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XCONTRAP
NM and CM callable (difference noted below).
Arms or disarms user-written subsystem break trap handling procedure.
Syntax
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| |
| I*V I* |
| XCONTRAP(plabel,oldplabel); |
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NOTE Any user trap handler cannot perform a GOTO out of that procedure.
Performing an ESCAPE (Pascal) or completing the trap handling
procedure are the only valid ways to return. The state of the
process and the program results are not predictable after a
non-local GOTO statement.
Parameters
plabel (NM) 32-bit signed integer by value (required)
(CM) 16-bit signed integer by value (required)
The plabel of the subsystem break trap handling
procedure. It can be either an NM or a CM plabel.
If the value is 0, the subsystem break trap handler
is disarmed for the process.
Obtaining external plabels for the NM trap handling
procedure depends on the programming language. In
Pascal/XL, for example, obtain the plabel by using
the waddress function. Supply the name of your
subsystem break trap handler as an argument to
waddress.
To pass a CM plabel, set it up as follows:
1. Obtain the 16-bit external CM plabel of the
CM subsystem break trap handler. One way to
do this is by using the LOADPROC intrinsic.
2. Pass this 16-bit plabel in the following
32-bit format:
(NM)
Bits Value/Meaning
31:1 Set to 1
30:1 Set to 0
29:1 Set to 1
16:13 Set to 0
0:16 16-bit external CM plabel
(CM)
Bits Value/Meaning
0:16 16-bit external CM plabel
oldplabel (NM) 32-bit signed integer passed by reference
(required)
(CM) 16-bit signed integer passed by reference
(required)
Returns the plabel of the process's previous
subsystem break trap handler. It can be either a
CM or NM plabel, as described above. If no plabel
was previously configured, oldplabel returns 0.
Operation Notes
Call XCONTRAP to arm a user-written subsystem break trap handling
procedure. This trap handler is invoked when an enabled subsystem break
signal is received during an interactive session. Calling XCONTRAP from
a job results in an error.
On most terminals, transmit the subsystem break signal by pressing CTRLY
(the default for sending a subsystem break signal). Subsystem break
traps are also referred to as control-Y traps.
Only one process in a session can receive a subsystem break trap at any
one time. The process that called XCONTRAP most recently receives the
next subsystem break trap. Once a process has received a subsystem break
trap, it cannot receive another until it calls the RESETCONTROL intrinsic
to reenable the subsystem break trap. Only processes running in a
session can enable subsystem break traps. The trap handler can be any
procedure in the program or in the libraries to which the program is
bound. The subsystem break trap handler has no parameters.
Condition Codes
CCE (2) Request granted. Trap enabled.
CCG (0) Request granted. Trap disabled.
CCL (1) Request denied. An illegal plabel or XCONTRAP was
called from a job.
Related Information
Intrinsics FCONTROL, FDEVICECONTROL, RESETCONTROL
Commands None
Manuals Trap Handling Programmer's Guide (32650-90026) and
Point-to-Point Workstation I/O Reference
(30000-90250)