[WIP] [NOT-WORKING] Add basic cache

Author: schomatis

Diff for: storage-proofs/src/zigzag_graph.rs

@@ -1,4 +1,6 @@
 use std::marker::PhantomData;
+use std::collections::HashMap;
+use std::sync::RwLock;
 
 use crate::crypto::feistel::{self, FeistelPrecomputed};
 use crate::drgraph::{BucketGraph, Graph};
@@ -18,6 +20,7 @@ where
     base_graph: G,
     pub reversed: bool,
     feistel_precomputed: FeistelPrecomputed,
+    parents_cache: RwLock<HashMap<usize, Vec<usize>>>,
     _h: PhantomData<H>,
 }
 
@@ -50,6 +53,7 @@ where
             expansion_degree,
             reversed: false,
             feistel_precomputed: feistel::precompute((expansion_degree * nodes) as u32),
+            parents_cache: RwLock::new(HashMap::new()),
             _h: PhantomData,
         }
     }
@@ -83,6 +87,7 @@ pub trait ZigZag: ::std::fmt::Debug + Clone + PartialEq + Eq {
     fn reversed(&self) -> bool;
     fn expanded_parents(&self, node: usize) -> Vec<usize>;
     fn real_index(&self, i: usize) -> usize;
+    fn parents_cache(&self) -> RwLock<HashMap<usize, Vec<usize>>>;
     fn new_zigzag(
         nodes: usize,
         base_degree: usize,
@@ -205,6 +210,7 @@ where
             expansion_degree: self.expansion_degree,
             reversed: !self.reversed,
             feistel_precomputed: feistel::precompute((self.expansion_degree * self.size()) as u32),
+            parents_cache: RwLock::new(HashMap::new()),
             _h: PhantomData,
         }
     }
@@ -223,7 +229,13 @@ where
 
     #[inline]
     fn expanded_parents(&self, node: usize) -> Vec<usize> {
-        (0..self.expansion_degree)
+
+//        let parents_cache = self.parents_cache().read().unwrap();
+//        if (*parents_cache).contains_key(&node) {
+//            return (*parents_cache)[&node].clone();
+//        }
+
+        let parents: Vec<usize> = (0..self.expansion_degree)
             .filter_map(|i| {
                 let other = self.correspondent(node, i);
                 if self.reversed {
@@ -238,7 +250,12 @@ where
                     None
                 }
             })
-            .collect()
+            .collect();
+
+//        let mut parents_cache = self.parents_cache().write().unwrap();
+//        (*parents_cache).insert(node, parents.clone());
+
+        parents
     }
 
     #[inline]
@@ -249,6 +266,10 @@ where
             i
         }
     }
+
+    fn parents_cache(&self) -> RwLock<HashMap<usize, Vec<usize>>> {
+        self.parents_cache
+    }
 }
 
 #[cfg(test)]