From 26dde26c48825567ce6c74c57d353a31b7cc2ab0 Mon Sep 17 00:00:00 2001
From: Paul Hauner <paul@paulhauner.com>
Date: Wed, 8 Jan 2020 11:09:27 +1100
Subject: [PATCH] Use Cow for checkpoint cache (#775)

---
 beacon_node/beacon_chain/src/beacon_chain.rs     | 7 ++++---
 beacon_node/beacon_chain/src/checkpoint_cache.rs | 7 ++++---
 2 files changed, 8 insertions(+), 6 deletions(-)

diff --git a/beacon_node/beacon_chain/src/beacon_chain.rs b/beacon_node/beacon_chain/src/beacon_chain.rs
index 59d2ceb6e9..c5df4fe83e 100644
--- a/beacon_node/beacon_chain/src/beacon_chain.rs
+++ b/beacon_node/beacon_chain/src/beacon_chain.rs
@@ -23,6 +23,7 @@ use state_processing::per_block_processing::{
 use state_processing::{
     per_block_processing, per_slot_processing, BlockProcessingError, BlockSignatureStrategy,
 };
+use std::borrow::Cow;
 use std::fs;
 use std::io::prelude::*;
 use std::sync::Arc;
@@ -1411,12 +1412,12 @@ impl<T: BeaconChainTypes> BeaconChain<T> {
         //
         // A block that was just imported is likely to be referenced by the next block that we
         // import.
-        self.checkpoint_cache.insert(&CheckPoint {
+        self.checkpoint_cache.insert(Cow::Owned(CheckPoint {
             beacon_block_root: block_root,
             beacon_block: block,
             beacon_state_root: state_root,
             beacon_state: state,
-        });
+        }));
 
         metrics::stop_timer(full_timer);
 
@@ -1626,7 +1627,7 @@ impl<T: BeaconChainTypes> BeaconChain<T> {
                 // Store the head in the checkpoint cache.
                 //
                 // The head block is likely to be referenced by the next imported block.
-                self.checkpoint_cache.insert(&new_head);
+                self.checkpoint_cache.insert(Cow::Borrowed(&new_head));
 
                 // Update the checkpoint that stores the head of the chain at the time it received the
                 // block.
diff --git a/beacon_node/beacon_chain/src/checkpoint_cache.rs b/beacon_node/beacon_chain/src/checkpoint_cache.rs
index 73e9746ae9..3832182e9b 100644
--- a/beacon_node/beacon_chain/src/checkpoint_cache.rs
+++ b/beacon_node/beacon_chain/src/checkpoint_cache.rs
@@ -1,6 +1,7 @@
 use crate::checkpoint::CheckPoint;
 use crate::metrics;
 use parking_lot::RwLock;
+use std::borrow::Cow;
 use types::{BeaconBlock, BeaconState, EthSpec, Hash256};
 
 const CACHE_SIZE: usize = 4;
@@ -34,7 +35,7 @@ impl<T: EthSpec> Default for CheckPointCache<T> {
 }
 
 impl<T: EthSpec> CheckPointCache<T> {
-    pub fn insert(&self, checkpoint: &CheckPoint<T>) {
+    pub fn insert(&self, checkpoint: Cow<CheckPoint<T>>) {
         if self
             .inner
             .read()
@@ -50,10 +51,10 @@ impl<T: EthSpec> CheckPointCache<T> {
         let mut inner = self.inner.write();
 
         if inner.checkpoints.len() < inner.limit {
-            inner.checkpoints.push(checkpoint.clone())
+            inner.checkpoints.push(checkpoint.into_owned())
         } else {
             let i = inner.oldest; // to satisfy the borrow checker.
-            inner.checkpoints[i] = checkpoint.clone();
+            inner.checkpoints[i] = checkpoint.into_owned();
             inner.oldest += 1;
             inner.oldest %= inner.limit;
         }