Initializing Guile
==================

Each thread that wants to use functions from the Guile API needs to put itself into guile mode with either scm_with_guile or 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 scm_without_guile, see Blocking.

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

 -- C Function: void * scm_with_guile (void *(*func)(void *), void *data)
     Call FUNC, passing it DATA and return what FUNC returns.  While FUNC is running, the current thread is in guile mode and can thus use the Guile API.

     When scm_with_guile is called from guile mode, the thread remains in guile mode when 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 all-threads, for example.  This Scheme representation is not removed when 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 func.

     The function FUNC is called via scm_with_continuation_barrier; thus, scm_with_guile returns exactly once.

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

     It is OK to call scm_with_guile while a thread has temporarily left guile mode via scm_without_guile.  It will then simply temporarily enter guile mode again.

 -- 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 scm_with_guile.  That is, all functions called by the current thread can assume that SCM values on their stack frames are protected from the garbage collector (except when the thread has explicitly left guile mode, of course).

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

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

     The function 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 scm_with_guile or its variation scm_boot_guile instead of this function.

 -- C Function: void scm_boot_guile (int ARGC, char **ARGV, void (*MAIN_FUNC) (void *DATA, int ARGC, char **ARGV), void *DATA)
     Enter guile mode as with scm_with_guile and call MAIN_FUNC, passing it DATA, ARGC, and ARGV as indicated.  When MAIN_FUNC returns, scm_boot_guile calls exit (0); scm_boot_guile never returns.  If you want some other exit value, have MAIN_FUNC call exit itself.  If you don't want to exit at all, use scm_with_guile instead of scm_boot_guile.

     The function scm_boot_guile arranges for the Scheme command-line function to return the strings given by ARGC and ARGV.  If MAIN_FUNC modifies ARGC or ARGV, it should call scm_set_program_arguments with the final list, so Scheme code will know which arguments have been processed (see Runtime Environment).

 -- C Function: void scm_shell (int ARGC, char **ARGV)
     Process command-line arguments in the manner of the guile executable.  This includes loading the normal Guile initialization files, interacting with the user or running any scripts or expressions specified by -s or -e options, and then exiting. See Invoking Guile, for more details.

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