Make the sync module release memory aggressively

Shrink HashMaps and Vectors of downloaders and Verification queue
to reduce the memory usage when syncing.

Author: HoOngEe

core/src/verification/queue/mod.rs

@@ -408,6 +408,7 @@ impl<K: Kind> VerificationQueue<K> {
                 *td -= score;
             }
         }
+        processing.shrink_to_fit();
         processing.is_empty()
     }
 
@@ -429,6 +430,7 @@ impl<K: Kind> VerificationQueue<K> {
                 *td -= score;
             }
         }
+        processing.shrink_to_fit();
 
         let mut new_verified = VecDeque::new();
         let mut removed_size = 0;
@@ -444,6 +446,7 @@ impl<K: Kind> VerificationQueue<K> {
                 new_verified.push_back(output);
             }
         }
+        processing.shrink_to_fit();
 
         self.verification.sizes.verified.fetch_sub(removed_size, AtomicOrdering::SeqCst);
         *verified = new_verified;

sync/src/block/downloader/body.rs

@@ -69,6 +69,7 @@ impl BodyDownloader {
                 self.downloaded.insert(hash, body);
             }
         }
+        self.downloading.shrink_to_fit();
     }
 
     pub fn add_target(&mut self, header: &Header, parent: &Header) {
@@ -93,13 +94,17 @@ impl BodyDownloader {
             self.downloading.remove(hash);
             self.downloaded.remove(hash);
         }
+        self.targets.shrink_to_fit();
+        self.downloading.shrink_to_fit();
+        self.downloaded.shrink_to_fit();
     }
 
     pub fn reset_downloading(&mut self, hashes: &[H256]) {
         cdebug!(SYNC, "Remove downloading by timeout {:?}", hashes);
         for hash in hashes {
             self.downloading.remove(&hash);
         }
+        self.downloading.shrink_to_fit();
     }
 
     pub fn drain(&mut self) -> Vec<(H256, Vec<UnverifiedTransaction>)> {
@@ -111,7 +116,9 @@ impl BodyDownloader {
                 break
             }
         }
+        self.downloaded.shrink_to_fit();
         self.targets.drain(0..result.len());
+        self.targets.shrink_to_fit();
         result
     }
 }

sync/src/block/downloader/header.rs

@@ -187,6 +187,7 @@ impl HeaderDownloader {
                 }
             }
         }
+        self.queued.shrink_to_fit();
     }
 
     pub fn mark_as_queued(&mut self, hashes: Vec<H256>) {
@@ -195,5 +196,6 @@ impl HeaderDownloader {
                 self.queued.insert(hash, header);
             }
         }
+        self.downloaded.shrink_to_fit();
     }
 }