gc_dlopen.c

/*
 * Copyright (c) 1991-1994 by Xerox Corporation.  All rights reserved.
 * Copyright (c) 1997 by Silicon Graphics.  All rights reserved.
 * Copyright (c) 2000 by Hewlett-Packard Company.  All rights reserved.
 *
 * THIS MATERIAL IS PROVIDED AS IS, WITH ABSOLUTELY NO WARRANTY EXPRESSED
 * OR IMPLIED.  ANY USE IS AT YOUR OWN RISK.
 *
 * Permission is hereby granted to use or copy this program
 * for any purpose, provided the above notices are retained on all copies.
 * Permission to modify the code and to distribute modified code is granted,
 * provided the above notices are retained, and a notice that the code was
 * modified is included with the above copyright notice.
 */

#include "private/gc_priv.h"

/* This used to be in dyn_load.c.  It was extracted into a separate     */
/* file to avoid having to link against libdl.{a,so} if the client      */
/* doesn't call dlopen.  Of course this fails if the collector is in    */
/* a dynamic library. -HB                                               */
#if defined(GC_PTHREADS) && !defined(GC_NO_DLOPEN)

#  undef GC_MUST_RESTORE_REDEFINED_DLOPEN
#  if defined(dlopen) && !defined(GC_USE_LD_WRAP)
/* To support various threads pkgs, gc.h interposes on dlopen by      */
/* defining "dlopen" to be "GC_dlopen", which is implemented below.   */
/* However, both GC_FirstDLOpenedLinkMap() and GC_dlopen() use the    */
/* real system dlopen() in their implementation. We first remove      */
/* gc.h's dlopen definition and restore it later, after GC_dlopen().  */
#    undef dlopen
#    define GC_MUST_RESTORE_REDEFINED_DLOPEN
#  endif

/* Make sure we're not in the middle of a collection, and make sure we  */
/* don't start any.  This is invoked prior to a dlopen call to avoid    */
/* synchronization issues.  We cannot just acquire the allocator lock,  */
/* since startup code in dlopen may try to allocate.  This solution     */
/* risks heap growth (or, even, heap overflow) in the presence of many  */
/* dlopen calls in either a multi-threaded environment, or if the       */
/* library initialization code allocates substantial amounts of GC'ed   */
/* memory.                                                              */
#  ifndef USE_PROC_FOR_LIBRARIES
static void
disable_gc_for_dlopen(void)
{
  LOCK();
  while (GC_incremental && GC_collection_in_progress()) {
    ENTER_GC();
    GC_collect_a_little_inner(1000);
    EXIT_GC();
  }
  ++GC_dont_gc;
  UNLOCK();
}
#  endif

/* Redefine dlopen to guarantee mutual exclusion with           */
/* GC_register_dynamic_libraries.  Should probably happen for   */
/* other operating systems, too.                                */

/* This is similar to WRAP/REAL_FUNC() in pthread_support.c.    */
#  ifdef GC_USE_LD_WRAP
#    define WRAP_DLFUNC(f) __wrap_##f
#    define REAL_DLFUNC(f) __real_##f
void *REAL_DLFUNC(dlopen)(const char *, int);
#  else
#    define WRAP_DLFUNC(f) GC_##f
#    define REAL_DLFUNC(f) f
#  endif

#  define GC_wrap_dlopen WRAP_DLFUNC(dlopen)
GC_API void *
GC_wrap_dlopen(const char *path, int mode)
{
  void *result;

#  ifndef USE_PROC_FOR_LIBRARIES
  /* Disable collections.  This solution risks heap growth (or,       */
  /* even, heap overflow) but there seems no better solutions.        */
  disable_gc_for_dlopen();
#  endif
  result = REAL_DLFUNC(dlopen)(path, mode);
#  ifndef USE_PROC_FOR_LIBRARIES
  /* This undoes disable_gc_for_dlopen().     */
  GC_enable();
#  endif
  return result;
}
#  undef GC_wrap_dlopen

#  ifdef GC_USE_LD_WRAP
/* Define GC_ function as an alias for the plain one, which will be   */
/* intercepted.  This allows files which include gc.h, and hence      */
/* generate references to the GC_ symbol, to see the right symbol.    */
GC_API void *
GC_dlopen(const char *path, int mode)
{
  return dlopen(path, mode);
}
#  endif /* GC_USE_LD_WRAP */

#  ifdef GC_MUST_RESTORE_REDEFINED_DLOPEN
#    define dlopen GC_dlopen
#  endif

#endif /* GC_PTHREADS && !GC_NO_DLOPEN */