From 67286901091f75dcfaf5b5de0030d215b05ccec6 Mon Sep 17 00:00:00 2001
From: arkpar <arkady.paronyan@gmail.com>
Date: Thu, 21 Jan 2016 23:34:06 +0100
Subject: [PATCH] DB commit queue

---
 src/db_queue.rs | 111 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 111 insertions(+)
 create mode 100644 src/db_queue.rs

diff --git a/src/db_queue.rs b/src/db_queue.rs
new file mode 100644
index 000000000..242fd9cc4
--- /dev/null
+++ b/src/db_queue.rs
@@ -0,0 +1,111 @@
+//! A queue of state changes that are written to database in background.
+use std::thread::{JoinHandle, self};
+use std::sync::atomic::{AtomicBool, Ordering as AtomicOrdering};
+use util::*;
+use engine::Engine;
+use client::Client;
+
+/// State DB commit params
+pub struct StateDBCommit {
+	/// Database to commit
+	pub db: JournalDB,
+	/// Starting block number
+	pub now: u64,
+	/// Block ahash
+	pub hash: H256,
+	/// End block number + hash
+	pub end: Option<(u64, H256)>,
+}
+
+/// A queue of state changes that are written to database in background.
+pub struct DbQueue {
+	more_to_write: Arc<Condvar>,
+	queue: Arc<Mutex<VecDeque<StateDBCommit>>>,
+	writer: Mutex<Option<JoinHandle<()>>>,
+	deleting: Arc<AtomicBool>,
+}
+
+impl DbQueue {
+	/// Creates a new queue instance.
+	pub fn new() -> DbQueue {
+		let queue = Arc::new(Mutex::new(VecDeque::new()));
+		let more_to_write = Arc::new(Condvar::new());
+		let deleting = Arc::new(AtomicBool::new(false));
+
+		DbQueue {
+			more_to_write: more_to_write.clone(),
+			queue: queue.clone(),
+			writer: Mutex::new(None),
+			deleting: deleting.clone(),
+		}
+	}
+
+	/// Start processing the queue
+	pub fn start(&self, client: Weak<Client>) {
+		let writer = {
+			let queue = self.queue.clone();
+			let client = client.clone();
+			let more_to_write = self.more_to_write.clone();
+			let deleting = self.deleting.clone();
+			thread::Builder::new().name("DB Writer".to_string()).spawn(move || DbQueue::writer_loop(client, queue, more_to_write, deleting)).expect("Error creating db writer thread")
+		};
+		mem::replace(self.writer.lock().unwrap().deref_mut(), Some(writer));
+	}
+
+	fn writer_loop(client: Weak<Client>, queue: Arc<Mutex<VecDeque<StateDBCommit>>>, wait: Arc<Condvar>, deleting: Arc<AtomicBool>) {
+		while !deleting.load(AtomicOrdering::Relaxed) {
+			let mut batch = {
+				let mut locked = queue.lock().unwrap();
+				while locked.is_empty() && !deleting.load(AtomicOrdering::Relaxed) {
+					locked = wait.wait(locked).unwrap();
+				}
+				
+				if deleting.load(AtomicOrdering::Relaxed) {
+					return;
+				}
+				mem::replace(locked.deref_mut(), VecDeque::new())
+			};
+
+			for mut state in batch.drain(..) { //TODO: make this a single write transaction
+				match state.db.commit(state.now, &state.hash, state.end.clone()) {
+					Ok(_) => (),
+					Err(e) => {
+						warn!(target: "client", "State DB commit failed: {:?}", e);
+					}
+				}
+				client.upgrade().unwrap().clear_state(&state.hash);
+			}
+
+		}
+	}
+
+	/// Add a state to the queue
+	pub fn queue(&self, state: StateDBCommit) {
+		let mut queue = self.queue.lock().unwrap();
+		queue.push_back(state);
+		self.more_to_write.notify_all();
+	}
+}
+
+impl Drop for DbQueue {
+	fn drop(&mut self) {
+		self.deleting.store(true, AtomicOrdering::Relaxed);
+		self.more_to_write.notify_all();
+		mem::replace(self.writer.lock().unwrap().deref_mut(), None).unwrap().join().unwrap();
+	}
+}
+
+#[cfg(test)]
+mod tests {
+	use util::*;
+	use spec::*;
+	use queue::*;
+
+	#[test]
+	fn test_block_queue() {
+		// TODO better test
+		let spec = Spec::new_test();
+		let engine = spec.to_engine().unwrap();
+		let _ = BlockQueue::new(Arc::new(engine), IoChannel::disconnected());
+	}
+}