytes * 0.50)?;
+		let col_cache = Cache::new_lru_cache(col_cache_capacity_bytes);
+
+		let col_cache: BTreeMap<_, _> = [("Shared".to_owned(), col_cache)].into();
+
+		let mut env = Env::new().or_else(or_else)?;
+
+		if config.rocksdb_compaction_prio_idle {
+			env.lower_thread_pool_cpu_priority();
+		}
+
+		if config.rocksdb_compaction_ioprio_idle {
+			env.lower_thread_pool_io_priority();
+		}
+
+		Ok(Arc::new(Self {
+			pool: Pool::new(server)?,
+			col_cache: col_cache.into(),
+			row_cache: row_cache.into(),
+			env: env.into(),
+			server: server.clone(),
+		}))
+	}
+}
+
+impl Drop for Context {
+	#[cold]
+	fn drop(&mut self) {
+		debug!("Closing frontend pool");
+		self.pool.close();
+
+		let mut env = self.env.lock().expect("locked");
+
+		debug!("Shutting down background threads");
+		env.set_high_priority_background_threads(0);
+		env.set_low_priority_background_threads(0);
+		env.set_bottom_priority_background_threads(0);
+		env.set_background_threads(0);
+
+		debug!("Joining background threads...");
+		env.join_all_threads();
+	}
+}