Message passing

[Bryan Ford]

>I suppose a
>debugger could live with the fact that process memory within the
>receive buffer is subject to change without notice if the process is
>waiting on a message.
>
>If we take this view, then speaking as a debugger author I want the
>kernel to provide an event of interest that is guaranteed to be after
>the message is completely transferred but before the process has
>executed any instructions following the receipt of the message.  [Term
>definition: "event of interest" goes back to the work on the UNIX
>debugger at AT&T. It refers to any event in the process's execution at
>which the debugger is able to get a notification that something
>happened.  In a well-designed debugging interface, the process can be
>halted on any event of interest.  An "event of interest" is alsy a
>synch point in the process model, in that the process state according
>to the process model must be well defined at any event of interest.]

That's already provided, because the trap/syscall instruction that
invokes the kernel message passing mechanism is considered "one instruction".
You can single-step across it or set a breakpoint immediately after it,
and the entire message send/receive operation will occur during the
execution of that single syscall instruction.

				Bryan