bertrand@cui.unige.ch (IBRAHIM Bertrand) (05/02/89)
I am working on a computer aided learning project at the University
of Geneva using the X-windows Xray toolkit with an ADA interface on a SUN 3/60
workstation. I'm having a problem with multi-threaded access to the toolkit
and low-level X windows primitives.
My ADA program has several tasks which call into the Ada interface to Xrlib
which, in turn, calls the toolkit's C routines. Everything worked fine until I
put a call to XGet_Geometry() into one of the tasks. This caused the window
manager to hang and anonymous run-time error to appear: "sequence lost."
I could make everything fine again by embedding the XGet_Geometry() call
inside an ADA "rendezvous", thus suspending the other tasks for the duration
of the call. I could also make it work by surrounding all toolkit calls with
"Wait" and "Signal" calls to a semaphore task, thus confirming that the
toolkit won't support multi-threaded access.
The C code for each X Windows primitive locks and unlocks the display with
the macros "LockDisplay" and "UnlockDisplay" which, in my copy of the X Windows
source, are empty macros which do nothing. The manual says that these macros
can be defined for systems which want to support multi-threaded access.
My question is how can I make the Xray toolkit and the low-level
X Windows primitives support multi-threaded access? How are "LockDisplay" and
"UnlockDisplay" supposed to be implemented? (The C code can't possibly know
about ADA tasks.) Is there anyone else using the ADA interface who has
encountered this problem? I would appreciate any suggestions or comments.
I am using X11R2 on a Sun 3/60 running SUNOS3.5. The release of the Xray toolkit
is the one that arrived with the X11R2 tapes.
Thanks for any help.
Bertrand Ibrahim
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