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Send Signal IPC (signal)

Sends a signal RPC

Description

signal sends an operating system RPC (known as “signal”) to a specified process, identified via it’s process ID (“pid”).

The following quote from Wikipedia explains what signals are:

Signals are standardized messages sent to a running program to trigger specific behavior, such as quitting or error handling. They are a limited form of inter-process communication (IPC), typically used in Unix, Unix-like, and other POSIX-compliant operating systems.

A signal is an asynchronous notification sent to a process or to a specific thread within the same process to notify it of an event. Common uses of signals are to interrupt, suspend, terminate or kill a process.

Listing supported signals

Signals will differ from one operating system to another. You can retrieve a JSON map with supported signals by running signal without any parameters.

Usage

Send a signal:

1. The first parameter is the process ID (int)
2. The second parameter is the signal name (str). This will be all in UPPERCASE and prefixed “SIG”

signal pid SIGNAL

List supported signals:

signal -> <stdout>

Examples

Send a signal

function signal.SIGUSR1.trap {
    bg {
        exec <pid:MOD.SIGNAL_TRAP_PID> $MUREX_EXE -c %(
            event onSignalReceived example=SIGUSR1 {
                out "SIGUSR1 received..."
            }

            out "waiting for signal..."
            sleep 5
        )
    }
    sleep 2 # just in case `exec` hasn't started yet
    signal $MOD.SIGNAL_TRAP_PID SIGUSR1
}

test unit function signal.SIGUSR1.trap %{
    StdoutMatch: "waiting for signal...\nSIGUSR1 received...\n"
    DataType:    str
    ExitNum:     0
}

List supported signals

» signal
{
    "SIGABRT": "aborted",
    "SIGALRM": "alarm clock",
    "SIGBUS": "bus error",
    "SIGCHLD": "child exited",
    "SIGCONT": "continued",
    "SIGFPE": "floating point exception",
    "SIGHUP": "hangup",
    "SIGILL": "illegal instruction",
    "SIGINT": "interrupt",
    "SIGIO": "I/O possible",
    "SIGKILL": "killed",
    "SIGPIPE": "broken pipe",
    "SIGPROF": "profiling timer expired",
    "SIGPWR": "power failure",
    "SIGQUIT": "quit",
    "SIGSEGV": "segmentation fault",
    "SIGSTKFLT": "stack fault",
    "SIGSTOP": "stopped (signal)",
    "SIGSYS": "bad system call",
    "SIGTRAP": "trace/breakpoint trap",
    "SIGTSTP": "stopped",
    "SIGTTIN": "stopped (tty input)",
    "SIGTTOU": "stopped (tty output)",
    "SIGURG": "urgent I/O condition",
    "SIGUSR1": "user defined signal 1",
    "SIGUSR2": "user defined signal 2",
    "SIGVTALRM": "virtual timer expired",
    "SIGWINCH": "window changed",
    "SIGXCPU": "CPU time limit exceeded",
    "SIGXFSZ": "file size limit exceeded"
}

Flags

• SIGINT “Signal interrupt” – equivalent to pressing ctrl+c
• SIGQUIT “Signal quit” – requests the process quits and performs a core dump
• SIGTERM “Signal terminate” – request for a processes termination. Similar to SIGINT
• SIGUSR1 “Signal user 1” – user defined
• SIGUSR2 “Signal user 2” – user defined

Detail

The interrupts listed above are a subset of what is supported on each operating system. Please consult your operating systems docs for details on each signal and what their function is.

Windows Support

While Windows doesn’t officially support signals, the following POSIX signals are emulated:

var interrupts = map[string]syscall.Signal{
    "SIGHUP":  syscall.SIGHUP,
    "SIGINT":  syscall.SIGINT,
    "SIGQUIT": syscall.SIGQUIT,
    "SIGILL":  syscall.SIGILL,
    "SIGTRAP": syscall.SIGTRAP,
    "SIGABRT": syscall.SIGABRT,
    "SIGBUS":  syscall.SIGBUS,
    "SIGFPE":  syscall.SIGFPE,
    "SIGKILL": syscall.SIGKILL,
    "SIGSEGV": syscall.SIGSEGV,
    "SIGPIPE": syscall.SIGPIPE,
    "SIGALRM": syscall.SIGALRM,
    "SIGTERM": syscall.SIGTERM,
}

Plan 9 Support

Plan 9 is not supported.

Catching incoming signals

Signals can be caught (often referred to as “trapped”) in Murex with an event: signalTrap. Read below for details.

See Also

• Background Process (bg): Run processes in the background
• Interactive Shell: What’s different about Murex’s interactive shell?
• MUREX_EXE: Absolute path to running shell
• Murex Event Subsystem (event): Event driven programming for shell scripts
• Output String (out): Print a string to the stdout with a trailing new line character
• Terminal Hotkeys: A list of all the terminal hotkeys and their uses
• onSignalReceived: Trap OS signals

This document was generated from builtins/events/onSignalReceived/signal_doc.yaml.