1 files changed, 13 insertions, 0 deletions

diff --git a/trace_reader.py b/trace_reader.py
index 2e5f65d..e18547e 100644
--- a/trace_reader.py
+++ b/trace_reader.py
@@ -53,12 +53,19 @@ def trace_reader(files):
 
     # We keep 100 records in each buffer and then keep the buffer sorted
     # This is because records may have been recorded slightly out of order
+    # This cannot guarantee records are produced in order, but it makes it
+    # overwhelmingly probably.
     for x in range(0,len(file_iter_buff)):
         for y in range(0,100):
             file_iter_buff[x].append(next(file_iters[x])) 
     for x in range(0,len(file_iter_buff)):
         file_iter_buff[x] = sorted(file_iter_buff[x],key=lambda rec: rec.when)
 
+    # Remember the time of the last record. This way, we can make sure records
+    # truly are produced in monotonically increasing order by time and terminate
+    # fatally if they are not.
+    last_time = None
+
     # Keep pulling records as long as we have a buffer
     while len(file_iter_buff) > 0:
 
@@ -87,6 +94,12 @@ def trace_reader(files):
                 del file_iter_buff[buff_to_refill]
                 del file_iters[buff_to_refill]
 
+        # Check for monotonically increasing time
+        if last_time is not None and earliest.when < last_time:
+            exit("FATAL ERROR: trace_reader.py: out-of-order record produced")
+        else:
+            last_time = earliest.when
+
         # Yield the record
         yield earliest