Merge pull request #165 from rlkelly/126__atomic_balances

126  atomic balances

src/accountant.rs

@@ -15,6 +15,7 @@ use signature::{KeyPair, PublicKey, Signature};
 use std::collections::hash_map::Entry::Occupied;
 use std::collections::{HashMap, HashSet, VecDeque};
 use std::result;
+use std::sync::atomic::{AtomicIsize, Ordering};
 use std::sync::RwLock;
 use transaction::Transaction;
 
@@ -30,18 +31,18 @@ pub enum AccountingError {
 pub type Result<T> = result::Result<T, AccountingError>;
 
 /// Commit funds to the 'to' party.
-fn apply_payment(balances: &RwLock<HashMap<PublicKey, RwLock<i64>>>, payment: &Payment) {
+fn apply_payment(balances: &RwLock<HashMap<PublicKey, AtomicIsize>>, payment: &Payment) {
     if balances.read().unwrap().contains_key(&payment.to) {
         let bals = balances.read().unwrap();
-        *bals[&payment.to].write().unwrap() += payment.tokens;
+        bals[&payment.to].fetch_add(payment.tokens as isize, Ordering::Relaxed);
     } else {
         let mut bals = balances.write().unwrap();
-        bals.insert(payment.to, RwLock::new(payment.tokens));
+        bals.insert(payment.to, AtomicIsize::new(payment.tokens as isize));
     }
 }
 
 pub struct Accountant {
-    balances: RwLock<HashMap<PublicKey, RwLock<i64>>>,
+    balances: RwLock<HashMap<PublicKey, AtomicIsize>>,
     pending: RwLock<HashMap<Signature, Plan>>,
     last_ids: RwLock<VecDeque<(Hash, RwLock<HashSet<Signature>>)>>,
     time_sources: RwLock<HashSet<PublicKey>>,
@@ -127,27 +128,37 @@ impl Accountant {
     /// funds and isn't a duplicate.
     pub fn process_verified_transaction_debits(&self, tr: &Transaction) -> Result<()> {
         let bals = self.balances.read().unwrap();
-
-        // Hold a write lock before the condition check, so that a debit can't occur
-        // between checking the balance and the withdraw.
         let option = bals.get(&tr.from);
+
         if option.is_none() {
             return Err(AccountingError::AccountNotFound);
         }
-        let mut bal = option.unwrap().write().unwrap();
 
         if !self.reserve_signature_with_last_id(&tr.sig, &tr.data.last_id) {
             return Err(AccountingError::InvalidTransferSignature);
         }
 
-        if *bal < tr.data.tokens {
-            self.forget_signature_with_last_id(&tr.sig, &tr.data.last_id);
-            return Err(AccountingError::InsufficientFunds);
+        loop {
+            let bal = option.unwrap();
+            let current = bal.load(Ordering::Relaxed) as i64;
+
+            if current < tr.data.tokens {
+                self.forget_signature_with_last_id(&tr.sig, &tr.data.last_id);
+                return Err(AccountingError::InsufficientFunds);
+            }
+
+            let result = bal.compare_exchange(
+                current as isize,
+                (current - tr.data.tokens) as isize,
+                Ordering::Relaxed,
+                Ordering::Relaxed,
+            );
+
+            match result {
+                Ok(_) => return Ok(()),
+                Err(_) => continue,
+            };
         }
-
-        *bal -= tr.data.tokens;
-
-        Ok(())
     }
 
     pub fn process_verified_transaction_credits(&self, tr: &Transaction) {
@@ -300,7 +311,7 @@ impl Accountant {
 
     pub fn get_balance(&self, pubkey: &PublicKey) -> Option<i64> {
         let bals = self.balances.read().unwrap();
-        bals.get(pubkey).map(|x| *x.read().unwrap())
+        bals.get(pubkey).map(|x| x.load(Ordering::Relaxed) as i64)
     }
 }
 

src/accountant_skel.rs

@@ -487,14 +487,14 @@ mod tests {
     use std::time::Duration;
     use transaction::Transaction;
 
-    use subscribers::{Node, Subscribers};
-    use streamer;
-    use std::sync::mpsc::channel;
-    use std::collections::VecDeque;
-    use hash::{hash, Hash};
-    use event::Event;
-    use entry;
     use chrono::prelude::*;
+    use entry;
+    use event::Event;
+    use hash::{hash, Hash};
+    use std::collections::VecDeque;
+    use std::sync::mpsc::channel;
+    use streamer;
+    use subscribers::{Node, Subscribers};
 
     #[test]
     fn test_layout() {

src/packet.rs

@@ -4,9 +4,9 @@ use result::{Error, Result};
 use std::collections::VecDeque;
 use std::fmt;
 use std::io;
+use std::mem::size_of;
 use std::net::{IpAddr, Ipv4Addr, Ipv6Addr, SocketAddr, UdpSocket};
 use std::sync::{Arc, Mutex, RwLock};
-use std::mem::size_of;
 
 pub type SharedPackets = Arc<RwLock<Packets>>;
 pub type SharedBlob = Arc<RwLock<Blob>>;

src/result.rs

@@ -1,10 +1,10 @@
 //! The `result` module exposes a Result type that propagates one of many different Error types.
 
+use accountant;
 use bincode;
 use serde_json;
 use std;
 use std::any::Any;
-use accountant;
 
 #[derive(Debug)]
 pub enum Error {

src/streamer.rs

@@ -382,8 +382,9 @@ mod test {
     use std::sync::mpsc::channel;
     use std::sync::{Arc, RwLock};
     use std::time::Duration;
-    use streamer::{blob_receiver, receiver, responder, retransmitter, window, BlobReceiver,
-                   PacketReceiver};
+    use streamer::{
+        blob_receiver, receiver, responder, retransmitter, window, BlobReceiver, PacketReceiver,
+    };
     use subscribers::{Node, Subscribers};
 
     fn get_msgs(r: PacketReceiver, num: &mut usize) {