[e-lang] Questions: Close network connections, display command line from app, etrace

[Mark S. Miller]

Martin Scheffler wrote:
> -    How can I prevent or at least catch the killConnection error that
> I get on my server when I close a connected client?


A network partition or a vat termination breaks remote references. When a 
remote reference breaks, the object designated by this reference, such as your 
server, receives a __reactToLostClient(problem) message, notifying it that one 
of its clients allegedly might not be able to speak to it. (See sections 17.2 
and 11.5.3 of <http://erights.org/talks/thesis/>)

The provided problem argument is allegedly why one of its clients might not be 
able to communicate -- typically <SocketException: Connection reset>. Note 
that any client, local or remote, may send such a message of their own 
volition, even if no reference actually broke.


> -    How can I open a rune command line from a running script? I would
> like to be able to enter E commands into my program after it has
> started.


The rune function is defined in the privileged scope to act much like the rune 
shell command. For example, just like you can say

     $ rune --version

from the bash shell, you can say

     ? rune(["--version"])

from within a rune command line. Since the rune command with no arguments 
opens an interactive rune command line, from inside an E program you can call

     rune([])

or

     rune(["--interact", "-.e"])

to start an interactive rune command line. The source code of rune.e is:

-----------------------------------------------
#!/usr/bin/env rune

pragma.syntax("0.8")

# Copyright 2002 Combex, Inc. under the terms of the MIT X license
# found at http://www.opensource.org/licenses/mit-license.html ...............

def outcome :vow[boolean] := rune(interp.getArgs())

interp.waitAtTop(outcome)

interp.exitAtTop(Ref.optProblem(outcome))
-----------------------------------------------

The source for the rune function is 
src/esrc/org/erights/e/elang/cmd/runeAuthor.emaker, and will "explain" how 
rune is built up from various components.



> -   Can I tell E to output the etrace data directly to stderr instead
> of to a file?

You can set the "TraceLog_dir" property to "-", which indicates stderr rather
than an actual directory.

     $ rune -DTraceLog_dir=-

See <http://www.erights.org/elib/Tracing.html#controlling_the_log_at_launch_time>


-- 
Text by me above is hereby placed in the public domain

     Cheers,
     --MarkM