enum Signal

Overview

Safely handle inter-process signals on POSIX systems.

Signals are dispatched to the event loop and later processed in a dedicated fiber. Some received signals may never be processed when the program terminates.

puts "Ctrl+C still has the OS default action (stops the program)"
sleep 3

Signal::INT.trap do
  puts "Gotcha!"
end
puts "Ctrl+C will be caught from now on"
sleep 3

Signal::INT.reset
puts "Ctrl+C is back to the OS default action"
sleep 3

WARNING An uncaught exception in a signal handler is a fatal error.

Portability

The set of available signals is platform-dependent. Only signals that exist on the target platform are available as members of this enum.

The methods #trap, #reset, and #ignore may not be implemented at all on non-POSIX systems.

The standard library provides several platform-agnostic APIs to achieve tasks that are typically solved with signals on POSIX systems:

Defined in:

signal.cr

Enum Members

INT = 2
ILL = 4
FPE = 8
SEGV = 11
TERM = 15
ABRT = 6
HUP = 1
QUIT = 3
TRAP = 5
IOT = 6
KILL = 9
BUS = 7
SYS = 31
PIPE = 13
ALRM = 14
URG = 23
STOP = 19
TSTP = 20
CONT = 18
CHLD = 17
TTIN = 21
TTOU = 22
IO = 29
XCPU = 24
XFSZ = 25
VTALRM = 26
USR1 = 10
USR2 = 12
WINCH = 28
PWR = 30
STKFLT = 16
UNUSED = 31

Instance Method Summary

Instance methods inherited from struct Enum

&(other : self) : self &, +(other : Int) : self +, -(other : Int) : self -, <=>(other : self) <=>, ==(other : self)
==(other)
==
, ^(other : self) : self ^, |(other : self) : self |, ~ : self ~, clone clone, each(& : self -> ) each, hash(hasher) hash, includes?(other : self) : Bool includes?, inspect(io : IO) : Nil inspect, to_f32 : Float32 to_f32, to_f32! : Float32 to_f32!, to_f64 : Float64 to_f64, to_f64! : Float64 to_f64!, to_i : Int32 to_i, to_i128 : Int128 to_i128, to_i128! : Int128 to_i128!, to_i16 : Int16 to_i16, to_i16! : Int16 to_i16!, to_i32 : Int32 to_i32, to_i32! : Int32 to_i32!, to_i64 : Int64 to_i64, to_i64! : Int64 to_i64!, to_i8 : Int8 to_i8, to_i8! : Int8 to_i8!, to_json(json : JSON::Builder) to_json, to_s(io : IO) : Nil
to_s : String
to_s
, to_u128 : UInt128 to_u128, to_u128! : UInt128 to_u128!, to_u16 : UInt16 to_u16, to_u16! : UInt16 to_u16!, to_u32 : UInt32 to_u32, to_u32! : UInt32 to_u32!, to_u64 : UInt64 to_u64, to_u64! : UInt64 to_u64!, to_u8 : UInt8 to_u8, to_u8! : UInt8 to_u8!, to_yaml(yaml : YAML::Nodes::Builder) to_yaml, value : Int value

Constructor methods inherited from struct Enum

from_value(value : Int) : self from_value, new(ctx : YAML::ParseContext, node : YAML::Nodes::Node)
new(value : self)
new(pull : JSON::PullParser)
new
, parse(string : String) : self parse

Class methods inherited from struct Enum

each(& : self -> ) each, from_value?(value : Int) : self | Nil from_value?, names : Array(String) names, parse?(string : String) : self | Nil parse?, valid?(value : self) : Bool valid?, values : Array(self) values

Macros inherited from struct Enum

[](*values) [], flags(*values) flags

Instance methods inherited from module Comparable(Enum)

<(other : T) : Bool <, <=(other : T) <=, <=>(other : T) <=>, ==(other : T) ==, >(other : T) : Bool >, >=(other : T) >=, clamp(min, max)
clamp(range : Range)
clamp

Instance methods inherited from struct Value

==(other : JSON::Any)
==(other : YAML::Any)
==(other)
==
, dup dup

Instance methods inherited from class Object

! : Bool !, !=(other) !=, !~(other) !~, ==(other) ==, ===(other : JSON::Any)
===(other : YAML::Any)
===(other)
===
, =~(other) =~, as(type : Class) as, as?(type : Class) as?, class class, dup dup, hash(hasher)
hash
hash
, in?(collection : Object) : Bool
in?(*values : Object) : Bool
in?
, inspect(io : IO) : Nil
inspect : String
inspect
, is_a?(type : Class) : Bool is_a?, itself itself, nil? : Bool nil?, not_nil!(message)
not_nil!
not_nil!
, pretty_inspect(width = 79, newline = "\n", indent = 0) : String pretty_inspect, pretty_print(pp : PrettyPrint) : Nil pretty_print, responds_to?(name : Symbol) : Bool responds_to?, tap(&) tap, to_json(io : IO) : Nil
to_json : String
to_json
, to_pretty_json(indent : String = " ") : String
to_pretty_json(io : IO, indent : String = " ") : Nil
to_pretty_json
, to_s(io : IO) : Nil
to_s : String
to_s
, to_yaml(io : IO) : Nil
to_yaml : String
to_yaml
, try(&) try, unsafe_as(type : T.class) forall T unsafe_as

Class methods inherited from class Object

from_json(string_or_io, root : String)
from_json(string_or_io)
from_json
, from_yaml(string_or_io : String | IO) from_yaml

Macros inherited from class Object

class_getter(*names, &block) class_getter, class_getter!(*names) class_getter!, class_getter?(*names, &block) class_getter?, class_property(*names, &block) class_property, class_property!(*names) class_property!, class_property?(*names, &block) class_property?, class_setter(*names) class_setter, def_clone def_clone, def_equals(*fields) def_equals, def_equals_and_hash(*fields) def_equals_and_hash, def_hash(*fields) def_hash, delegate(*methods, to object) delegate, forward_missing_to(delegate) forward_missing_to, getter(*names, &block) getter, getter!(*names) getter!, getter?(*names, &block) getter?, property(*names, &block) property, property!(*names) property!, property?(*names, &block) property?, setter(*names) setter

Instance Method Detail

def abrt? #

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def alrm? #

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def bus? #

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def chld? #

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def cont? #

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def fpe? #

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def hup? #

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def ignore : Nil #

Clears the handler for this signal and prevents the OS default action.

Note that trying to ignore CHLD will actually set the default crystal handler that monitors and reaps child processes. This prevents zombie processes and is required by Process#wait for example.


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def ill? #

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def int? #

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def io? #

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def iot? #

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def kill? #

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def pipe? #

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def pwr? #

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def quit? #

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def reset : Nil #

Resets the handler for this signal to the OS default.

Note that trying to reset CHLD will actually set the default crystal handler that monitors and reaps child processes. This prevents zombie processes and is required by Process#wait for example.


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def segv? #

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def stkflt? #

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def stop? #

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def sys? #

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def term? #

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def trap(&handler : Signal -> ) : Nil #

Sets the handler for this signal to the passed function.

After executing this, whenever the current process receives the corresponding signal, the passed function will be called (instead of the OS default). The handler will run in a signal-safe fiber thought the event loop; there is no limit to what functions can be called, unlike raw signals that run on the sigaltstack.

Note that CHLD is always trapped and child processes will always be reaped before the custom handler is called, hence a custom CHLD handler must check child processes using Process.exists?. Trying to use waitpid with a zero or negative value won't work.

NOTE Process.on_terminate is preferred over Signal::INT.trap as a portable alternative which also works on Windows.


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def trap? #

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def trap_handler? #

Returns any existing handler for this signal

Signal::USR1.trap { }
prev_handler = Signal::USR1.trap_handler?

Signal::USR1.trap do |signal|
  prev_handler.try &.call(signal)
  # ...
end

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def tstp? #

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def ttin? #

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def ttou? #

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def unused? #

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def urg? #

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def usr1? #

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def usr2? #

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def vtalrm? #

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def winch? #

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def xcpu? #

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def xfsz? #

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