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< article >
< h1 > signal</ h1 >
< p > The < code > signal</ code > module provides Unix signal handling capabilities, allowing scripts to trap, ignore, or reset signal handlers.</ p >
< pre >< code > import "signal" for Signal</ code ></ pre >
< h2 > Signal Class</ h2 >
< div class = "class-header" >
< h3 > Signal</ h3 >
< p > Unix signal handling</ p >
</ div >
< h3 > Signal Constants</ h3 >
< table >
< tr >
< th > Constant</ th >
< th > Value</ th >
< th > Description</ th >
</ tr >
< tr >
< td >< code > Signal.SIGHUP</ code ></ td >
< td > 1</ td >
< td > Hangup (terminal closed or controlling process ended)</ td >
</ tr >
< tr >
< td >< code > Signal.SIGINT</ code ></ td >
< td > 2</ td >
< td > Interrupt (Ctrl+C)</ td >
</ tr >
< tr >
< td >< code > Signal.SIGQUIT</ code ></ td >
< td > 3</ td >
< td > Quit (Ctrl+\)</ td >
</ tr >
< tr >
< td >< code > Signal.SIGTERM</ code ></ td >
< td > 15</ td >
< td > Termination request</ td >
</ tr >
< tr >
< td >< code > Signal.SIGUSR1</ code ></ td >
< td > 10</ td >
< td > User-defined signal 1</ td >
</ tr >
< tr >
< td >< code > Signal.SIGUSR2</ code ></ td >
< td > 12</ td >
< td > User-defined signal 2</ td >
</ tr >
</ table >
< h3 > Static Methods</ h3 >
< div class = "method-signature" >
< span class = "method-name" > Signal.trap</ span > (< span class = "param" > signum</ span > , < span class = "param" > fn</ span > )
</ div >
< p > Registers a handler function to be called when the signal is received. The handler will be called each time the signal is received.</ p >
< ul class = "param-list" >
< li >< span class = "param-name" > signum</ span > < span class = "param-type" > (Num)</ span > - Signal number or constant</ li >
< li >< span class = "param-name" > fn</ span > < span class = "param-type" > (Fn)</ span > - Handler function (no arguments)</ li >
</ ul >
< pre >< code > Signal.trap(Signal.SIGINT) {
System.print("Caught Ctrl+C!")
}</ code ></ pre >
< div class = "method-signature" >
< span class = "method-name" > Signal.ignore</ span > (< span class = "param" > signum</ span > )
</ div >
< p > Ignores the specified signal. The signal will be delivered but have no effect.</ p >
< ul class = "param-list" >
< li >< span class = "param-name" > signum</ span > < span class = "param-type" > (Num)</ span > - Signal number to ignore</ li >
</ ul >
< pre >< code > Signal.ignore(Signal.SIGHUP)</ code ></ pre >
< div class = "method-signature" >
< span class = "method-name" > Signal.reset</ span > (< span class = "param" > signum</ span > )
</ div >
< p > Resets the signal handler to the default behavior.</ p >
< ul class = "param-list" >
< li >< span class = "param-name" > signum</ span > < span class = "param-type" > (Num)</ span > - Signal number to reset</ li >
</ ul >
< pre >< code > Signal.reset(Signal.SIGINT)</ code ></ pre >
< h2 > Examples</ h2 >
< h3 > Graceful Shutdown</ h3 >
< pre >< code > import "signal" for Signal
import "timer" for Timer
var running = true
Signal.trap(Signal.SIGINT) {
System.print("\nShutting down gracefully...")
running = false
}
Signal.trap(Signal.SIGTERM) {
System.print("\nReceived SIGTERM, shutting down...")
running = false
}
System.print("Server running. Press Ctrl+C to stop.")
while (running) {
Timer.sleep(1000)
}
System.print("Cleanup complete. Goodbye!")</ code ></ pre >
< h3 > Configuration Reload on SIGHUP</ h3 >
< pre >< code > import "signal" for Signal
import "timer" for Timer
import "io" for File
var config = {}
var loadConfig = Fn.new {
System.print("Loading configuration...")
if (File.exists("config.json")) {
var content = File.read("config.json")
System.print("Config loaded: %(content)")
}
}
loadConfig.call()
Signal.trap(Signal.SIGHUP) {
System.print("Received SIGHUP, reloading config...")
loadConfig.call()
}
System.print("Running. Send SIGHUP to reload config.")
while (true) {
Timer.sleep(1000)
}</ code ></ pre >
< h3 > Custom Signal for Debug Dump</ h3 >
< pre >< code > import "signal" for Signal
import "timer" for Timer
import "datetime" for DateTime
var requestCount = 0
var startTime = DateTime.now()
Signal.trap(Signal.SIGUSR1) {
System.print("=== Debug Dump ===")
System.print("Requests handled: %(requestCount)")
var uptime = DateTime.now() - startTime
System.print("Uptime: %(uptime.hours) hours")
System.print("==================")
}
System.print("Send SIGUSR1 for debug info (kill -USR1 pid)")
while (true) {
requestCount = requestCount + 1
Timer.sleep(100)
}</ code ></ pre >
< h3 > Ignoring Signals</ h3 >
< pre >< code > import "signal" for Signal
import "timer" for Timer
Signal.ignore(Signal.SIGINT)
System.print("SIGINT is now ignored. Ctrl+C will not stop this script.")
System.print("Use 'kill -9 pid' to force stop.")
for (i in 1..10) {
System.print("Still running... %(i)")
Timer.sleep(1000)
}
Signal.reset(Signal.SIGINT)
System.print("SIGINT handler restored. Ctrl+C works again.")</ code ></ pre >
< h3 > Multiple Signal Handlers</ h3 >
< pre >< code > import "signal" for Signal
import "timer" for Timer
var shutdownRequested = false
var forceShutdown = false
Signal.trap(Signal.SIGINT) {
if (shutdownRequested) {
System.print("\nForce shutdown!")
forceShutdown = true
} else {
System.print("\nGraceful shutdown requested. Press Ctrl+C again to force.")
shutdownRequested = true
}
}
Signal.trap(Signal.SIGTERM) {
System.print("\nSIGTERM received, shutting down immediately.")
forceShutdown = true
}
System.print("Running... Press Ctrl+C to stop.")
while (!forceShutdown) {
if (shutdownRequested) {
System.print("Cleaning up...")
Timer.sleep(500)
break
}
Timer.sleep(100)
}
System.print("Exited.")</ code ></ pre >
< h3 > Worker Process Control</ h3 >
< pre >< code > import "signal" for Signal
import "timer" for Timer
var paused = false
Signal.trap(Signal.SIGUSR1) {
paused = true
System.print("Worker paused")
}
Signal.trap(Signal.SIGUSR2) {
paused = false
System.print("Worker resumed")
}
System.print("Worker running. SIGUSR1 to pause, SIGUSR2 to resume.")
var count = 0
while (true) {
if (!paused) {
count = count + 1
System.print("Working... %(count)")
}
Timer.sleep(1000)
}</ code ></ pre >
< div class = "admonition note" >
< div class = "admonition-title" > Note</ div >
< p > Signal handling is only available on POSIX systems (Linux, macOS, BSD). On Windows, signal support is limited.</ p >
</ div >
< div class = "admonition warning" >
< div class = "admonition-title" > Warning</ div >
< p > Some signals like SIGKILL (9) and SIGSTOP (19) cannot be trapped or ignored. Attempting to do so will have no effect.</ p >
</ div >
< div class = "admonition tip" >
< div class = "admonition-title" > Tip</ div >
< p > Always implement graceful shutdown handlers for long-running services. Use SIGTERM for clean shutdowns and reserve SIGINT for interactive termination.</ p >
</ div >
</ article >
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