## Module (chicken process signal)

This module offers procedures for dealing with POSIX process signals.

Please note that signals are very POSIX-specific. Windows only supports rudimentary in-process signals for dealing with user interrupts, segmentation violations, floating-point exceptions and the like. Inter-process signals are not supported. Therefore, most of the procedures here are not available on native Windows builds. If that's the case, the description contains a note.

### set-alarm!

set-alarm! SECONDSprocedure

  Sets an internal timer to raise the `signal/alrm` after SECONDS are elapsed. You can use the `make-signal-handler` procedure to write a handler for this signal.

  NOTE: On native Windows builds (all except cygwin), this procedure is unimplemented and will raise an error.

### make-signal-handler

make-signal-handler SIGNUM ...procedure

  Establishes a handler for the POSIX signals with the numbers `SIGNUM ...` and returns a procedure of zero or one argument. Should one of the given signals be raised, then it will be stored in a queue. Invoking the procedure returned by `make-signal-handler` with zero arguments or with the argument `#f` will remove the oldest entry in the queue and return it to the caller. Invoking the procedure with argument `#t` when no signal was raised since the creation of the signal handler or the most recent call to the handler will result in suspending the execution until one of the signals given in `SIGNUM ...` occurs.

  Notes:

  - when signals arrive in quick succession (specifically, before the handler for a signal has been started), then signals will be queued (up to a certain limit); the order in which the queued signals will be handled is not specified
  - Any signal handlers for the signals `signal/segv`, `signal/bus`, `signal/fpe` and `signal/ill` will be ignored and these signals will always trigger an exception, unless the executable was started with the `-:S` runtime option. This feature is only available on platforms that support the `sigprocmask(3)` POSIX API function.

### signal-ignore

signal-ignore SIGNUMprocedure

  Ignores any future occurrences if the signal SIGNUM by setting its disposition to `SIG_IGN`.

### signal-default

signal-default SIGNUMprocedure

  Sets the default disposition for the signal SIGNUM by setting its disposition to `SIG_DFL`.

### set-signal-mask!

set-signal-mask! SIGLISTprocedure

  Sets the signal mask of the current process to block all signals given in the list SIGLIST. Signals masked in that way will not be delivered to the current process.

  NOTE: On native Windows builds (all except cygwin), this procedure is unimplemented and will raise an error.

### signal-mask

signal-maskprocedure

  Returns the signal mask of the current process.

  NOTE: On native Windows builds (all except cygwin), this procedure is unimplemented and will raise an error.

### signal-masked?

signal-masked? SIGNUMprocedure

  Returns whether the signal for the code SIGNUM is currently masked.

  NOTE: On native Windows builds (all except cygwin), this procedure is unimplemented and will raise an error.

### signal-mask!

signal-mask! SIGNUMprocedure

  Masks (blocks) the signal for the code SIGNUM.

  NOTE: On native Windows builds (all except cygwin), this procedure is unimplemented and will raise an error.

### signal-unmask!

signal-unmask! SIGNUMprocedure

  Unmasks (unblocks) the signal for the code SIGNUM.

  NOTE: On native Windows builds (all except cygwin), this procedure is unimplemented and will raise an error.

### Signal codes

signal/termconstant
signal/killconstant
signal/intconstant
signal/hupconstant
signal/fpeconstant
signal/illconstant
signal/segvconstant
signal/abrtconstant
signal/trapconstant
signal/quitconstant
signal/alrmconstant
signal/vtalrmconstant
signal/profconstant
signal/ioconstant
signal/urgconstant
signal/chldconstant
signal/contconstant
signal/stopconstant
signal/tstpconstant
signal/pipeconstant
signal/xcpuconstant
signal/xfszconstant
signal/usr1constant
signal/usr2constant
signal/busconstant
signal/winchconstant
signal/breakconstant
signals-listconstant

  These variables contain signal codes for use with `process-signal`, `set-signal-handler!`, `signal-handler`, `signal-masked?`, `signal-mask!`, or `signal-unmask!`.

  NOTE: On native Windows builds (all except cygwin), only `signal/term`, `signal/int`, `signal/fpe`, `signal/ill`, `signal/segv`, `signal/abrt`, `signal/break` have an actual value. The others are all defined as zero, because those signals don't exist on Windows.

  NOTE: On UNIX builds and cygwin, `signal/break` is defined as zero because it only exists on Windows.

  To get a list of signals that are known to exist on the current platform, you can check `signals-list` which is a list of integers (signal numbers).

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