[ros-dev] I/O subsystem question

Ge van Geldorp gvg at reactos.com
Mon Sep 12 09:43:41 CEST 2005

I'm working on bug 713 (http://www.reactos.com/bugzilla/show_bug.cgi?id=713
for the click-happy). What I have found is this:
- Telnet opens a socket
- Sending and receiving are handled by different threads, let's call them S
and R
- Thread R starts a recv() operation, which is translated to an ioctl on the
- No data is available, so thread R blocks, waiting for FileObject->Event
- I type something, which is handled by thread S. Thread S starts a send()
- Again translated to an ioctl on the socket. Since this is the same socket
as used by S, the FileObject will be the same
- The send can complete immediately, IoCompleteRequest is called which sets
the FileObject->Event.
- Thread R is unblocked, the event it was waiting for was set by thread S.
However, the irp of thread R was never completed. The recv() call returns
with bogus info.
- Thread R starts another recv(). When some data arrives from the server,
two irps are waiting for it. This eventually leads to the crash.

The fundamental problem seems to be multiple overlapping I/O operations
which all use FileObject->Event to signal their completion. I have no idea
how to fix that...

Gé van Geldorp.

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