Handle a signal
Most general purpose operating systems provide interrupt facilities, sometimes called signals. Unhandled signals generally terminate a program in a disorderly manner. Signal handlers are created so that the program behaves in a well-defined manner upon receipt of a signal.
You are encouraged to solve this task according to the task description, using any language you may know.
For this task you will provide a program that displays a single integer on each line of output at the rate of one integer in each half second. Upon receipt of the SigInt signal (often created by the user typing ctrl-C) the program will cease printing integers to its output, print the number of seconds the program has run, and then the program will terminate.
Ada
Signal Handler
Ada signal handlers must be defined at the library level. The following package defines a simple signal handler for the SigInt signal. <lang ada>with Ada.Interrupts; use Ada.Interrupts; with Ada.Interrupts.Names; use Ada.Interrupts.Names;
package Sigint_Handler is
protected Handler is
entry Wait;
procedure Handle;
pragma Interrupt_Handler(Handle);
pragma Attach_Handler(Handle, Sigint);
private
Call_Count : Natural := 0;
end Handler;
end Sigint_Handler;</lang> <lang ada>package body Sigint_Handler is
------------- -- Handler -- -------------
protected body Handler is
----------
-- Wait --
----------
entry Wait when Call_Count > 0 is
begin
Call_Count := Call_Count - 1;
end Wait;
------------
-- Handle --
------------
procedure Handle is
begin
Call_Count := Call_Count + 1;
end Handle;
end Handler;
end Sigint_Handler;</lang> A signal may be received at any time in a program. Ada signal handling requires a task to suspend on an entry call for the handler which is executed only when the signal has been received. The following program uses the interrupt handler defined above to deal with receipt of SigInt. <lang ada>with Ada.Calendar; use Ada.Calendar; with Ada.Text_Io; use Ada.Text_Io; with Sigint_Handler; use Sigint_Handler;
procedure Signals is
task Counter is
entry Stop;
end Counter;
task body Counter is
Current_Count : Natural := 0;
begin
loop
select
accept Stop;
exit;
or delay 0.5;
end select;
Current_Count := Current_Count + 1;
Put_Line(Natural'Image(Current_Count));
end loop;
end Counter;
task Sig_Handler;
task body Sig_Handler is
Start_Time : Time := Clock;
Sig_Time : Time;
begin
Handler.Wait;
Sig_Time := Clock;
Counter.Stop;
Put_Line("Program execution took" & Duration'Image(Sig_Time - Start_Time) & " seconds");
end Sig_Handler;
begin
null;
end Signals;</lang> Sample Output
1 2 3 4 5 6 7 8 Program execution took 4.348057086 seconds
BBC BASIC
This program runs only in console mode; it must be compiled and then run as an EXE. <lang bbcbasic> REM!Exefile C:\bbcsigint.exe,encrypt,console
INSTALL @lib$+"CALLBACK"
CTRL_C_EVENT = 0
SYS "GetStdHandle", -10 TO @hfile%(1)
SYS "GetStdHandle", -11 TO @hfile%(2)
*INPUT 13
*OUTPUT 14
ON ERROR PRINT REPORT$ : QUIT ERR
CtrlC% = FALSE
handler% = FN_callback(FNsigint(), 1)
SYS FN_syscalls("SetConsoleCtrlHandler"), handler%, 1 TO !FN_systo(res%)
IF res%=0 PRINT "Could not set SIGINT handler" : QUIT 1
PRINT "Press Ctrl+C to test...."
TIME = 0
Time% = 50
REPEAT
WAIT 1
IF TIME > Time% THEN
PRINT Time%
Time% += 50
ENDIF
UNTIL CtrlC%
PRINT "Ctrl+C was pressed after "; TIME/100 " seconds."
QUIT
DEF FNsigint(T%)
CASE T% OF
WHEN CTRL_C_EVENT: CtrlC% = TRUE : = 1
ENDCASE
= 0</lang>
Output:
C:\>bbcsigint
Press Ctrl+C to test....
50
100
150
200
250
Ctrl+C was pressed after 2.72 seconds.
C:\>
C
Standard C's sleep() only provides one-second resolution, so the POSIX usleep() function is used here. (POSIX is not needed for the actual signal handling part.) <lang C>#include <stdio.h>
- include <stdlib.h> // for exit()
- include <signal.h>
- include <time.h> // for clock()
- include <unistd.h> // for POSIX usleep()
volatile sig_atomic_t gotint = 0;
void handleSigint() {
/*
* Signal safety: It is not safe to call clock(), printf(),
* or exit() inside a signal handler. Instead, we set a flag.
*/
gotint = 1;
}
int main() {
clock_t startTime = clock();
signal(SIGINT, handleSigint);
int i=0;
for (;;) {
if (gotint)
break;
usleep(500000);
if (gotint)
break;
printf("%d\n", ++i);
}
clock_t endTime = clock();
double td = (endTime - startTime) / (double)CLOCKS_PER_SEC;
printf("Program has run for %5.3f seconds\n", td);
return 0;
}</lang>
Sample Output
1 2 3 Program has run for 1.953 seconds
C#
Signals in C# are called events, and are handled by attaching event handler functions to the event, which are called when the event is triggered.
<lang csharp>using System; //DateTime, Console, Environment classes class Program {
static DateTime start;
static void Main(string[] args)
{
start = DateTime.Now;
//Add event handler for Ctrl+C command
Console.CancelKeyPress += new ConsoleCancelEventHandler(Console_CancelKeyPress);
int counter = 0;
while (true)
{
Console.WriteLine(++counter);
System.Threading.Thread.Sleep(500);
}
}
static void Console_CancelKeyPress(object sender, ConsoleCancelEventArgs e)
{
var end = DateTime.Now;
Console.WriteLine("This program ran for {0:000.000} seconds.", (end - start).TotalMilliseconds / 1000);
Environment.Exit(0);
}
}</lang>
Forth
Normally Gforth handles most signals (e.g., the user interrupt SIGINT, or the segmentation violation SIGSEGV) by translating it into a Forth THROW.
<lang forth>-28 constant SIGINT
- numbers ( n -- n' )
begin dup . cr 1+ 500 ms again ;
- main
utime 0 begin ['] numbers catch SIGINT = until drop utime d- dnegate <# # # # # # # [char] . hold #s #> type ." seconds" ;
main bye</lang>
F#
<lang fsharp>open System
let rec loop n = Console.WriteLine( n:int )
Threading.Thread.Sleep( 500 )
loop (n + 1)
let main() =
let start = DateTime.Now
Console.CancelKeyPress.Add(
fun _ -> let span = DateTime.Now - start
printfn "Program has run for %.0f seconds" span.TotalSeconds
)
loop 1
main()</lang>
Go
<lang go>package main
import (
"fmt" "os" "os/signal" "time"
)
func main() {
start := time.Now()
k := time.NewTicker(time.Second / 2)
sc := make(chan os.Signal, 1)
signal.Notify(sc, os.Interrupt)
for n := 1; ; {
// not busy waiting, this blocks until one of the two
// channel operations is possible
select {
case <-k.C:
fmt.Println(n)
n++
case <-sc:
fmt.Printf("Ran for %f seconds.\n",
time.Now().Sub(start).Seconds())
return
}
}
}</lang>
- Output:
1 2 3 ^C Ran for 1.804877 seconds.
Haskell
<lang haskell>import Prelude hiding (catch) import Control.Exception (catch, throwIO, AsyncException(UserInterrupt)) import Data.Time.Clock (getCurrentTime, diffUTCTime) import Control.Concurrent (threadDelay)
main = do t0 <- getCurrentTime
catch (loop 0)
(\e -> if e == UserInterrupt
then do t1 <- getCurrentTime
putStrLn ("\nTime: " ++ show (diffUTCTime t1 t0))
else throwIO e)
loop i = do print i
threadDelay 500000 {- µs -}
loop (i + 1)</lang>
HicEst
Subroutines "F2" to "F9" can be called any time by the F2...F9 keys or by a mouse click on the toolbar buttons "F2" to "F9". These buttons appear as soon as a SUBROUTINE "F2" to "F9" statement is compiled: <lang HicEst>seconds = TIME()
DO i = 1, 1E100 ! "forever"
SYSTEM(WAIT = 500) ! milli seconds WRITE(Name) i
ENDDO
SUBROUTINE F2 ! call by either the F2 key, or by a toolbar-F2 click
seconds = TIME() - seconds WRITE(Messagebox, Name) seconds ALARM(999) ! quit immediately
END</lang>
Java
Use of sun.misc.SignalHandler allows one to specify which signal to catch, though is unsupported and potentially not available in all JVMs
<lang java>import sun.misc.Signal; import sun.misc.SignalHandler;
public class ExampleSignalHandler {
public static void main(String... args) throws InterruptedException {
final long start = System.nanoTime();
Signal.handle(new Signal("INT"), new SignalHandler() {
public void handle(Signal sig) {
System.out.format("\nProgram execution took %f seconds\n", (System.nanoTime() - start) / 1e9f);
System.exit(0);
}
});
int counter = 0;
while(true) {
System.out.println(counter++);
Thread.sleep(500);
}
}
} </lang>
Or one can use a generic shutdown hook as follows, though a reference to the particular signal is not available.
<lang java>public class ExampleSignalHandler {
public static void main(String... args) throws InterruptedException {
final long start = System.nanoTime();
Runtime.getRuntime().addShutdownHook(new Thread(new Runnable() {
public void run() {
System.out.format("\nProgram execution took %f seconds\n", (System.nanoTime() - start) / 1e9f);
}
}));
int counter = 0;
while(true) {
System.out.println(counter++);
Thread.sleep(500);
}
}
} </lang>
Liberty BASIC
Liberty BASIC cannot react to a SigInt signal and truly kill itself. The best it can do is respond to Ctrl-C by exiting normally. <lang lb> nomainwin WindowHeight=DisplayHeight open "Handle a signal" for graphics as #1
- 1 "trapclose [quit]"
- 1 "down;setfocus;place 10 20"
- 1 "\Press CTRL + C to stop."
- 1 "when characterInput [keyPressed]"
start=time$("ms") timer 500, [doPrint] wait [quit] close #1:end
[doPrint]
if sigInt then
timer 0
#1 "\Seconds elapsed: ";(time$("ms")-start)/1000
else
i=i+1
if i mod 20 = 0 then #1 "cls;place 10 20"
#1 "\";i
end if
wait
[keyPressed]
if len(Inkey$)>1 then if left$(Inkey$,1)=chr$(8) then sigCtrl=1 else sigCtrl=0 end if if sigCtrl=1 and Inkey$=chr$(3) then sigInt=1 wait </lang>
OCaml
OCaml's Unix.sleep doesn't handle non-integral arguments, so this program prints a number every second.
<lang ocaml>#load "unix.cma";; (* for sleep and gettimeofday; not needed for the signals stuff per se *)
let start = Unix.gettimeofday ();;
Sys.set_signal Sys.sigint
(Sys.Signal_handle (fun _signum ->
Printf.printf "Ran for %f seconds.\n"
(Unix.gettimeofday () -. start);
exit 0));;
let rec loop n =
Printf.printf "%d\n%!" n; Unix.sleep 1; loop (n + 1)
in
loop 1;;</lang>
Perl
Perl's (in fact Unix's) sleep doesn't handle non-integral arguments correctly on some platforms, so this program uses the select syscall for timeout.
<lang perl>my $start = time;
$SIG{INT} = sub
{print 'Ran for ', time - $start, " seconds.\n";
exit;};
for (my $n = 0 ;; select(undef, undef, undef, .5))
{print ++$n, "\n";}</lang>
This example does the required task: <lang perl>use 5.010; use AnyEvent; my $start = AE::time; my $exit = AE::cv; my $int = AE::signal 'INT', $exit; my $n; my $num = AE::timer 0, 0.5, sub { say $n++ }; $exit->recv; say " interrupted after ", AE::time - $start, " seconds";</lang>
Sample output:
0 1 2 3 4 5 6 7 8 9 10 ^C interrupted after 5.23734092712402 seconds
PHP
<lang php><?php declare(ticks = 1);
$start = microtime(YES);
function mySigHandler() {
global $start; $elapsed = microtime(YES) - $start; echo "Ran for $elapsed seconds.\n"; exit();
}
pcntl_signal(SIGINT, 'mySigHandler');
for ($n = 0; ; usleep(500000)) // 0.5 seconds
echo ++$n, "\n";
?></lang>
PicoLisp
Put the following into a file, set it to executable, and run it <lang PicoLisp>#!/usr/bin/picolisp /usr/lib/picolisp/lib.l
(push '*Bye '(println (*/ (usec) 1000000)) '(prinl))
(let Cnt 0
(loop
(println (inc 'Cnt))
(wait 500) ) )</lang>
PL/I
<lang> handler: procedure options (main);
declare i fixed binary (31);
declare (start_time, finish_time) float (18);
on attention begin;
finish_time = secs();
put skip list ('elapsed time =', finish_time - start_time, 'secs');
stop;
end;
start_time = secs();
do i = 1 by 1;
delay (500);
put skip list (i);
end;
end handler; </lang>
PureBasic
This code is for Windows only due to the usage of SetConsoleCtrlHandler() <lang PureBasic>CompilerIf #PB_Compiler_OS<>#PB_OS_Windows
CompilerError "This code is Windows only"
CompilerEndIf
Global Quit, i, T0=ElapsedMilliseconds(), T1
Procedure CtrlC()
T1=ElapsedMilliseconds() Quit=1 While i: Delay(1): Wend
EndProcedure
If OpenConsole()
SetConsoleCtrlHandler_(@CtrlC(),#True)
While Not Quit
PrintN(Str(i))
i+1
Delay(500)
Wend
PrintN("Program has run for "+StrF((T1-T0)/1000,3)+" seconds.")
Print ("Press ENTER to exit."):Input(): i=0
EndIf</lang>
0 1 2 3 4 Program has run for 2.121 seconds. Press ENTER to exit.
Python
The following example should work on all platforms. <lang python>import time
def intrptWIN():
procDone = False n = 0
while not procDone:
try:
time.sleep(0.5)
n += 1
print n
except KeyboardInterrupt, e:
procDone = True
t1 = time.time() intrptWIN() tdelt = time.time() - t1 print 'Program has run for %5.3f seconds.' % tdelt</lang>
There is a signal module in the standard distribution that accomodates the UNIX type signal mechanism. However the pause() mechanism is not implemented on Windows versions. <lang python>import signal, time, threading done = False n = 0
def counter():
global n, timer n += 1 print n timer = threading.Timer(0.5, counter) timer.start()
def sigIntHandler(signum, frame):
global done timer.cancel() done = True
def intrptUNIX():
global timer signal.signal(signal.SIGINT, sigIntHandler)
timer = threading.Timer(0.5, counter)
timer.start()
while not done:
signal.pause()
t1 = time.time() intrptUNIX() tdelt = time.time() - t1 print 'Program has run for %5.3f seconds.' % tdelt</lang>
How about this one? It should work on all platforms; and it does show how to install a signal handler: <lang python>import time, signal
class WeAreDoneException(Exception):
pass
def sigIntHandler(signum, frame):
signal.signal(signal.SIGINT, signal.SIG_DFL) # resets to default handler raise WeAreDoneException
t1 = time.time()
try:
signal.signal(signal.SIGINT, sigIntHandler)
n = 0
while True:
time.sleep(0.5)
n += 1
print n
except WeAreDoneException:
pass
tdelt = time.time() - t1 print 'Program has run for %5.3f seconds.' % tdelt</lang>
REXX
REXX has no SLEEP function that is built into the language.
Some operating systems that REXX runs under have a SLEEP or equivalent function.
But, there's more than one way to skin a cat. (No offense to cat lovers.)
<lang>/*REXX program displays integers until a Ctrl─C is pressed, then show*/
/* the number of seconds that have elapsed since start of pgm execution.*/
call time 'E' /*reset the REXX elapsed timer. */ signal on halt /*HALT is signaled via a Ctrl─C.*/
do j=1 /*start with 1 and go ye forth. */
say right(j,20) /*display integer right-justified*/
t=time('E') /*get the elapsed time in seconds*/
do forever; u=time('E') /*get the elapsed time in seconds./
if u◄t |, /* ◄═══ means we passed midnight.*/
u>t+.5 then iterate j /* ◄═══ means we passed ½ second.*/
end /*forever*/
end /*j*/
say 'Program control should never ever get here, said Captain Dunsel.'
/*──────────────────────────────────HALT subroutine─────────────────────*/ halt: say 'program HALTed, it ran for' format(time("E"),,2) 'seconds.'
/*stick a fork in it, we're done.*/</lang>
output
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
^C
program HALTed, it ran for 11.53 seconds.
Note: some REXX interpreters don't show the
^C
Ruby
<lang ruby>t1 = Time.now
catch :done do
Signal.trap('INT') do
Signal.trap('INT', 'DEFAULT') # reset to default
throw :done
end
n = 0
loop do
sleep(0.5)
n += 1
puts n
end
end
tdelt = Time.now - t1 puts 'Program has run for %5.3f seconds.' % tdelt</lang>
Smalltalk
<lang smalltalk> |n|
n := 0.
UserInterrupt
catch:[
[true] whileTrue:[
n := n + 1.
n printCR.
Delay waitForSeconds: 0.5.
]
]</lang>
attaching an OS-signal (unix signal) to an exception or signal instance: <lang smalltalk>|mySignal| mySignal := Signal new mayProceed: false. OperatingSytem operatingSystemSignal: (OperatingSytsem signalNamed:'SIGHUP') install: mySignal. [
.. do something...
] on: mySignal do:[
... handle SIGHUP gracefully...
]</lang> this is normally not needed, as the runtime system already catches common unix signals and arranges for an OSError to be raised; so user code normally does not need to care for this.
Tcl
Core Tcl does not have signal handling. However the Expect and TclX extension packages do.
Using Expect: <lang tcl>package require Expect
proc sigint_handler {} {
puts "elapsed time: [expr {[clock seconds] - $::start_time}] seconds"
set ::looping false
}
trap sigint_handler SIGINT
set start_time [clock seconds] set n 0 set looping true while {$looping} {
puts [incr n] after 500
}</lang>
Similarly, with TclX: <lang tcl>package require Tclx
proc sigint_handler {} {
puts "elapsed time: [expr {[clock seconds] - $::start_time}] seconds"
set ::looping false
}
signal trap sigint sigint_handler
set start_time [clock seconds] set n 0 set looping true while {$looping} {
puts [incr n] after 500
}</lang>
With TclX, you don't have to trap signals, you can convert the signal into a catchable error: <lang tcl>package require Tclx
signal error sigint
set start_time [clock seconds] set n 0 proc infinite_loop {} {
while 1 {
puts [incr n]
after 500
}
} if {[catch infinite_loop out] != 0} {
lassign $::errorCode class name msg
if {$class eq "POSIX" && $name eq "SIG" && $msg eq "SIGINT"} {
puts "elapsed time: [expr {[clock seconds] - $start_time}] seconds"
} else {
puts "infinite loop interrupted, but not on SIGINT: $::errorInfo"
}
}</lang> With Tcl 8.6, that would be written as: <lang tcl>package require Tclx
signal error sigint
set start_time [clock seconds] proc infinite_loop {} {
while 1 {
puts [incr n]
after 500
}
} try {
infinite_loop
} trap {POSIX SIG SIGINT} {} {
puts "elapsed time: [expr {[clock seconds] - $start_time}] seconds"
}</lang> Note also that from 8.5 onwards, Tcl also has other mechanisms for delivering interrupt-like things, such as interpreter resource limits which permit stopping an execution after a set amount of time and returning control to a supervisor module. However, this is not driven by user interrupts and is so only tangential to this task.
X86 Assembly
Now, I realize linking to C libraries is somewhat cheating. It is entirely possible to do this entirely in syscalls using sys_nanosleep/sys_write but that would require allot more work, definition of the timespec structure among other things. <lang asm> %define sys_signal 48 %define SIGINT 2 %define sys_time 13
extern usleep extern printf
section .text global _start
_sig_handler: mov ebx, end_time mov eax, sys_time int 0x80 mov eax, dword [start_time] mov ebx, dword [end_time] sub ebx, eax mov ax, 100 div ebx push ebx push p_time call printf push 0x1 mov eax, 1 push eax int 0x80 ret
_start: mov ebx, start_time mov eax, sys_time int 0x80 mov ecx, _sig_handler mov ebx, SIGINT mov eax, sys_signal int 0x80 xor edi, edi .looper: push 500000 call usleep push edi push p_cnt call printf inc edi jmp .looper
section .data p_time db "The program has run for %d seconds.",13,10,0 p_cnt db "%d",13,10,0
section .bss start_time resd 1 end_time resd 1 </lang>
UNIX Shell
The timing will drift with this example (because we need to consider processing time on top of the wait), but the task demonstrates signal handling. For a more accurate timer, we need to implement a signalling process that signals the shell every half a second.
<lang bash>c="1"
- Trap signals for SIGQUIT (3), SIGABRT (6) and SIGTERM (15)
trap "echo -n 'We ran for ';echo -n `expr $c /2`; echo " seconds"; exit" 3 6 15 while [ "$c" -ne 0 ]; do # infinite loop
# wait 0.5 # We need a helper program for the half second interval c=`expr $c + 1`
done</lang>
<lang bash>TRAPINT(){ print $n; exit } for (( n = 0; ; n++)) sleep 1</lang>