- Reference manual
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().
After a signal handler is registered using this function, the native signal interface redirects the signal to a generic signal handler inside SWI-Prolog. This generic handler validates the environment, creates a suitable environment for calling the interface functions described in this chapter and finally calls the registered user-handler.
By default, signals are handled asynchronously (i.e., at the time
they arrive). It is inherently dangerous to call extensive code
fragments, and especially exception related code from asynchronous
handlers. The interface allows for synchronous handling of
signals. In this case the native OS handler just schedules the signal
which is checked by PL_handle_signals()
at the call- and redo-port. This behaviour is realised by or-ing sig
with the constant
better default would be to use synchronous handling, but this interface
preserves backward compatibility.
Signal handling routines may raise exceptions using PL_raise_exception(). The use of PL_throw() is not safe. If a synchronous handler raises an exception, the exception is delayed to the next call to PL_handle_signals();
The user may call this function inside long-running foreign functions
to handle scheduled interrupts. This routine returns the number of
signals handled. If a handler raises an exception, the return value is
-1 and the calling routine should return with
FALSE as soon
SIGor the full signal name. These refer to the same:
SIGKILL. Leaves a typed, domain or instantiation error if the conversion fails.
- int PL_compare(term_t t1, term_t t2)
- Compares two terms using the standard order of terms and returns -1, 0 or 1. See also compare/3.
- int PL_same_compound(term_t t1, term_t t2)
TRUEif t1 and t2 refer to physically the same compound term and
In some applications it is useful to store and retrieve Prolog terms from C code. For example, the XPCE graphical environment does this for storing arbitrary Prolog data as slot-data of XPCE objects.
Please note that the returned handles have no meaning at the Prolog level and the recorded terms are not visible from Prolog. The functions PL_recorded() and PL_erase() are the only functions that can operate on the stored term.
Two groups of functions are provided. The first group (PL_record() and friends) store Prolog terms on the Prolog heap for retrieval during the same session. These functions are also used by recorda/3 and friends. The recorded database may be used to communicate Prolog terms between threads.