Reopen stdout & stderr if redirected to error log

To use the logrotate utility, a USR1 signal is sent, and the
corresponding handler reopens the log files. However, sys.stdout and
sys.stderr, which may be redirected to the error log file, are not
updated. This commit fixes this, by closing the fileobj of the
LazyWriter object. There is no need to reopen it, since the LazyWriter
will open it when needed.

gunicorn/glogging.py

@@ -74,6 +74,16 @@ class LazyWriter(object):
                 self.lock.release()
         return self.fileobj
 
+    def close(self):
+        if self.fileobj:
+            self.lock.acquire()
+            try:
+                if self.fileobj:
+                    self.fileobj.close()
+                    self.fileobj = None
+            finally:
+                self.lock.release()
+
     def write(self, text):
         fileobj = self.open()
         fileobj.write(text)
@@ -239,6 +249,10 @@ class Logger(object):
 
 
     def reopen_files(self):
+        if self.cfg.errorlog != "-":
+            # Close stderr & stdout if they are redirected to error log file
+            sys.stderr.close()
+            sys.stdout.close()
         for log in loggers():
             for handler in log.handlers:
                 if isinstance(handler, logging.FileHandler):