Signal
Inherits Enum / Comparable / Value / Object
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.seconds
Signal::INT.trap do
puts "Gotcha!"
end
puts "Ctrl+C will be caught from now on"
sleep 3.seconds
Signal::INT.reset
puts "Ctrl+C is back to the OS default action"
sleep 3.secondsWARNING: 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.
ABRT,FPE,ILL,INT,SEGV, andTERMare guaranteed to exist on all platforms.PWR,STKFLT, andUNUSEDonly exist on Linux.BREAKonly exists on Windows.- All other signals exist on all POSIX platforms.
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:
- The portable API for responding to a termination request is
Process.on_terminate. - The portable API for sending a
TERMorKILLsignal to a process isProcess#terminate. - The portable API for retrieving the exit signal of a process
(
Process::Status#exit_signal) isProcess::Status#exit_reason.
Constants
Instance methods
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.
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.
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 throughout 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.
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