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.
static VALUE
sig_list(VALUE _)
{
VALUE h = rb_hash_new();
const struct signals *sigs;
FOREACH_SIGNAL(sigs, 0) {
rb_hash_aset(h, rb_fstring_cstr(sigs->signm), INT2FIX(sigs->signo));
}
return h;
} 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}
static VALUE
sig_signame(VALUE recv, VALUE signo)
{
const char *signame = signo2signm(NUM2INT(signo));
if (!signame) return Qnil;
return rb_str_new_cstr(signame);
} Convert signal number to signal name. Returns nil if the signo is an invalid signal number.
Signal.trap("INT") { |signo| puts Signal.signame(signo) }
Process.kill("INT", 0)
produces:
INT
static VALUE
sig_trap(int argc, VALUE *argv, VALUE _)
{
int sig;
sighandler_t func;
VALUE cmd;
rb_check_arity(argc, 1, 2);
sig = trap_signm(argv[0]);
if (reserved_signal_p(sig)) {
const char *name = signo2signm(sig);
if (name)
rb_raise(rb_eArgError, "can't trap reserved signal: SIG%s", name);
else
rb_raise(rb_eArgError, "can't trap reserved signal: %d", sig);
}
if (argc == 1) {
cmd = rb_block_proc();
func = sighandler;
}
else {
cmd = argv[1];
func = trap_handler(&cmd, sig);
}
if (rb_obj_is_proc(cmd) &&
!rb_ractor_main_p() && !rb_ractor_shareable_p(cmd)) {
cmd = rb_proc_isolate(cmd);
}
return trap(sig, func, cmd);
} 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
Ruby Core © 1993–2020 Yukihiro Matsumoto
Licensed under the Ruby License.
Ruby Standard Library © contributors
Licensed under their own licenses.