Fix #19: Empty output with -m option

When one of the log files is empty and we use `-m` option we will get no
output, unlike normal operation that would output contents of all other
files correctly.

This patch fixes this by removing from the files to read empty ones like
we do once we start processing the files.

CHANGELOG.rst

@@ -6,6 +6,7 @@ Changelog
 
 **Features:**
 
+- Add optional reduced memory operation `-m` `--min-memory`
 - Add base log path option: `-b` `--log-base`.
 - Log postfix option: `-p` `--log-postfix`.
 - Auto alias generation: `-a` `--alias-level`.

oslogmerger/oslogmerger.py

@@ -180,24 +180,24 @@ class OpenStackLog:
 def process_logs_limit_memory_usage(logs):
     oslogs = [iter(log) for log in logs]
 
-    for log in oslogs:
-        next(log)
+    def process_entry(entry_iterable):
+        try:
+            next(entry_iterable)
+        except StopIteration:
+            # There are no more entries in the iterable, we can remove it
+            # from the list to process
+            oslogs.remove(entry_iterable)
 
-    while True:
-        entry = min(oslogs)
-        result = entry.peek()
+    for log in oslogs:
+        process_entry(log)
+
+    while oslogs:
+        entry_iterable = min(oslogs)
+        result = entry_iterable.peek()
         if result is None:
             break
         yield result
-        try:
-            next(entry)
-        except StopIteration:
-            # We don't need to remove the entry, since the code works with
-            # files that have reached the end, but there is no point in keep
-            # checking a file that has already reached the EOF.
-            oslogs.remove(entry)
-            if not oslogs:
-                break
+        process_entry(entry_iterable)
 
 
 def process_logs_memory_hog(logs):