guile/doc/ref/api-init.texi

@c -*-texinfo-*-
@c This is part of the GNU Guile Reference Manual.
@c Copyright (C)  1996, 1997, 2000, 2001, 2002, 2003, 2004, 2007
@c   Free Software Foundation, Inc.
@c See the file guile.texi for copying conditions.


@node Initialization
@section Initializing Guile
@cindex Initializing Guile

Each thread that wants to use functions from the Guile API needs to
put itself into guile mode with either @code{scm_with_guile} or
@code{scm_init_guile}.  The global state of Guile is initialized
automatically when the first thread enters guile mode.

When a thread wants to block outside of a Guile API function, it
should leave guile mode temporarily with @code{scm_without_guile},
@xref{Blocking}.

Threads that are created by @code{call-with-new-thread} or
@code{scm_spawn_thread} start out in guile mode so you don't need to
initialize them.

@deftypefn {C Function} {void *} scm_with_guile (void *(*func)(void *), void *data)
Call @var{func}, passing it @var{data} and return what @var{func}
returns.  While @var{func} is running, the current thread is in guile
mode and can thus use the Guile API.

When @code{scm_with_guile} is called from guile mode, the thread remains
in guile mode when @code{scm_with_guile} returns.

Otherwise, it puts the current thread into guile mode and, if needed,
gives it a Scheme representation that is contained in the list returned
by @code{all-threads}, for example.  This Scheme representation is not
removed when @code{scm_with_guile} returns so that a given thread is
always represented by the same Scheme value during its lifetime, if at
all.

When this is the first thread that enters guile mode, the global state
of Guile is initialized before calling @code{func}.

The function @var{func} is called via
@code{scm_with_continuation_barrier}; thus, @code{scm_with_guile}
returns exactly once.

When @code{scm_with_guile} returns, the thread is no longer in guile
mode (except when @code{scm_with_guile} was called from guile mode, see
above).  Thus, only @code{func} can store @code{SCM} variables on the
stack and be sure that they are protected from the garbage collector.
See @code{scm_init_guile} for another approach at initializing Guile
that does not have this restriction.

It is OK to call @code{scm_with_guile} while a thread has temporarily
left guile mode via @code{scm_without_guile}.  It will then simply
temporarily enter guile mode again.
@end deftypefn

@deftypefn {C Function} void scm_init_guile ()
Arrange things so that all of the code in the current thread executes as
if from within a call to @code{scm_with_guile}.  That is, all functions
called by the current thread can assume that @code{SCM} values on their
stack frames are protected from the garbage collector (except when the
thread has explicitely left guile mode, of course).

When @code{scm_init_guile} is called from a thread that already has been
in guile mode once, nothing happens.  This behavior matters when you
call @code{scm_init_guile} while the thread has only temporarily left
guile mode: in that case the thread will not be in guile mode after
@code{scm_init_guile} returns.  Thus, you should not use
@code{scm_init_guile} in such a scenario.

When a uncaught throw happens in a thread that has been put into guile
mode via @code{scm_init_guile}, a short message is printed to the
current error port and the thread is exited via @code{scm_pthread_exit
(NULL)}.  No restrictions are placed on continuations.

The function @code{scm_init_guile} might not be available on all
platforms since it requires some stack-bounds-finding magic that might
not have been ported to all platforms that Guile runs on.  Thus, if you
can, it is better to use @code{scm_with_guile} or its variation
@code{scm_boot_guile} instead of this function.
@end deftypefn

@deftypefn {C Function} void scm_boot_guile (int @var{argc}, char **@var{argv}, void (*@var{main_func}) (void *@var{data}, int @var{argc}, char **@var{argv}), void *@var{data})
Enter guile mode as with @code{scm_with_guile} and call @var{main_func},
passing it @var{data}, @var{argc}, and @var{argv} as indicated.  When
@var{main_func} returns, @code{scm_boot_guile} calls @code{exit (0)};
@code{scm_boot_guile} never returns.  If you want some other exit value,
have @var{main_func} call @code{exit} itself.  If you don't want to exit
at all, use @code{scm_with_guile} instead of @code{scm_boot_guile}.

The function @code{scm_boot_guile} arranges for the Scheme
@code{command-line} function to return the strings given by @var{argc}
and @var{argv}.  If @var{main_func} modifies @var{argc} or @var{argv},
it should call @code{scm_set_program_arguments} with the final list, so
Scheme code will know which arguments have been processed
(@pxref{Runtime Environment}).
@end deftypefn

@deftypefn {C Function} void scm_shell (int @var{argc}, char **@var{argv})
Process command-line arguments in the manner of the @code{guile}
executable.  This includes loading the normal Guile initialization
files, interacting with the user or running any scripts or expressions
specified by @code{-s} or @code{-e} options, and then exiting.
@xref{Invoking Guile}, for more details.

Since this function does not return, you must do all
application-specific initialization before calling this function.
@end deftypefn