On Tue, 13 Jun 2000, Dr Wes Munsil wrote:
> Please give me your advice.
>
> I've instrumented TclBlend to look for the pattern of execution of
> MonitorEnter/MonitorExit calls and have learned this. The deadlock seen
> in my code, and now in the TclBlend regression test
> AutomaticSignature.test on Solaris with native threads, has these
> characteristics:
>
> 1) Tclblend_Init is never called. Consequently the call of MonitorEnter
> in that function is never executed.
That does not seem right. The Tclblend_Init method should be
invoked by Tcl during the load command (like load libtclblend.so).
> 2) Although Jiang's patch removes the MonitorEnter and MonitorExit calls
> from JAVA_LOCK and JAVA_UNLOCK, there are still other calls of
> MonitorEnter and MonitorExit: they occur in Exit/Enter pairs in
> JavaIdleProc, JavaTraceProc, JavaCmdDeleteProc, JavaCmdProc,
> JavaEventProc, and JavaTimerProc.
I am guessing that there were older versions that never got
converted over to JAVA_LOCK and JAVA_UNLOCK.
> 3) The sequence of events leading up to deadlock is the following:
>
> a) the main thread calls MonitorExit in JavaCmdProc
> b) the garbage collection thread calls MonitorExit in JavaCmdDeleteProc
> c) the garbage collection thread calls MonitorEnter in JavaCmdDeleteProc
> d) the main thread calls MonitorEnter in JavaCmdProc (and blocks)
>
> I can think of two solutions to this problem, but I don't know which is
> "right."
>
> SOLUTION 1. Simply remove all remaining calls of MonitorEnter and
> MonitorExit.
> SOLUTION 2. Replace all remaining calls of MonitorEnter and MonitorExit
> by invocations of JAVA_LOCK and JAVA_UNLOCK, respectively (which now
> have the MonitorEnter and MonitorExit calls removed, but which retain
> the fiddling with the Java environment).
I think #2 is the better one. That way you can switch all locks
on and off. That is a really drastic approach, but it would
be interesting to see what happened.
> In either case, we should possibly discover why Tclblend_Init is not
> being called, and fix that.
This seems to be the main problem. Try compiling your C code
with -DTCLBLEND_DEBUG and see if anything about a call to
TclBlend_Init is printed. You can also set a BP in the Tcl
load command and then step into the load of libtclblend.so.
Mo DeJong
Red Hat Inc
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