Hello,
Attached is a patch of a fix I made to an issue we encountered with the
handling of the reader TLS (Thread Local Storage) keys in GIOPConn.
The issue was such that we had a call being made to a server, which
returned a reference to a generic resource. When the client receives
this, Mico does a _is_a query to verify it in the thread where the reply
was received. In our case this _is_a query went to another process with
a different connection which was just started by the server.
The problem was that the newly started connection created it's reader
threads, but then the query in the old connections reader thread calls
ORB:wait() to wait for the reply, and it determined that this is a
reader thread so it should directly call the dispatcher to wait for the
reply. Unfortunately, in this scenario it was the wrong reader thread,
and the new connections reader thread was also happily reading. This
ended up with a race in do_read(), where two threads would enter with
the do_read simultaneously causing a unpredictable condition.
Unfortunately I'm unable to produce a reasonable test case for it as
this occurred in a complex system, and was kind of rare and timing keen
(sometimes had to run the program in while loops until it occurred).
The exact issue is that the static
MICO::GIOPConn::is_this_reader_thread() method verifies whether current
thread is a reader, but doesn't care for which connection. I fixed this
by making it use the pointer to the GIOPConn instance as the thread
local keys value, so it can verify that it's a reader for the current
connection.
I'm not sure if this patch is perfectly correct (or more like I'm not
sure I fixed the right problem.) and whether it has any side effects. I
would be interested in comments and feedback on this patch.
Best regards,
--
Arne Pajunen
Software Engineer
OpenTTCN Oy, Test and Test Control Components for Test System Vendors
Web: http://www.openttcn.com
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