PATCH: wrappers, unloading, and dependencies

[Sven Wischnowsky <wischnow@informatik.hu-berlin.de>]

Hello

Another thing I forgot to mention yesterday is how dependencies are
handled when unloading modules which can't be unloaded immediately.

With the patch I send modules on which modules whose unloading is
currently delayed may be unloaded immediatly. This means that if the
wrapper function uses data or functions of the module depended upon
may fail if the access appears after the execution of the shell
function and the lower level module was unloaded (and could be
unloaded immediately).

We could make unloading of modules depended upon by modules which are 
delayed-unloaded be delayed, too. But of course that wouldn't be fully 
secure either, we would also have to enforce that modules
initialize/finalize all data other modules might be interested in in
the setup and finish functions, *not* in the boot/cleanup functions.
And that, of course, can't be guarenteed since module writers are free 
to do what they want.
Making the implementation of setup/finish mandatory might help here
but doesn't ensure the right behavior either. Side comment: without
some serious changes with modentry.c and friends we will need to make
them mandatory for AIX although I wanted to keep them optional to keep 
simple modules simple.

So we can either make find_module() be accessible from modules and add 
a comment in the documentation the this can be used in the wrapper to
test if the modules needed are still loaded or we use the patch below
to delay unloading of modules depended upon and to change the
documentation.

Which also reminds me that we still need some documentation about the
`.mdd' files...

Bye
 Sven

diff -c os/module.c Src/module.c
*** os/module.c	Wed Dec 16 10:07:35 1998
--- Src/module.c	Wed Dec 16 11:27:20 1998
***************
*** 494,520 ****
  	return m;
      } 
      m = (Module) getdata(node);
!     if (m->flags & MOD_UNLOAD) {
! 	if (init_module(m))
! 	    return NULL;
  	m->flags &= ~MOD_UNLOAD;
!     } else if (m->handle)
  	return m;
      if (m->flags & MOD_BUSY) {
  	zerr("circular dependencies for module %s", name, 0);
  	return NULL;
      }
      m->flags |= MOD_BUSY;
!     for (n = firstnode(m->deps); n; incnode(n))
! 	if (!load_module((char *) getdata(n))) {
! 	    m->flags &= ~MOD_BUSY;
! 	    return NULL;
! 	}
      m->flags &= ~MOD_BUSY;
!     if (!(m->handle = do_load_module(name)))
! 	return NULL;
      if (init_module(m)) {
! 	dlclose(m->handle);
  	m->handle = NULL;
  	return NULL;
      }
--- 494,522 ----
  	return m;
      } 
      m = (Module) getdata(node);
!     if (m->flags & MOD_UNLOAD)
  	m->flags &= ~MOD_UNLOAD;
!     else if (m->handle)
  	return m;
      if (m->flags & MOD_BUSY) {
  	zerr("circular dependencies for module %s", name, 0);
  	return NULL;
      }
      m->flags |= MOD_BUSY;
!     if (m->deps)
! 	for (n = firstnode(m->deps); n; incnode(n))
! 	    if (!load_module((char *) getdata(n))) {
! 		m->flags &= ~MOD_BUSY;
! 		return NULL;
! 	    }
      m->flags &= ~MOD_BUSY;
!     if (!m->handle) {
! 	if (!(m->handle = do_load_module(name)))
! 	    return NULL;
! 	setup_module(m);
!     }
      if (init_module(m)) {
! 	finish_module(m->handle);
  	m->handle = NULL;
  	return NULL;
      }
***************
*** 796,801 ****
--- 798,805 ----
      if (m->handle && !(m->flags & MOD_UNLOAD) && cleanup_module(m))
  	return 1;
      else {
+ 	int del = (m->flags & MOD_UNLOAD);
+ 
  	if (m->wrapper) {
  	    m->flags |= MOD_UNLOAD;
  	    return 0;
***************
*** 804,809 ****
--- 808,847 ----
  	if (m->handle)
  	    finish_module(m);
  	m->handle = NULL;
+ 	if (del && m->deps) {
+ 	    /* The module was unloaded delayed, unload all modules *
+ 	     * on which it depended. */
+ 	    LinkNode n;
+ 
+ 	    for (n = firstnode(m->deps); n; incnode(n)) {
+ 		LinkNode dn = find_module((char *) getdata(n));
+ 		Module dm;
+ 
+ 		if (dn && (dm = (Module) getdata(dn)) &&
+ 		    (dm->flags & MOD_UNLOAD)) {
+ 		    /* See if this is the only module depending on it. */
+ 
+ 		    LinkNode an;
+ 		    Module am;
+ 		    int du = 1;
+ 
+ 		    for (an = firstnode(modules); du && an; incnode(an)) {
+ 			am = (Module) getdata(an);
+ 			if (am != m && am->handle && am->deps) {
+ 			    LinkNode sn;
+ 
+ 			    for (sn = firstnode(am->deps); du && sn;
+ 				 incnode(sn)) {
+ 				if (!strcmp((char *) getdata(sn), dm->nam))
+ 				    du = 0;
+ 			    }
+ 			}
+ 		    }
+ 		    if (du)
+ 			unload_module(dm, NULL);
+ 		}
+ 	    }
+ 	}
  	if(!m->deps) {
  	    if (!node) {
  		for (node = firstnode(modules); node; incnode(node))
***************
*** 833,852 ****
  	    node = find_module(*args);
  	    if (node) {
  		LinkNode mn, dn;
  
  		for (mn = firstnode(modules); mn; incnode(mn)) {
  		    m = (Module) getdata(mn);
! 		    if (!(m->flags & MOD_UNLOAD) && m->deps && m->handle)
  			for (dn = firstnode(m->deps); dn; incnode(dn))
  			    if (!strcmp((char *) getdata(dn), *args)) {
! 				zwarnnam(nam, "module %s is in use by another module and cannot be unloaded", *args, 0);
! 				ret = 1;
! 				goto cont;
  			    }
  		}
  		m = (Module) getdata(node);
  		if (unload_module(m, node))
  		    ret = 1;
  	    } else if (!ops['i']) {
  		zwarnnam(nam, "no such module %s", *args, 0);
  		ret = 1;
--- 871,899 ----
  	    node = find_module(*args);
  	    if (node) {
  		LinkNode mn, dn;
+ 		int del = 0;
  
  		for (mn = firstnode(modules); mn; incnode(mn)) {
  		    m = (Module) getdata(mn);
! 		    if (m->deps && m->handle)
  			for (dn = firstnode(m->deps); dn; incnode(dn))
  			    if (!strcmp((char *) getdata(dn), *args)) {
! 				if (m->flags & MOD_UNLOAD)
! 				    del = 1;
! 				else {
! 				    zwarnnam(nam, "module %s is in use by another module and cannot be unloaded", *args, 0);
! 				    ret = 1;
! 				    goto cont;
! 				}
  			    }
  		}
  		m = (Module) getdata(node);
+ 		if (del)
+ 		    m->wrapper++;
  		if (unload_module(m, node))
  		    ret = 1;
+ 		if (del)
+ 		    m->wrapper--;
  	    } else if (!ops['i']) {
  		zwarnnam(nam, "no such module %s", *args, 0);
  		ret = 1;
*** Util/zsh-development-guide.old	Wed Dec 16 10:22:11 1998
--- Util/zsh-development-guide	Wed Dec 16 11:38:39 1998
***************
*** 362,367 ****
--- 362,372 ----
  guaranteed that the data needed by the wrapper function is still valid 
  when wrappers are active and that the user-visible interface defined
  by the module disappears as soon as the user tries to unload a module.
+ Modules other modules which are currently delayed unloaded depend upon 
+ are unloaded delayed, too. This means that whenever you write a module 
+ that exports some data or functions which might be interesting to
+ other modules you make sure that they are initialized and finalized in 
+ the setup- und finish-functions, not in the boot- and cleanup-functions.
  
  Documentation
  -------------

--
Sven Wischnowsky                         wischnow@informatik.hu-berlin.de