Local refcounting of blocks

src/block.rs

@@ -1,49 +1,113 @@
 use std::path::PathBuf;
-use std::sync::Arc;
 
 use tokio::fs;
 use tokio::prelude::*;
+use tokio::sync::Mutex;
+use futures_util::future::*;
 
 use crate::data::*;
 use crate::error::Error;
 use crate::proto::*;
-use crate::server::Garage;
+use crate::background::*;
 
-fn block_dir(garage: &Garage, hash: &Hash) -> PathBuf {
-	let mut path = garage.system.config.data_dir.clone();
-	path.push(hex::encode(&hash.as_slice()[0..1]));
-	path.push(hex::encode(&hash.as_slice()[1..2]));
-	path
+
+pub struct BlockManager {
+	pub data_dir: PathBuf,
+	pub rc: sled::Tree,
+	pub lock: Mutex<()>,
 }
 
-pub async fn write_block(garage: Arc<Garage>, hash: &Hash, data: &[u8]) -> Result<Message, Error> {
-	garage.fs_lock.lock().await;
-
-	let mut path = block_dir(&garage, hash);
-	fs::create_dir_all(&path).await?;
-
-	path.push(hex::encode(hash));
-	if fs::metadata(&path).await.is_ok() {
-		return Ok(Message::Ok);
+impl BlockManager {
+	pub fn new(db: &sled::Db, data_dir: PathBuf) -> Self {
+		let rc = db.open_tree("block_local_rc")
+			.expect("Unable to open block_local_rc tree");
+		rc.set_merge_operator(rc_merge);
+		Self{
+			rc,
+			data_dir,
+			lock: Mutex::new(()),
+		}
 	}
 
-	let mut f = fs::File::create(path).await?;
-	f.write_all(data).await?;
-	drop(f);
+	pub async fn write_block(&self, hash: &Hash, data: &[u8]) -> Result<Message, Error> {
+		let _lock = self.lock.lock().await;
 
-	Ok(Message::Ok)
+		let mut path = self.block_dir(hash);
+		fs::create_dir_all(&path).await?;
+
+		path.push(hex::encode(hash));
+		if fs::metadata(&path).await.is_ok() {
+			return Ok(Message::Ok);
+		}
+
+		let mut f = fs::File::create(path).await?;
+		f.write_all(data).await?;
+		drop(f);
+
+		Ok(Message::Ok)
+	}
+
+	pub async fn read_block(&self, hash: &Hash) -> Result<Message, Error> {
+		let mut path = self.block_dir(hash);
+		path.push(hex::encode(hash));
+
+		let mut f = fs::File::open(path).await?;
+		let mut data = vec![];
+		f.read_to_end(&mut data).await?;
+
+		Ok(Message::PutBlock(PutBlockMessage {
+			hash: hash.clone(),
+			data,
+		}))
+	}
+
+	fn block_dir(&self, hash: &Hash) -> PathBuf {
+		let mut path = self.data_dir.clone();
+		path.push(hex::encode(&hash.as_slice()[0..1]));
+		path.push(hex::encode(&hash.as_slice()[1..2]));
+		path
+	}
+
+	pub fn block_incref(&self, hash: &Hash) -> Result<(), Error> {
+		self.rc.merge(&hash, vec![1])?;
+		Ok(())
+	}
+
+	pub fn block_decref(&self, hash: &Hash, background: &BackgroundRunner) -> Result<(), Error> {
+		match self.rc.merge(&hash, vec![0])? {
+			None => {
+				let mut path = self.block_dir(hash);
+				path.push(hex::encode(hash));
+				background.spawn(tokio::fs::remove_file(path).map_err(Into::into));
+				Ok(())
+			}
+			Some(_) => Ok(())
+		}
+	}
 }
 
-pub async fn read_block(garage: Arc<Garage>, hash: &Hash) -> Result<Message, Error> {
-	let mut path = block_dir(&garage, hash);
-	path.push(hex::encode(hash));
-
-	let mut f = fs::File::open(path).await?;
-	let mut data = vec![];
-	f.read_to_end(&mut data).await?;
-
-	Ok(Message::PutBlock(PutBlockMessage {
-		hash: hash.clone(),
-		data,
-	}))
+fn rc_merge(_key: &[u8], old: Option<&[u8]>, new: &[u8]) -> Option<Vec<u8>> {
+	let old = old.map(|x| {
+		assert!(x.len() == 8);
+		let mut x8 = [0u8; 8];
+		x8.copy_from_slice(x);
+		u64::from_be_bytes(x8)
+	}).unwrap_or(0);
+	assert!(new.len() == 1);
+	let new = match new[0] {
+		0 => {
+			if old > 0 {
+				old - 1
+			} else {
+				0
+			}
+		}
+		1 => old + 1,
+		_ => unreachable!(),
+	};
+	if new == 0 {
+		None
+	} else {
+		Some(u64::to_be_bytes(new).to_vec())
+	}
 }