Reset historian's hasher between events

Hasher will generate different hashes for the same input if it
had already generated a hash.

Also add a binary to ensure the example in the README works.

src/bin/demo.rs

@@ -0,0 +1,28 @@
+extern crate silk;
+
+use silk::historian::Historian;
+use silk::log::{verify_slice, Entry, Event};
+use std::{thread, time};
+
+fn create_log(hist: &Historian) -> Vec<Entry> {
+    hist.sender.send(Event::Tick).unwrap();
+    thread::sleep(time::Duration::new(0, 100_000));
+    hist.sender.send(Event::UserDataKey(0xdeadbeef)).unwrap();
+    thread::sleep(time::Duration::new(0, 100_000));
+    hist.sender.send(Event::Tick).unwrap();
+
+    let entry0 = hist.receiver.recv().unwrap();
+    let entry1 = hist.receiver.recv().unwrap();
+    let entry2 = hist.receiver.recv().unwrap();
+    vec![entry0, entry1, entry2]
+}
+
+fn main() {
+    let seed = 0;
+    let hist = Historian::new(seed);
+    let entries = create_log(&hist);
+    for entry in &entries {
+        println!("{:?}", entry);
+    }
+    assert!(verify_slice(&entries, seed));
+}

src/historian.rs

@@ -73,7 +73,11 @@ pub fn create_logger(
         let mut num_hashes = 0;
         loop {
             match log_events(&receiver, &sender, num_hashes, end_hash) {
-                Ok(n) => num_hashes = n,
+                Ok(0) => {
+                    num_hashes = 0;
+                    hasher = DefaultHasher::new();
+                }
+                Ok(_) => {}
                 Err(err) => return err,
             }
             end_hash.hash(&mut hasher);
@@ -104,17 +108,22 @@ mod tests {
 
     #[test]
     fn test_historian() {
+        use std::thread::sleep;
+        use std::time::Duration;
+
         let hist = Historian::new(0);
 
-        let event = Event::Tick;
-        hist.sender.send(event.clone()).unwrap();
-        let entry0 = hist.receiver.recv().unwrap();
-        assert_eq!(entry0.event, event);
+        hist.sender.send(Event::Tick).unwrap();
+        sleep(Duration::new(0, 100_000));
+        hist.sender.send(Event::UserDataKey(0xdeadbeef)).unwrap();
+        sleep(Duration::new(0, 100_000));
+        hist.sender.send(Event::Tick).unwrap();
 
-        let event = Event::UserDataKey(0xdeadbeef);
-        hist.sender.send(event.clone()).unwrap();
+        let entry0 = hist.receiver.recv().unwrap();
         let entry1 = hist.receiver.recv().unwrap();
-        assert_eq!(entry1.event, event);
+        let entry2 = hist.receiver.recv().unwrap();
+        assert!(entry1.num_hashes != 0);
+        assert!(entry2.num_hashes != 0);
 
         drop(hist.sender);
         assert_eq!(
@@ -122,7 +131,7 @@ mod tests {
             ExitReason::RecvDisconnected
         );
 
-        assert!(verify_slice(&[entry0, entry1], 0));
+        assert!(verify_slice(&[entry0, entry1, entry2], 0));
     }
 
     #[test]