02-06-2003
If that's what you have to say then any form of Signal I/O is at stake.
External events which generates signals are not to our coding standard. They occur asynchronously at any time. Take an example in a signal driven I/O for Sockets:
When data arrives , the signal is generated. While the signal handler is executing ( reading data ) , two more data packets arrives at same time , causing signal to be generated two more times but as per our discussion the signal handler will be called only once. Hence the third data packet will only be read only when fourth data packet arrives at the port.
I feel that because signals are not queued ( to a process they are bit flags ) that the problem of multiple instances of same signal exists.
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LEARN ABOUT DEBIAN
signal
signal(3tcl) signal(3tcl)
NAME
signal - dynamically loadable signal handling for Tcl/Tk
SYNOPSIS
signal (add|delete|print|version) [options]
COMMANDS
add signo proc [-async]
Adds a signal handler for signal signo through proc proc. Signals can be provided by number, or the most common ones are provided by name
(e.g., SIGHUP). The proc is any Tcl procedure, and it is evaluated when the signal comes in. It will be provided no arguments.
Signal handlers have Posix semantics - they persist until reset.
If -async is used, the signal handler is created using Tcl_AsyncCreate(). Checks for the signal are very frequent (each evaluation) using
this technique, but one doesn't know quite where evaluation is or how to handle errors in this situation. The code will evaluate the pro-
vided procedure in the current interpreter if available, and in the interpreter which added the signal handler otherwise. At least until a
better scheme is suggested.
The -async is especially useful to interrupt "runaway" procs, or to cause a quick exit; the default mechanism simply waits for another
MainLoop cycle.
signal delete signo
Restores handling of signal signo to the default ( SIG_DFL ).
signal print
Prints the handling of all signals with handlers. Formatted as
signal ----> procedure or as
signal !---> procedure
if the signal is handled asynchronously
signal print signo
Prints the procedure for handling signal signo. Prints the word UNHANDLED if no signal handler is active for that signal.
signal version
Returns the string representing the current version of the package
AUTHOR
Michael Schwartz <mschwart@nyx.net>. Tilman Kranz <tilde@tk-sls.de> patched this for wider portability on Linux
Tcl Signal Extension 1.4.0.1 Tcl signal(3tcl)