diff --git a/src/interpret.c b/src/interpret.c
index 518524fa51d0a89f5a8e4266c08ca833c824f086..4094ff3a5bde68f7c8efe96333c7f47b51e33e8e 100644
--- a/src/interpret.c
+++ b/src/interpret.c
@@ -5,7 +5,7 @@
 \*/
 /**/
 #include "global.h"
-RCSID("$Id: interpret.c,v 1.143 2000/04/19 13:59:01 mast Exp $");
+RCSID("$Id: interpret.c,v 1.144 2000/04/19 16:03:30 mast Exp $");
 #include "interpret.h"
 #include "object.h"
 #include "program.h"
@@ -669,7 +669,7 @@ void mega_apply2(enum apply_type type, INT32 args, void *arg1, void *arg2)
     {
       THREAD_T self = th_self();
 
-      TRYLOCK_INTERPRETER_LOCK();
+      CHECK_INTERPRETER_LOCK();
 
       if( thread_id && !th_equal( OBJ2THREAD(thread_id)->id, self) )
 	fatal("Current thread is wrong.\n");
diff --git a/src/interpreter.h b/src/interpreter.h
index d590db1631733b4f1f5631632594025f485dc808..b98b728f7f39cd60ddf83b03e21a16e01b724529 100644
--- a/src/interpreter.h
+++ b/src/interpreter.h
@@ -32,10 +32,7 @@ static int eval_instruction(unsigned char *pc)
     if(d_flag)
     {
 #ifdef _REENTRANT
-#ifndef __NT__
-      if(!mt_trylock(& interpreter_lock))
-	fatal("Interpreter running unlocked!\n");
-#endif
+      CHECK_INTERPRETER_LOCK();
       if(d_flag>1 && thread_for_id(th_self()) != thread_id)
         fatal("thread_for_id() (or thread_id) failed in interpreter.h! %p != %p\n",thread_for_id(th_self()),thread_id);
 #endif
diff --git a/src/modules/HTTPLoop/accept_and_parse.c b/src/modules/HTTPLoop/accept_and_parse.c
index 04a9968088bfdcfc778ab4829a37b684fd52228b..d9f6c084d9352911c095f1b5134e0f6988609f87 100644
--- a/src/modules/HTTPLoop/accept_and_parse.c
+++ b/src/modules/HTTPLoop/accept_and_parse.c
@@ -462,7 +462,7 @@ static void low_accept_loop(struct args *arg)
 	struct cache *c, *p = NULL;
 	struct log *l, *n = NULL;
 	/* oups. */
-	mt_lock( &interpreter_lock );
+	mt_lock_interpreter();
 	for(i=0; i<CACHE_HTABLE_SIZE; i++)
 	{
 	  e = arg->cache->htable[i];
@@ -504,7 +504,7 @@ static void low_accept_loop(struct args *arg)
 	  else     aap_first_log = l->next;
 	  aap_free(l);
 	}
-	mt_unlock( &interpreter_lock );
+	mt_unlock_interpreter();
 	aap_free(arg2);
 	aap_free(arg);
 	return; /* No more accept here.. */
diff --git a/src/modules/HTTPLoop/cache.c b/src/modules/HTTPLoop/cache.c
index 5af3cc8b4efee9dea157a99aca20019357c8bbab..cfe12688d141fe3e93714e4152a1fbe74b907b2f 100644
--- a/src/modules/HTTPLoop/cache.c
+++ b/src/modules/HTTPLoop/cache.c
@@ -83,7 +83,7 @@ static int ensure_interpreter_lock( )
   {
     if( thi->swapped ) /* We are swapped out.. */
     {
-      mt_lock( &interpreter_lock );
+      mt_lock_interpreter();
       return 1;
     }
     return 0; /* we are swapped in */
@@ -93,7 +93,7 @@ static int ensure_interpreter_lock( )
   if( num_threads == 1 )
     free=num_threads++;
   wake_up_backend();
-  mt_lock( &interpreter_lock );
+  mt_lock_interpreter();
   if( free ) 
     num_threads--;
   return 1;
@@ -122,7 +122,7 @@ void aap_enqueue_string_to_free( struct pike_string *s )
     int free_interpreter_lock = ensure_interpreter_lock();
     really_free_from_queue();
     if( free_interpreter_lock )
-      mt_unlock( &interpreter_lock );
+      mt_unlock_interpreter();
   }
   free_queue[ numtofree++ ] = s;
   mt_unlock( &tofree_mutex );
diff --git a/src/modules/Java/jvm.c b/src/modules/Java/jvm.c
index d419db415b8610b9da52de142298d6a7a0f3415f..ebbe7c22dd5c9b947c27849458b55eb95eaec281 100644
--- a/src/modules/Java/jvm.c
+++ b/src/modules/Java/jvm.c
@@ -1,5 +1,5 @@
 /*
- * $Id: jvm.c,v 1.14 2000/04/04 14:11:59 marcus Exp $
+ * $Id: jvm.c,v 1.15 2000/04/19 16:03:34 mast Exp $
  *
  * Pike interface to Java Virtual Machine
  *
@@ -16,7 +16,7 @@
 #endif /* HAVE_CONFIG_H */
 
 #include "global.h"
-RCSID("$Id: jvm.c,v 1.14 2000/04/04 14:11:59 marcus Exp $");
+RCSID("$Id: jvm.c,v 1.15 2000/04/19 16:03:34 mast Exp $");
 #include "program.h"
 #include "interpret.h"
 #include "stralloc.h"
@@ -1660,18 +1660,18 @@ static void native_dispatch(struct native_method_context *ctx,
       do_native_dispatch(ctx, env, cls, args, rc);
     } else {
       /* Nope, let's get it... */
-      mt_lock(&interpreter_lock);
+      mt_lock_interpreter();
       SWAP_IN_THREAD(state);
 
       do_native_dispatch(ctx, env, cls, args, rc);
 
       /* Restore */
       SWAP_OUT_THREAD(state);
-      mt_unlock(&interpreter_lock);
+      mt_unlock_interpreter();
     }
   } else {
     /* Not a pike thread.  Create a temporary thread_id... */
-    mt_lock(&interpreter_lock);
+    mt_lock_interpreter();
     init_interpreter();
     stack_top=((char *)&state)+ (thread_stack_size-16384) * STACK_DIRECTION;
     recoveries = NULL;
@@ -1690,7 +1690,7 @@ static void native_dispatch(struct native_method_context *ctx,
     thread_id=NULL;
     cleanup_interpret();
     num_threads--;
-    mt_unlock(&interpreter_lock);
+    mt_unlock_interpreter();
   }
 }
 
diff --git a/src/modules/files/file.c b/src/modules/files/file.c
index 39d7987877a6de2c856c106f8c040c7473cc35d0..1ea621c0750bcaabbf12e21ce4a4f635109f033d 100644
--- a/src/modules/files/file.c
+++ b/src/modules/files/file.c
@@ -5,7 +5,7 @@
 \*/
 /**/
 #include "global.h"
-RCSID("$Id: file.c,v 1.173 2000/04/14 17:30:31 grubba Exp $");
+RCSID("$Id: file.c,v 1.174 2000/04/19 16:14:37 mast Exp $");
 #include "fdlib.h"
 #include "interpret.h"
 #include "svalue.h"
@@ -1362,7 +1362,7 @@ static void file_open(INT32 args)
        /* This is a temporary kluge */
        if(d_flag)
        {
-	 fprintf(stderr,"Possible gc() failiure detected in open()\n");
+	 fprintf(stderr,"Possible gc() failure detected in open()\n");
 	 describe(fp->current_object);
        }
 #endif
@@ -2389,9 +2389,9 @@ static TH_RETURN_TYPE proxy_thread(void * data)
 
   fd_close(p->to);
   fd_close(p->from);
-  mt_lock(&interpreter_lock);
+  mt_lock_interpreter();
   num_threads--;
-  mt_unlock(&interpreter_lock);
+  mt_unlock_interpreter();
   free((char *)p);
   th_exit(0);
   return 0;
@@ -2658,6 +2658,7 @@ static int PIKE_CONCAT(Y,_function_number);
 #define FILE_FUNC(X,Y,Z)					\
 void PIKE_CONCAT(Y,_ref) (INT32 args) {				\
   struct object *o=REF;						\
+  debug_malloc_touch(o);					\
   if(!o || !o->prog) { 						\
    /* This is a temporary kluge */                              \
    DO_IF_DMALLOC(						\
diff --git a/src/modules/files/sendfile.c b/src/modules/files/sendfile.c
index dc7a4f4812e472e87724e98b4c4b69468bfa2a7f..842574c812ddb99f39f453427b4de7f1b0799cb2 100644
--- a/src/modules/files/sendfile.c
+++ b/src/modules/files/sendfile.c
@@ -1,5 +1,5 @@
 /*
- * $Id: sendfile.c,v 1.37 2000/03/21 22:34:13 grubba Exp $
+ * $Id: sendfile.c,v 1.38 2000/04/19 16:03:35 mast Exp $
  *
  * Sends headers + from_fd[off..off+len-1] + trailers to to_fd asyncronously.
  *
@@ -565,7 +565,7 @@ static void worker(void *this_)
 
   low_do_sendfile(this);
 
-  mt_lock(&interpreter_lock);
+  mt_lock_interpreter();
 
   /*
    * Unlock the fd's
@@ -606,7 +606,7 @@ static void worker(void *this_)
   /* We're gone... */
   num_threads--;
     
-  mt_unlock(&interpreter_lock);
+  mt_unlock_interpreter();
 
   /* Die */
   return;
diff --git a/src/program.c b/src/program.c
index 355453cecf743c0fb511616d1d8aa96263bdc8d0..06d98682f0c70e1c16b65e024b1bbd0f367eaca4 100644
--- a/src/program.c
+++ b/src/program.c
@@ -5,7 +5,7 @@
 \*/
 /**/
 #include "global.h"
-RCSID("$Id: program.c,v 1.228 2000/04/16 16:00:35 mast Exp $");
+RCSID("$Id: program.c,v 1.229 2000/04/19 16:03:30 mast Exp $");
 #include "program.h"
 #include "object.h"
 #include "dynamic_buffer.h"
@@ -3734,11 +3734,7 @@ char *get_storage(struct object *o, struct program *p)
   int offset;
 
 #ifdef _REENTRANT
-#ifndef __NT__
-  if(d_flag)
-    if(!mt_trylock(& interpreter_lock))
-      fatal("get_storage running unlocked!\n");
-#endif
+  if(d_flag) CHECK_INTERPRETER_LOCK();
 #endif
 
   offset= low_get_storage(o->prog, p);
diff --git a/src/signal_handler.c b/src/signal_handler.c
index 9ed267d49ede498e6030d8d3587b8ec06bcb9703..be895e4649c59105245a9eaf3b8c0030a7bf6639 100644
--- a/src/signal_handler.c
+++ b/src/signal_handler.c
@@ -25,7 +25,7 @@
 #include "main.h"
 #include <signal.h>
 
-RCSID("$Id: signal_handler.c,v 1.168 2000/03/24 01:24:52 hubbe Exp $");
+RCSID("$Id: signal_handler.c,v 1.169 2000/04/19 16:03:31 mast Exp $");
 
 #ifdef HAVE_PASSWD_H
 # include <passwd.h>
@@ -1066,7 +1066,7 @@ static TH_RETURN_TYPE wait_thread(void *data)
       fprintf(stderr, "wait thread: locking interpreter, pid=%d\n",pid);
 #endif
 
-      mt_lock(&interpreter_lock);
+      mt_lock_interpreter();
 
 #ifdef PROC_DEBUG
       fprintf(stderr, "wait thread: reporting the event!\n");
@@ -1075,7 +1075,7 @@ static TH_RETURN_TYPE wait_thread(void *data)
       report_child(pid, status);
       co_broadcast(& process_status_change);
 
-      mt_unlock(&interpreter_lock);
+      mt_unlock_interpreter();
       continue;
     }
 
@@ -1134,7 +1134,7 @@ static void f_pid_status_wait(INT32 args)
   while(THIS->state == PROCESS_RUNNING)
   {
     SWAP_OUT_CURRENT_THREAD();
-    co_wait( & process_status_change, &interpreter_lock);
+    co_wait_interpreter( & process_status_change);
     SWAP_IN_CURRENT_THREAD();
   }
 
diff --git a/src/threads.c b/src/threads.c
index 5672cea4eebbd329a3e6b6ccc435981dd515f2c7..1b90be46badcd2ef582b8c4c45b364967d9bf96f 100644
--- a/src/threads.c
+++ b/src/threads.c
@@ -1,5 +1,5 @@
 #include "global.h"
-RCSID("$Id: threads.c,v 1.121 2000/04/19 13:57:36 mast Exp $");
+RCSID("$Id: threads.c,v 1.122 2000/04/19 16:03:31 mast Exp $");
 
 int num_threads = 1;
 int threads_disabled = 0;
@@ -201,6 +201,10 @@ static struct callback *threads_evaluator_callback=0;
 int thread_id_result_variable;
 
 int th_running = 0;
+#ifdef PIKE_DEBUG
+int debug_interpreter_is_locked = 0;
+THREAD_T debug_locking_thread;
+#endif
 MUTEX_T interpreter_lock, thread_table_lock, interleave_lock;
 struct program *mutex_key = 0;
 struct program *thread_id_prog = 0;
@@ -292,7 +296,7 @@ void init_threads_disable(struct object *o)
 		      (stderr,
 		       "_disable_threads(): Waiting for %d threads to finish\n",
 		       live_threads));
-      co_wait(&live_threads_change, &interpreter_lock);
+      co_wait_interpreter(&live_threads_change);
     }
     SWAP_IN_CURRENT_THREAD();
   }
@@ -559,7 +563,7 @@ TH_RETURN_TYPE new_thread_func(void * data)
   THREADS_FPRINTF(0, (stderr,"THREADS_DISALLOW() Thread %08x created...\n",
 		      (unsigned int)arg.id));
   
-  if((tmp=mt_lock( & interpreter_lock)))
+  if((tmp=mt_lock_interpreter()))
     fatal("Failed to lock interpreter, return value=%d, errno=%d\n",tmp,
 #ifdef __NT__
 	  GetLastError()
@@ -654,7 +658,7 @@ TH_RETURN_TYPE new_thread_func(void * data)
     remove_callback(threads_evaluator_callback);
     threads_evaluator_callback=0;
   }
-  mt_unlock(& interpreter_lock);
+  mt_unlock_interpreter();
   th_exit(0);
   /* NOT_REACHED, but removes a warning */
   return(NULL);
@@ -803,7 +807,7 @@ void f_mutex_lock(INT32 args)
     do
     {
       THREADS_FPRINTF(1, (stderr,"WAITING TO LOCK m:%08x\n",(unsigned int)m));
-      co_wait(& m->condition, & interpreter_lock);
+      co_wait_interpreter(& m->condition);
     }while(m->key);
     SWAP_IN_CURRENT_THREAD();
   }
@@ -969,11 +973,11 @@ void f_cond_wait(INT32 args)
     
       /* Wait and allow mutex operations */
       SWAP_OUT_CURRENT_THREAD();
-      co_wait(c, &interpreter_lock);
+      co_wait_interpreter(c);
     
       /* Lock mutex */
       while(mut->key)
-	co_wait(& mut->condition, &interpreter_lock);
+	co_wait_interpreter(& mut->condition);
       mut->key=key;
       OB2KEY(key)->mut=mut;
       
@@ -984,7 +988,7 @@ void f_cond_wait(INT32 args)
   }
 
   SWAP_OUT_CURRENT_THREAD();
-  co_wait(c, &interpreter_lock);
+  co_wait_interpreter(c);
   SWAP_IN_CURRENT_THREAD();
 
   pop_n_elems(args);
@@ -1040,7 +1044,7 @@ static void f_thread_id_result(INT32 args)
   SWAP_OUT_CURRENT_THREAD();
 
   while(th->status != THREAD_EXITED)
-    co_wait(&th->status_change, &interpreter_lock);
+    co_wait_interpreter(&th->status_change);
 
   SWAP_IN_CURRENT_THREAD();
 
@@ -1166,7 +1170,7 @@ void low_th_init(void)
 #endif /* POSIX_THREADS */
 
   mt_init( & interpreter_lock);
-  mt_lock( & interpreter_lock);
+  mt_lock_interpreter();
   mt_init( & thread_table_lock);
   mt_init( & interleave_lock);
   co_init( & live_threads_change);
diff --git a/src/threads.h b/src/threads.h
index 39550ef32a5ef58ca9060cb0e1a5966e51c2a487..ed6ad41d2fa6a40ac1c8dd13165bf72636eaacd4 100644
--- a/src/threads.h
+++ b/src/threads.h
@@ -1,5 +1,5 @@
 /*
- * $Id: threads.h,v 1.85 2000/04/19 13:57:35 mast Exp $
+ * $Id: threads.h,v 1.86 2000/04/19 16:03:31 mast Exp $
  */
 #ifndef THREADS_H
 #define THREADS_H
@@ -260,6 +260,42 @@ extern int th_running;
 
 extern PIKE_MUTEX_T interpreter_lock;
 
+#if defined(PIKE_DEBUG) && !defined(__NT__)
+
+/* This is a debug wrapper to enable checks that the interpreter lock
+ * is hold by the current thread. */
+
+extern THREAD_T debug_locking_thread;
+#define SET_LOCKING_THREAD (debug_locking_thread = th_self(), 0)
+
+#define mt_lock_interpreter() (mt_lock(&interpreter_lock) || SET_LOCKING_THREAD)
+#define mt_trylock_interpreter() (mt_trylock(&interpreter_lock) || SET_LOCKING_THREAD)
+#define mt_unlock_interpreter() (mt_unlock(&interpreter_lock))
+#define co_wait_interpreter(COND) \
+  do {co_wait((COND), &interpreter_lock); SET_LOCKING_THREAD;} while (0)
+
+#define CHECK_INTERPRETER_LOCK() do {					\
+  if (th_running) {							\
+    THREAD_T self;							\
+    if (!mt_trylock(&interpreter_lock))					\
+      fatal("Interpreter is not locked.\n");				\
+    self = th_self();							\
+    if (!th_equal(debug_locking_thread, self))				\
+      fatal("Interpreter is not locked by this thread.\n");		\
+  }									\
+} while (0)
+
+#else
+
+#define mt_lock_interpreter() (mt_lock(&interpreter_lock))
+#define mt_trylock_interpreter() (mt_trylock(&interpreter_lock))
+#define mt_unlock_interpreter() (mt_unlock(&interpreter_lock))
+#define co_wait_interpreter(COND) do {co_wait((COND), &interpreter_lock);} while (0)
+
+#define CHECK_INTERPRETER_LOCK() do {} while (0)
+
+#endif
+
 extern COND_T live_threads_change;		/* Used by _disable_threads */
 extern COND_T threads_disabled_change;		/* Used by _disable_threads */
 
@@ -478,21 +514,21 @@ struct thread_state {
        THREADS_FPRINTF(1, (stderr, "THREADS_ALLOW() %s:%d t:%08x(#%d)\n", \
 			   __FILE__, __LINE__, \
 			   (unsigned int)_tmp->thread_id, live_threads)); \
-       mt_unlock(& interpreter_lock); \
+       mt_unlock_interpreter(); \
      } else {} \
      HIDE_GLOBAL_VARIABLES()
 
 #define THREADS_DISALLOW() \
      REVEAL_GLOBAL_VARIABLES(); \
      if(_tmp->swapped) { \
-       mt_lock(& interpreter_lock); \
+       mt_lock_interpreter(); \
        THREADS_FPRINTF(1, (stderr, "THREADS_DISALLOW() %s:%d t:%08x(#%d)\n", \
 			   __FILE__, __LINE__, \
                            (unsigned int)_tmp->thread_id, live_threads)); \
        while (threads_disabled) { \
          THREADS_FPRINTF(1, (stderr, \
                              "THREADS_DISALLOW(): Threads disabled\n")); \
-         co_wait(&threads_disabled_change, &interpreter_lock); \
+         co_wait_interpreter(&threads_disabled_change); \
        } \
        SWAP_IN_THREAD(_tmp);\
      } \
@@ -514,14 +550,14 @@ struct thread_state {
        THREADS_FPRINTF(1, (stderr, "THREADS_ALLOW_UID() %s:%d t:%08x(#%d)\n", \
 			   __FILE__, __LINE__, \
 			   (unsigned int)_tmp_uid->thread_id, live_threads)); \
-       mt_unlock(& interpreter_lock); \
+       mt_unlock_interpreter(); \
      } else {} \
      HIDE_GLOBAL_VARIABLES()
 
 #define THREADS_DISALLOW_UID() \
      REVEAL_GLOBAL_VARIABLES(); \
      if(_tmp_uid->swapped) { \
-       mt_lock(& interpreter_lock); \
+       mt_lock_interpreter(); \
        live_threads--; \
        THREADS_FPRINTF(1, (stderr, \
                            "THREADS_DISALLOW_UID() %s:%d t:%08x(#%d)\n", \
@@ -530,7 +566,7 @@ struct thread_state {
        co_broadcast(&live_threads_change); \
        while (threads_disabled) { \
          THREADS_FPRINTF(1, (stderr, "THREADS_DISALLOW_UID(): Wait...\n")); \
-         co_wait(&threads_disabled_change, &interpreter_lock); \
+         co_wait_interpreter(&threads_disabled_change); \
        } \
        SWAP_IN_THREAD(_tmp_uid);\
      } \
@@ -542,36 +578,13 @@ struct thread_state {
   THREADS_DISALLOW()
 
 #ifdef PIKE_DEBUG
-
 #define ASSERT_THREAD_SWAPPED_IN() do {				\
     struct thread_state *_tmp=thread_state_for_id(th_self());	\
     if(_tmp->swapped) fatal("Thread is not swapped in!\n");	\
   }while(0)
 
-#ifdef __NT__
-#define TRYLOCK_INTERPRETER_LOCK() do {} while (0)
-#else
-#define TRYLOCK_INTERPRETER_LOCK() do {					\
-  if (th_running && !mt_trylock(&interpreter_lock))			\
-    fatal("Haven't got interpreter lock.\n");				\
-} while (0)
-#endif
-
-#define CHECK_INTERPRETER_LOCK() do {					\
-  if (th_running) {							\
-    THREAD_T self;							\
-    TRYLOCK_INTERPRETER_LOCK();						\
-    self = th_self();							\
-    if( thread_id && !th_equal( OBJ2THREAD(thread_id)->id, self) )	\
-      fatal("Current thread is wrong.\n");				\
-  }									\
-} while (0)
-
 #else
-
 #define ASSERT_THREAD_SWAPPED_IN()
-#define CHECK_INTERPRETER_LOCK() do {} while (0)
-
 #endif
 
 /* Prototypes begin here */
@@ -663,9 +676,6 @@ void th_farm(void (*fun)(void *), void *here);
 #define init_threads_disable(X)
 #define exit_threads_disable(X)
 
-#define TRYLOCK_INTERPRETER_LOCK() do {} while (0)
-#define CHECK_INTERPRETER_LOCK() do {} while (0)
-
 #endif /* PIKE_THREADS */
 
 #ifdef __NT__