From: Michael Witrant <mike@...>
Date: 2001-12-13T03:39:41+09:00
Subject: [ruby-talk:28361] CGI::Session::FileStore and flock problem

Hello,

In cgi/session.rb, CGI::Session::FileStore uses IO#flock to lock the
session file while it's restoring it.

But:
1. it doesn't unlock the file when done. So the next #restore will wait
forever.
2. FileStore#update doesn't lock the file. So #update could change the
file while it's being restored.
3. flock isn't thread safe ([ruby-talk:16818]) and I think mod_ruby uses
threads to handle multiple requests. Could this be a problem?

See below for a patch that:
1. change #restore's flock to LOCK_SH instead of LOCK_EX
2. unlock when #restore is done
3. LOCK_EX and unlock on #update

What do you think?

Mike.


--- session.old	Mon Jun  4 10:59:56 2001
+++ session.rb	Wed Dec 12 19:29:59 2001
@@ -122,23 +122,32 @@
       def restore
 	unless @hash
 	  @hash = {}
-	  @f.flock File::LOCK_EX
-	  @f.rewind
-	  for line in @f
-	    line.chomp!
-	    k, v = line.split('=',2)
-	    @hash[CGI::unescape(k)] = CGI::unescape(v)
+	  @f.flock File::LOCK_SH
+	  begin
+	    @f.rewind
+	    for line in @f
+	      line.chomp!
+	      k, v = line.split('=',2)
+	      @hash[CGI::unescape(k)] = CGI::unescape(v)
+	    end
+	  ensure
+	    @f.flock File::LOCK_UN
 	  end
 	end
 	@hash
       end
 
       def update
-	@f.rewind
-	for k,v in @hash
-	  @f.printf "%s=%s\n", CGI::escape(k), CGI::escape(v)
+	@f.flock File::LOCK_EX
+	begin
+	  @f.rewind
+	  for k,v in @hash
+	    @f.printf "%s=%s\n", CGI::escape(k), CGI::escape(v)
+	  end
+	  @f.truncate @f.tell
+	ensure
+	  @f.flock File::LOCK_UN
 	end
-	@f.truncate @f.tell
       end
 
       def close