SWI-Prolog -- API-function PL

Availability:C-language interface function

int PL_sigaction(int sig, pl_sigaction_t *act, pl_sigaction_t *oldact)

Install or query the status for signal sig. The signal is an integer between 1 and 64, where the where the signals up to 32 are mapped to OS signals and signals above that are handled by Prolog's synchronous signal handling. The pl_sigaction_t is a struct with the following definition:

typedef struct pl_sigaction
{ void        (*sa_cfunction)(int);     /* traditional C function */
  predicate_t sa_predicate;             /* call a predicate */
  int         sa_flags;                 /* additional flags */
} pl_sigaction_t;

The sa_flags is a bitwise or of PLSIG_THROW, PLSIG_SYNC and PLSIG_NOFRAME. Signal handling is enabled if PLSIG_THROW is provided, sa_cfunction or sa_predicate is provided. sa_predicate is a predicate handle for a predicate with arity 1. If no action is provided the signal handling for this signal is restored to the default before PL_initialise() was called.

Finally, 0 (zero) may be passed for sig. In that case the system allocates a free signal in the Prolog range (32 ... 64). Such signal handler are activated using PL_thread_raise().