Module: Signal

Defined in:
signal.c

Overview

Many operating systems allow signals to be sent to running processes. Some signals have a defined effect on the process, while others may be trapped at the code level and acted upon. For example, your process may trap the USR1 signal and use it to toggle debugging, and may use TERM to initiate a controlled shutdown.

pid = fork do
  Signal.trap("USR1") do
    $debug = !$debug
    puts "Debug now: #$debug"
  end
  Signal.trap("TERM") do
    puts "Terminating..."
    shutdown()
  end
  # . . . do some work . . .
end

Process.detach(pid)

# Controlling program:
Process.kill("USR1", pid)
# ...
Process.kill("USR1", pid)
# ...
Process.kill("TERM", pid)

produces:

 Debug now: true
 Debug now: false
Terminating...

The list of available signal names and their interpretation is system dependent. Signal delivery semantics may also vary between systems; in particular signal delivery may not always be reliable.

Class Method Summary (collapse)

Instance Method Summary (collapse)

Class Method Details

+ (Hash) list

Returns a list of signal names mapped to the corresponding underlying signal numbers.

Signal.list   #=> {"EXIT"=>0, "HUP"=>1, "INT"=>2, "QUIT"=>3, "ILL"=>4, "TRAP"=>5, "IOT"=>6, "ABRT"=>6, "FPE"=>8, "KILL"=>9, "BUS"=>7, "SEGV"=>11, "SYS"=>31, "PIPE"=>13, "ALRM"=>14, "TERM"=>15, "URG"=>23, "STOP"=>19, "TSTP"=>20, "CONT"=>18, "CHLD"=>17, "CLD"=>17, "TTIN"=>21, "TTOU"=>22, "IO"=>29, "XCPU"=>24, "XFSZ"=>25, "VTALRM"=>26, "PROF"=>27, "WINCH"=>28, "USR1"=>10, "USR2"=>12, "PWR"=>30, "POLL"=>29}

Returns:




# File 'signal.c'

static VALUE
sig_list(void)
{
VALUE h = rb_hash_new();
const struct signals *sigs;

for (sigs = siglist; sigs->signm; sigs++) {
rb_hash_aset(h, rb_str_new2(sigs->signm), INT2FIX(sigs->signo));
}

+ (Object) trap(signal, command) + (Object) trap(signal) {|| ... }

Specifies the handling of signals. The first parameter is a signal name (a string such as "SIGALRM", "SIGUSR1", and so on) or a signal number. The characters "SIG" may be omitted from the signal name. The command or block specifies code to be run when the signal is raised. If the command is the string "IGNORE" or "SIG_IGN", the signal will be ignored. If the command is "DEFAULT" or "SIG_DFL", the Ruby's default handler will be invoked. If the command is "EXIT", the script will be terminated by the signal. If the command is "SYSTEM_DEFAULT", the operating system's default handler will be invoked. Otherwise, the given command or block will be run. The special signal name "EXIT" or signal number zero will be invoked just prior to program termination. trap returns the previous handler for the given signal.

Signal.trap(0, proc { puts "Terminating: #{$$}" })
Signal.trap("CLD")  { puts "Child died" }
fork && Process.wait

produces:

Terminating: 27461
Child died
Terminating: 27460

Overloads:




# File 'signal.c'

static VALUE
sig_trap(int argc, VALUE *argv)
{
struct trap_arg arg;

rb_secure(2);
if (argc < 1 || argc > 2) {
rb_raise(rb_eArgError, "wrong number of arguments (%d for 1..2)", argc);
}

Instance Method Details

- (Object) new(sig_name) - (Object) new(sig_number[, name])

Construct a new SignalException object. sig_name should be a known

signal name.



# File 'signal.c'

static VALUE
esignal_init(int argc, VALUE *argv, VALUE self)
{
int argnum = 1;
VALUE sig = Qnil;
int signo;
const char *signm;

if (argc > 0) {
sig = rb_check_to_integer(argv[0], "to_int");
if (!NIL_P(sig)) argnum = 2;
else sig = argv[0];
}

- (Numeric) signo

Returns a signal number.

Returns:




# File 'signal.c'

static VALUE
esignal_signo(VALUE self)
{
    return rb_iv_get(self, "signo");
}